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7ddedebb TI |
1 | ====================== |
2 | Writing an ALSA Driver | |
3 | ====================== | |
4 | ||
5 | :Author: Takashi Iwai <tiwai@suse.de> | |
7ddedebb TI |
6 | |
7 | Preface | |
8 | ======= | |
9 | ||
10 | This document describes how to write an `ALSA (Advanced Linux Sound | |
11 | Architecture) <http://www.alsa-project.org/>`__ driver. The document | |
12 | focuses mainly on PCI soundcards. In the case of other device types, the | |
13 | API might be different, too. However, at least the ALSA kernel API is | |
14 | consistent, and therefore it would be still a bit help for writing them. | |
15 | ||
16 | This document targets people who already have enough C language skills | |
17 | and have basic linux kernel programming knowledge. This document doesn't | |
18 | explain the general topic of linux kernel coding and doesn't cover | |
19 | low-level driver implementation details. It only describes the standard | |
20 | way to write a PCI sound driver on ALSA. | |
21 | ||
7ddedebb TI |
22 | This document is still a draft version. Any feedback and corrections, |
23 | please!! | |
24 | ||
25 | File Tree Structure | |
26 | =================== | |
27 | ||
28 | General | |
29 | ------- | |
30 | ||
f90afe79 | 31 | The file tree structure of ALSA driver is depicted below. |
7ddedebb TI |
32 | |
33 | :: | |
34 | ||
35 | sound | |
36 | /core | |
37 | /oss | |
38 | /seq | |
39 | /oss | |
7ddedebb TI |
40 | /include |
41 | /drivers | |
42 | /mpu401 | |
43 | /opl3 | |
44 | /i2c | |
7ddedebb TI |
45 | /synth |
46 | /emux | |
47 | /pci | |
48 | /(cards) | |
49 | /isa | |
50 | /(cards) | |
51 | /arm | |
52 | /ppc | |
53 | /sparc | |
54 | /usb | |
55 | /pcmcia /(cards) | |
f90afe79 | 56 | /soc |
7ddedebb TI |
57 | /oss |
58 | ||
59 | ||
60 | core directory | |
61 | -------------- | |
62 | ||
63 | This directory contains the middle layer which is the heart of ALSA | |
64 | drivers. In this directory, the native ALSA modules are stored. The | |
65 | sub-directories contain different modules and are dependent upon the | |
66 | kernel config. | |
67 | ||
68 | core/oss | |
69 | ~~~~~~~~ | |
70 | ||
71 | The codes for PCM and mixer OSS emulation modules are stored in this | |
72 | directory. The rawmidi OSS emulation is included in the ALSA rawmidi | |
73 | code since it's quite small. The sequencer code is stored in | |
74 | ``core/seq/oss`` directory (see `below <#core-seq-oss>`__). | |
75 | ||
7ddedebb TI |
76 | core/seq |
77 | ~~~~~~~~ | |
78 | ||
79 | This directory and its sub-directories are for the ALSA sequencer. This | |
80 | directory contains the sequencer core and primary sequencer modules such | |
81 | like snd-seq-midi, snd-seq-virmidi, etc. They are compiled only when | |
82 | ``CONFIG_SND_SEQUENCER`` is set in the kernel config. | |
83 | ||
84 | core/seq/oss | |
85 | ~~~~~~~~~~~~ | |
86 | ||
87 | This contains the OSS sequencer emulation codes. | |
88 | ||
7ddedebb TI |
89 | include directory |
90 | ----------------- | |
91 | ||
92 | This is the place for the public header files of ALSA drivers, which are | |
93 | to be exported to user-space, or included by several files at different | |
94 | directories. Basically, the private header files should not be placed in | |
95 | this directory, but you may still find files there, due to historical | |
96 | reasons :) | |
97 | ||
98 | drivers directory | |
99 | ----------------- | |
100 | ||
101 | This directory contains code shared among different drivers on different | |
102 | architectures. They are hence supposed not to be architecture-specific. | |
103 | For example, the dummy pcm driver and the serial MIDI driver are found | |
104 | in this directory. In the sub-directories, there is code for components | |
105 | which are independent from bus and cpu architectures. | |
106 | ||
107 | drivers/mpu401 | |
108 | ~~~~~~~~~~~~~~ | |
109 | ||
110 | The MPU401 and MPU401-UART modules are stored here. | |
111 | ||
112 | drivers/opl3 and opl4 | |
113 | ~~~~~~~~~~~~~~~~~~~~~ | |
114 | ||
115 | The OPL3 and OPL4 FM-synth stuff is found here. | |
116 | ||
117 | i2c directory | |
118 | ------------- | |
119 | ||
120 | This contains the ALSA i2c components. | |
121 | ||
122 | Although there is a standard i2c layer on Linux, ALSA has its own i2c | |
123 | code for some cards, because the soundcard needs only a simple operation | |
124 | and the standard i2c API is too complicated for such a purpose. | |
125 | ||
7ddedebb TI |
126 | synth directory |
127 | --------------- | |
128 | ||
129 | This contains the synth middle-level modules. | |
130 | ||
131 | So far, there is only Emu8000/Emu10k1 synth driver under the | |
132 | ``synth/emux`` sub-directory. | |
133 | ||
134 | pci directory | |
135 | ------------- | |
136 | ||
137 | This directory and its sub-directories hold the top-level card modules | |
138 | for PCI soundcards and the code specific to the PCI BUS. | |
139 | ||
140 | The drivers compiled from a single file are stored directly in the pci | |
141 | directory, while the drivers with several source files are stored on | |
142 | their own sub-directory (e.g. emu10k1, ice1712). | |
143 | ||
144 | isa directory | |
145 | ------------- | |
146 | ||
147 | This directory and its sub-directories hold the top-level card modules | |
148 | for ISA soundcards. | |
149 | ||
150 | arm, ppc, and sparc directories | |
151 | ------------------------------- | |
152 | ||
153 | They are used for top-level card modules which are specific to one of | |
154 | these architectures. | |
155 | ||
156 | usb directory | |
157 | ------------- | |
158 | ||
159 | This directory contains the USB-audio driver. In the latest version, the | |
160 | USB MIDI driver is integrated in the usb-audio driver. | |
161 | ||
162 | pcmcia directory | |
163 | ---------------- | |
164 | ||
165 | The PCMCIA, especially PCCard drivers will go here. CardBus drivers will | |
166 | be in the pci directory, because their API is identical to that of | |
167 | standard PCI cards. | |
168 | ||
f90afe79 TI |
169 | soc directory |
170 | ------------- | |
171 | ||
172 | This directory contains the codes for ASoC (ALSA System on Chip) | |
173 | layer including ASoC core, codec and machine drivers. | |
174 | ||
7ddedebb TI |
175 | oss directory |
176 | ------------- | |
177 | ||
f90afe79 TI |
178 | Here contains OSS/Lite codes. |
179 | All codes have been deprecated except for dmasound on m68k as of | |
180 | writing this. | |
181 | ||
7ddedebb TI |
182 | |
183 | Basic Flow for PCI Drivers | |
184 | ========================== | |
185 | ||
186 | Outline | |
187 | ------- | |
188 | ||
189 | The minimum flow for PCI soundcards is as follows: | |
190 | ||
191 | - define the PCI ID table (see the section `PCI Entries`_). | |
192 | ||
193 | - create ``probe`` callback. | |
194 | ||
195 | - create ``remove`` callback. | |
196 | ||
197 | - create a :c:type:`struct pci_driver <pci_driver>` structure | |
198 | containing the three pointers above. | |
199 | ||
200 | - create an ``init`` function just calling the | |
201 | :c:func:`pci_register_driver()` to register the pci_driver | |
202 | table defined above. | |
203 | ||
204 | - create an ``exit`` function to call the | |
205 | :c:func:`pci_unregister_driver()` function. | |
206 | ||
207 | Full Code Example | |
208 | ----------------- | |
209 | ||
210 | The code example is shown below. Some parts are kept unimplemented at | |
211 | this moment but will be filled in the next sections. The numbers in the | |
212 | comment lines of the :c:func:`snd_mychip_probe()` function refer | |
213 | to details explained in the following section. | |
214 | ||
215 | :: | |
216 | ||
217 | #include <linux/init.h> | |
218 | #include <linux/pci.h> | |
219 | #include <linux/slab.h> | |
220 | #include <sound/core.h> | |
221 | #include <sound/initval.h> | |
222 | ||
223 | /* module parameters (see "Module Parameters") */ | |
224 | /* SNDRV_CARDS: maximum number of cards supported by this module */ | |
225 | static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX; | |
226 | static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR; | |
227 | static bool enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP; | |
228 | ||
229 | /* definition of the chip-specific record */ | |
230 | struct mychip { | |
231 | struct snd_card *card; | |
232 | /* the rest of the implementation will be in section | |
233 | * "PCI Resource Management" | |
234 | */ | |
235 | }; | |
236 | ||
237 | /* chip-specific destructor | |
238 | * (see "PCI Resource Management") | |
239 | */ | |
240 | static int snd_mychip_free(struct mychip *chip) | |
241 | { | |
242 | .... /* will be implemented later... */ | |
243 | } | |
244 | ||
245 | /* component-destructor | |
246 | * (see "Management of Cards and Components") | |
247 | */ | |
248 | static int snd_mychip_dev_free(struct snd_device *device) | |
249 | { | |
250 | return snd_mychip_free(device->device_data); | |
251 | } | |
252 | ||
253 | /* chip-specific constructor | |
254 | * (see "Management of Cards and Components") | |
255 | */ | |
256 | static int snd_mychip_create(struct snd_card *card, | |
257 | struct pci_dev *pci, | |
258 | struct mychip **rchip) | |
259 | { | |
260 | struct mychip *chip; | |
261 | int err; | |
262 | static struct snd_device_ops ops = { | |
263 | .dev_free = snd_mychip_dev_free, | |
264 | }; | |
265 | ||
266 | *rchip = NULL; | |
267 | ||
268 | /* check PCI availability here | |
269 | * (see "PCI Resource Management") | |
270 | */ | |
271 | .... | |
272 | ||
273 | /* allocate a chip-specific data with zero filled */ | |
274 | chip = kzalloc(sizeof(*chip), GFP_KERNEL); | |
275 | if (chip == NULL) | |
276 | return -ENOMEM; | |
277 | ||
278 | chip->card = card; | |
279 | ||
280 | /* rest of initialization here; will be implemented | |
281 | * later, see "PCI Resource Management" | |
282 | */ | |
283 | .... | |
284 | ||
285 | err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops); | |
286 | if (err < 0) { | |
287 | snd_mychip_free(chip); | |
288 | return err; | |
289 | } | |
290 | ||
291 | *rchip = chip; | |
292 | return 0; | |
293 | } | |
294 | ||
295 | /* constructor -- see "Driver Constructor" sub-section */ | |
296 | static int snd_mychip_probe(struct pci_dev *pci, | |
297 | const struct pci_device_id *pci_id) | |
298 | { | |
299 | static int dev; | |
300 | struct snd_card *card; | |
301 | struct mychip *chip; | |
302 | int err; | |
303 | ||
304 | /* (1) */ | |
305 | if (dev >= SNDRV_CARDS) | |
306 | return -ENODEV; | |
307 | if (!enable[dev]) { | |
308 | dev++; | |
309 | return -ENOENT; | |
310 | } | |
311 | ||
312 | /* (2) */ | |
313 | err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE, | |
314 | 0, &card); | |
315 | if (err < 0) | |
316 | return err; | |
317 | ||
318 | /* (3) */ | |
319 | err = snd_mychip_create(card, pci, &chip); | |
f90afe79 TI |
320 | if (err < 0) |
321 | goto error; | |
7ddedebb TI |
322 | |
323 | /* (4) */ | |
324 | strcpy(card->driver, "My Chip"); | |
325 | strcpy(card->shortname, "My Own Chip 123"); | |
326 | sprintf(card->longname, "%s at 0x%lx irq %i", | |
4b81dad1 | 327 | card->shortname, chip->port, chip->irq); |
7ddedebb TI |
328 | |
329 | /* (5) */ | |
330 | .... /* implemented later */ | |
331 | ||
332 | /* (6) */ | |
333 | err = snd_card_register(card); | |
f90afe79 TI |
334 | if (err < 0) |
335 | goto error; | |
7ddedebb TI |
336 | |
337 | /* (7) */ | |
338 | pci_set_drvdata(pci, card); | |
339 | dev++; | |
340 | return 0; | |
f90afe79 TI |
341 | |
342 | error: | |
343 | snd_card_free(card); | |
344 | return err; | |
7ddedebb TI |
345 | } |
346 | ||
347 | /* destructor -- see the "Destructor" sub-section */ | |
348 | static void snd_mychip_remove(struct pci_dev *pci) | |
349 | { | |
350 | snd_card_free(pci_get_drvdata(pci)); | |
7ddedebb TI |
351 | } |
352 | ||
353 | ||
354 | ||
355 | Driver Constructor | |
356 | ------------------ | |
357 | ||
358 | The real constructor of PCI drivers is the ``probe`` callback. The | |
359 | ``probe`` callback and other component-constructors which are called | |
360 | from the ``probe`` callback cannot be used with the ``__init`` prefix | |
361 | because any PCI device could be a hotplug device. | |
362 | ||
363 | In the ``probe`` callback, the following scheme is often used. | |
364 | ||
365 | 1) Check and increment the device index. | |
366 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
367 | ||
368 | :: | |
369 | ||
370 | static int dev; | |
371 | .... | |
372 | if (dev >= SNDRV_CARDS) | |
373 | return -ENODEV; | |
374 | if (!enable[dev]) { | |
375 | dev++; | |
376 | return -ENOENT; | |
377 | } | |
378 | ||
379 | ||
380 | where ``enable[dev]`` is the module option. | |
381 | ||
382 | Each time the ``probe`` callback is called, check the availability of | |
383 | the device. If not available, simply increment the device index and | |
384 | returns. dev will be incremented also later (`step 7 | |
385 | <#set-the-pci-driver-data-and-return-zero>`__). | |
386 | ||
387 | 2) Create a card instance | |
388 | ~~~~~~~~~~~~~~~~~~~~~~~~~ | |
389 | ||
390 | :: | |
391 | ||
392 | struct snd_card *card; | |
393 | int err; | |
394 | .... | |
395 | err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE, | |
396 | 0, &card); | |
397 | ||
398 | ||
399 | The details will be explained in the section `Management of Cards and | |
400 | Components`_. | |
401 | ||
402 | 3) Create a main component | |
403 | ~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
404 | ||
405 | In this part, the PCI resources are allocated. | |
406 | ||
407 | :: | |
408 | ||
409 | struct mychip *chip; | |
410 | .... | |
411 | err = snd_mychip_create(card, pci, &chip); | |
f90afe79 TI |
412 | if (err < 0) |
413 | goto error; | |
7ddedebb TI |
414 | |
415 | The details will be explained in the section `PCI Resource | |
416 | Management`_. | |
417 | ||
f90afe79 TI |
418 | When something goes wrong, the probe function needs to deal with the |
419 | error. In this example, we have a single error handling path placed | |
420 | at the end of the function. | |
421 | ||
422 | :: | |
423 | ||
424 | error: | |
425 | snd_card_free(card); | |
426 | return err; | |
427 | ||
428 | Since each component can be properly freed, the single | |
429 | :c:func:`snd_card_free()` call should suffice in most cases. | |
430 | ||
431 | ||
7ddedebb TI |
432 | 4) Set the driver ID and name strings. |
433 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
434 | ||
435 | :: | |
436 | ||
437 | strcpy(card->driver, "My Chip"); | |
438 | strcpy(card->shortname, "My Own Chip 123"); | |
439 | sprintf(card->longname, "%s at 0x%lx irq %i", | |
4b81dad1 | 440 | card->shortname, chip->port, chip->irq); |
7ddedebb TI |
441 | |
442 | The driver field holds the minimal ID string of the chip. This is used | |
443 | by alsa-lib's configurator, so keep it simple but unique. Even the | |
444 | same driver can have different driver IDs to distinguish the | |
445 | functionality of each chip type. | |
446 | ||
447 | The shortname field is a string shown as more verbose name. The longname | |
448 | field contains the information shown in ``/proc/asound/cards``. | |
449 | ||
450 | 5) Create other components, such as mixer, MIDI, etc. | |
451 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
452 | ||
453 | Here you define the basic components such as `PCM <#PCM-Interface>`__, | |
454 | mixer (e.g. `AC97 <#API-for-AC97-Codec>`__), MIDI (e.g. | |
455 | `MPU-401 <#MIDI-MPU401-UART-Interface>`__), and other interfaces. | |
456 | Also, if you want a `proc file <#Proc-Interface>`__, define it here, | |
457 | too. | |
458 | ||
459 | 6) Register the card instance. | |
460 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
461 | ||
462 | :: | |
463 | ||
464 | err = snd_card_register(card); | |
f90afe79 TI |
465 | if (err < 0) |
466 | goto error; | |
7ddedebb TI |
467 | |
468 | Will be explained in the section `Management of Cards and | |
469 | Components`_, too. | |
470 | ||
471 | 7) Set the PCI driver data and return zero. | |
472 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
473 | ||
474 | :: | |
475 | ||
476 | pci_set_drvdata(pci, card); | |
477 | dev++; | |
478 | return 0; | |
479 | ||
480 | In the above, the card record is stored. This pointer is used in the | |
481 | remove callback and power-management callbacks, too. | |
482 | ||
483 | Destructor | |
484 | ---------- | |
485 | ||
486 | The destructor, remove callback, simply releases the card instance. Then | |
487 | the ALSA middle layer will release all the attached components | |
488 | automatically. | |
489 | ||
f90afe79 | 490 | It would be typically just :c:func:`calling snd_card_free()`: |
7ddedebb TI |
491 | |
492 | :: | |
493 | ||
494 | static void snd_mychip_remove(struct pci_dev *pci) | |
495 | { | |
496 | snd_card_free(pci_get_drvdata(pci)); | |
7ddedebb TI |
497 | } |
498 | ||
499 | ||
500 | The above code assumes that the card pointer is set to the PCI driver | |
501 | data. | |
502 | ||
503 | Header Files | |
504 | ------------ | |
505 | ||
506 | For the above example, at least the following include files are | |
507 | necessary. | |
508 | ||
509 | :: | |
510 | ||
511 | #include <linux/init.h> | |
512 | #include <linux/pci.h> | |
513 | #include <linux/slab.h> | |
514 | #include <sound/core.h> | |
515 | #include <sound/initval.h> | |
516 | ||
517 | where the last one is necessary only when module options are defined | |
518 | in the source file. If the code is split into several files, the files | |
519 | without module options don't need them. | |
520 | ||
521 | In addition to these headers, you'll need ``<linux/interrupt.h>`` for | |
f90afe79 | 522 | interrupt handling, and ``<linux/io.h>`` for I/O access. If you use the |
7ddedebb TI |
523 | :c:func:`mdelay()` or :c:func:`udelay()` functions, you'll need |
524 | to include ``<linux/delay.h>`` too. | |
525 | ||
526 | The ALSA interfaces like the PCM and control APIs are defined in other | |
527 | ``<sound/xxx.h>`` header files. They have to be included after | |
528 | ``<sound/core.h>``. | |
529 | ||
530 | Management of Cards and Components | |
531 | ================================== | |
532 | ||
533 | Card Instance | |
534 | ------------- | |
535 | ||
536 | For each soundcard, a “card” record must be allocated. | |
537 | ||
538 | A card record is the headquarters of the soundcard. It manages the whole | |
539 | list of devices (components) on the soundcard, such as PCM, mixers, | |
540 | MIDI, synthesizer, and so on. Also, the card record holds the ID and the | |
541 | name strings of the card, manages the root of proc files, and controls | |
542 | the power-management states and hotplug disconnections. The component | |
543 | list on the card record is used to manage the correct release of | |
544 | resources at destruction. | |
545 | ||
546 | As mentioned above, to create a card instance, call | |
547 | :c:func:`snd_card_new()`. | |
548 | ||
549 | :: | |
550 | ||
551 | struct snd_card *card; | |
552 | int err; | |
553 | err = snd_card_new(&pci->dev, index, id, module, extra_size, &card); | |
554 | ||
555 | ||
556 | The function takes six arguments: the parent device pointer, the | |
557 | card-index number, the id string, the module pointer (usually | |
558 | ``THIS_MODULE``), the size of extra-data space, and the pointer to | |
559 | return the card instance. The extra_size argument is used to allocate | |
560 | card->private_data for the chip-specific data. Note that these data are | |
561 | allocated by :c:func:`snd_card_new()`. | |
562 | ||
563 | The first argument, the pointer of struct :c:type:`struct device | |
564 | <device>`, specifies the parent device. For PCI devices, typically | |
565 | ``&pci->`` is passed there. | |
566 | ||
567 | Components | |
568 | ---------- | |
569 | ||
570 | After the card is created, you can attach the components (devices) to | |
571 | the card instance. In an ALSA driver, a component is represented as a | |
572 | :c:type:`struct snd_device <snd_device>` object. A component | |
573 | can be a PCM instance, a control interface, a raw MIDI interface, etc. | |
574 | Each such instance has one component entry. | |
575 | ||
576 | A component can be created via :c:func:`snd_device_new()` | |
577 | function. | |
578 | ||
579 | :: | |
580 | ||
581 | snd_device_new(card, SNDRV_DEV_XXX, chip, &ops); | |
582 | ||
583 | This takes the card pointer, the device-level (``SNDRV_DEV_XXX``), the | |
584 | data pointer, and the callback pointers (``&ops``). The device-level | |
585 | defines the type of components and the order of registration and | |
586 | de-registration. For most components, the device-level is already | |
587 | defined. For a user-defined component, you can use | |
588 | ``SNDRV_DEV_LOWLEVEL``. | |
589 | ||
590 | This function itself doesn't allocate the data space. The data must be | |
591 | allocated manually beforehand, and its pointer is passed as the | |
592 | argument. This pointer (``chip`` in the above example) is used as the | |
593 | identifier for the instance. | |
594 | ||
595 | Each pre-defined ALSA component such as ac97 and pcm calls | |
596 | :c:func:`snd_device_new()` inside its constructor. The destructor | |
597 | for each component is defined in the callback pointers. Hence, you don't | |
598 | need to take care of calling a destructor for such a component. | |
599 | ||
600 | If you wish to create your own component, you need to set the destructor | |
601 | function to the dev_free callback in the ``ops``, so that it can be | |
602 | released automatically via :c:func:`snd_card_free()`. The next | |
603 | example will show an implementation of chip-specific data. | |
604 | ||
605 | Chip-Specific Data | |
606 | ------------------ | |
607 | ||
608 | Chip-specific information, e.g. the I/O port address, its resource | |
609 | pointer, or the irq number, is stored in the chip-specific record. | |
610 | ||
611 | :: | |
612 | ||
613 | struct mychip { | |
614 | .... | |
615 | }; | |
616 | ||
617 | ||
618 | In general, there are two ways of allocating the chip record. | |
619 | ||
620 | 1. Allocating via :c:func:`snd_card_new()`. | |
621 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
622 | ||
623 | As mentioned above, you can pass the extra-data-length to the 5th | |
624 | argument of :c:func:`snd_card_new()`, i.e. | |
625 | ||
626 | :: | |
627 | ||
628 | err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE, | |
629 | sizeof(struct mychip), &card); | |
630 | ||
631 | :c:type:`struct mychip <mychip>` is the type of the chip record. | |
632 | ||
633 | In return, the allocated record can be accessed as | |
634 | ||
635 | :: | |
636 | ||
637 | struct mychip *chip = card->private_data; | |
638 | ||
639 | With this method, you don't have to allocate twice. The record is | |
640 | released together with the card instance. | |
641 | ||
642 | 2. Allocating an extra device. | |
643 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
644 | ||
645 | After allocating a card instance via :c:func:`snd_card_new()` | |
646 | (with ``0`` on the 4th arg), call :c:func:`kzalloc()`. | |
647 | ||
648 | :: | |
649 | ||
650 | struct snd_card *card; | |
651 | struct mychip *chip; | |
652 | err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE, | |
653 | 0, &card); | |
654 | ..... | |
655 | chip = kzalloc(sizeof(*chip), GFP_KERNEL); | |
656 | ||
657 | The chip record should have the field to hold the card pointer at least, | |
658 | ||
659 | :: | |
660 | ||
661 | struct mychip { | |
662 | struct snd_card *card; | |
663 | .... | |
664 | }; | |
665 | ||
666 | ||
667 | Then, set the card pointer in the returned chip instance. | |
668 | ||
669 | :: | |
670 | ||
671 | chip->card = card; | |
672 | ||
673 | Next, initialize the fields, and register this chip record as a | |
674 | low-level device with a specified ``ops``, | |
675 | ||
676 | :: | |
677 | ||
678 | static struct snd_device_ops ops = { | |
679 | .dev_free = snd_mychip_dev_free, | |
680 | }; | |
681 | .... | |
682 | snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops); | |
683 | ||
684 | :c:func:`snd_mychip_dev_free()` is the device-destructor | |
685 | function, which will call the real destructor. | |
686 | ||
687 | :: | |
688 | ||
689 | static int snd_mychip_dev_free(struct snd_device *device) | |
690 | { | |
691 | return snd_mychip_free(device->device_data); | |
692 | } | |
693 | ||
694 | where :c:func:`snd_mychip_free()` is the real destructor. | |
695 | ||
f90afe79 TI |
696 | The demerit of this method is the obviously more amount of codes. |
697 | The merit is, however, you can trigger the own callback at registering | |
698 | and disconnecting the card via setting in snd_device_ops. | |
699 | About the registering and disconnecting the card, see the subsections | |
700 | below. | |
701 | ||
702 | ||
7ddedebb TI |
703 | Registration and Release |
704 | ------------------------ | |
705 | ||
706 | After all components are assigned, register the card instance by calling | |
707 | :c:func:`snd_card_register()`. Access to the device files is | |
708 | enabled at this point. That is, before | |
709 | :c:func:`snd_card_register()` is called, the components are safely | |
710 | inaccessible from external side. If this call fails, exit the probe | |
711 | function after releasing the card via :c:func:`snd_card_free()`. | |
712 | ||
713 | For releasing the card instance, you can call simply | |
714 | :c:func:`snd_card_free()`. As mentioned earlier, all components | |
715 | are released automatically by this call. | |
716 | ||
717 | For a device which allows hotplugging, you can use | |
718 | :c:func:`snd_card_free_when_closed()`. This one will postpone | |
719 | the destruction until all devices are closed. | |
720 | ||
721 | PCI Resource Management | |
722 | ======================= | |
723 | ||
724 | Full Code Example | |
725 | ----------------- | |
726 | ||
727 | In this section, we'll complete the chip-specific constructor, | |
728 | destructor and PCI entries. Example code is shown first, below. | |
729 | ||
730 | :: | |
731 | ||
732 | struct mychip { | |
733 | struct snd_card *card; | |
734 | struct pci_dev *pci; | |
735 | ||
736 | unsigned long port; | |
737 | int irq; | |
738 | }; | |
739 | ||
740 | static int snd_mychip_free(struct mychip *chip) | |
741 | { | |
742 | /* disable hardware here if any */ | |
743 | .... /* (not implemented in this document) */ | |
744 | ||
745 | /* release the irq */ | |
746 | if (chip->irq >= 0) | |
747 | free_irq(chip->irq, chip); | |
748 | /* release the I/O ports & memory */ | |
749 | pci_release_regions(chip->pci); | |
750 | /* disable the PCI entry */ | |
751 | pci_disable_device(chip->pci); | |
752 | /* release the data */ | |
753 | kfree(chip); | |
754 | return 0; | |
755 | } | |
756 | ||
757 | /* chip-specific constructor */ | |
758 | static int snd_mychip_create(struct snd_card *card, | |
759 | struct pci_dev *pci, | |
760 | struct mychip **rchip) | |
761 | { | |
762 | struct mychip *chip; | |
763 | int err; | |
764 | static struct snd_device_ops ops = { | |
765 | .dev_free = snd_mychip_dev_free, | |
766 | }; | |
767 | ||
768 | *rchip = NULL; | |
769 | ||
770 | /* initialize the PCI entry */ | |
771 | err = pci_enable_device(pci); | |
772 | if (err < 0) | |
773 | return err; | |
774 | /* check PCI availability (28bit DMA) */ | |
775 | if (pci_set_dma_mask(pci, DMA_BIT_MASK(28)) < 0 || | |
776 | pci_set_consistent_dma_mask(pci, DMA_BIT_MASK(28)) < 0) { | |
777 | printk(KERN_ERR "error to set 28bit mask DMA\n"); | |
778 | pci_disable_device(pci); | |
779 | return -ENXIO; | |
780 | } | |
781 | ||
782 | chip = kzalloc(sizeof(*chip), GFP_KERNEL); | |
783 | if (chip == NULL) { | |
784 | pci_disable_device(pci); | |
785 | return -ENOMEM; | |
786 | } | |
787 | ||
788 | /* initialize the stuff */ | |
789 | chip->card = card; | |
790 | chip->pci = pci; | |
791 | chip->irq = -1; | |
792 | ||
793 | /* (1) PCI resource allocation */ | |
794 | err = pci_request_regions(pci, "My Chip"); | |
795 | if (err < 0) { | |
796 | kfree(chip); | |
797 | pci_disable_device(pci); | |
798 | return err; | |
799 | } | |
800 | chip->port = pci_resource_start(pci, 0); | |
801 | if (request_irq(pci->irq, snd_mychip_interrupt, | |
802 | IRQF_SHARED, KBUILD_MODNAME, chip)) { | |
803 | printk(KERN_ERR "cannot grab irq %d\n", pci->irq); | |
804 | snd_mychip_free(chip); | |
805 | return -EBUSY; | |
806 | } | |
807 | chip->irq = pci->irq; | |
94722e74 | 808 | card->sync_irq = chip->irq; |
7ddedebb TI |
809 | |
810 | /* (2) initialization of the chip hardware */ | |
811 | .... /* (not implemented in this document) */ | |
812 | ||
813 | err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops); | |
814 | if (err < 0) { | |
815 | snd_mychip_free(chip); | |
816 | return err; | |
817 | } | |
818 | ||
819 | *rchip = chip; | |
820 | return 0; | |
821 | } | |
822 | ||
823 | /* PCI IDs */ | |
824 | static struct pci_device_id snd_mychip_ids[] = { | |
825 | { PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR, | |
826 | PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, }, | |
827 | .... | |
828 | { 0, } | |
829 | }; | |
830 | MODULE_DEVICE_TABLE(pci, snd_mychip_ids); | |
831 | ||
832 | /* pci_driver definition */ | |
833 | static struct pci_driver driver = { | |
834 | .name = KBUILD_MODNAME, | |
835 | .id_table = snd_mychip_ids, | |
836 | .probe = snd_mychip_probe, | |
837 | .remove = snd_mychip_remove, | |
838 | }; | |
839 | ||
840 | /* module initialization */ | |
841 | static int __init alsa_card_mychip_init(void) | |
842 | { | |
843 | return pci_register_driver(&driver); | |
844 | } | |
845 | ||
846 | /* module clean up */ | |
847 | static void __exit alsa_card_mychip_exit(void) | |
848 | { | |
849 | pci_unregister_driver(&driver); | |
850 | } | |
851 | ||
852 | module_init(alsa_card_mychip_init) | |
853 | module_exit(alsa_card_mychip_exit) | |
854 | ||
855 | EXPORT_NO_SYMBOLS; /* for old kernels only */ | |
856 | ||
857 | Some Hafta's | |
858 | ------------ | |
859 | ||
860 | The allocation of PCI resources is done in the ``probe`` function, and | |
861 | usually an extra :c:func:`xxx_create()` function is written for this | |
862 | purpose. | |
863 | ||
864 | In the case of PCI devices, you first have to call the | |
865 | :c:func:`pci_enable_device()` function before allocating | |
866 | resources. Also, you need to set the proper PCI DMA mask to limit the | |
867 | accessed I/O range. In some cases, you might need to call | |
868 | :c:func:`pci_set_master()` function, too. | |
869 | ||
870 | Suppose the 28bit mask, and the code to be added would be like: | |
871 | ||
872 | :: | |
873 | ||
874 | err = pci_enable_device(pci); | |
875 | if (err < 0) | |
876 | return err; | |
877 | if (pci_set_dma_mask(pci, DMA_BIT_MASK(28)) < 0 || | |
878 | pci_set_consistent_dma_mask(pci, DMA_BIT_MASK(28)) < 0) { | |
879 | printk(KERN_ERR "error to set 28bit mask DMA\n"); | |
880 | pci_disable_device(pci); | |
881 | return -ENXIO; | |
882 | } | |
883 | ||
884 | ||
885 | Resource Allocation | |
886 | ------------------- | |
887 | ||
888 | The allocation of I/O ports and irqs is done via standard kernel | |
f90afe79 TI |
889 | functions. These resources must be released in the destructor |
890 | function (see below). | |
7ddedebb TI |
891 | |
892 | Now assume that the PCI device has an I/O port with 8 bytes and an | |
893 | interrupt. Then :c:type:`struct mychip <mychip>` will have the | |
894 | following fields: | |
895 | ||
896 | :: | |
897 | ||
898 | struct mychip { | |
899 | struct snd_card *card; | |
900 | ||
901 | unsigned long port; | |
902 | int irq; | |
903 | }; | |
904 | ||
905 | ||
906 | For an I/O port (and also a memory region), you need to have the | |
907 | resource pointer for the standard resource management. For an irq, you | |
908 | have to keep only the irq number (integer). But you need to initialize | |
909 | this number as -1 before actual allocation, since irq 0 is valid. The | |
910 | port address and its resource pointer can be initialized as null by | |
911 | :c:func:`kzalloc()` automatically, so you don't have to take care of | |
912 | resetting them. | |
913 | ||
914 | The allocation of an I/O port is done like this: | |
915 | ||
916 | :: | |
917 | ||
918 | err = pci_request_regions(pci, "My Chip"); | |
919 | if (err < 0) { | |
920 | kfree(chip); | |
921 | pci_disable_device(pci); | |
922 | return err; | |
923 | } | |
924 | chip->port = pci_resource_start(pci, 0); | |
925 | ||
926 | It will reserve the I/O port region of 8 bytes of the given PCI device. | |
927 | The returned value, ``chip->res_port``, is allocated via | |
928 | :c:func:`kmalloc()` by :c:func:`request_region()`. The pointer | |
929 | must be released via :c:func:`kfree()`, but there is a problem with | |
930 | this. This issue will be explained later. | |
931 | ||
932 | The allocation of an interrupt source is done like this: | |
933 | ||
934 | :: | |
935 | ||
936 | if (request_irq(pci->irq, snd_mychip_interrupt, | |
937 | IRQF_SHARED, KBUILD_MODNAME, chip)) { | |
938 | printk(KERN_ERR "cannot grab irq %d\n", pci->irq); | |
939 | snd_mychip_free(chip); | |
940 | return -EBUSY; | |
941 | } | |
942 | chip->irq = pci->irq; | |
943 | ||
944 | where :c:func:`snd_mychip_interrupt()` is the interrupt handler | |
945 | defined `later <#pcm-interface-interrupt-handler>`__. Note that | |
946 | ``chip->irq`` should be defined only when :c:func:`request_irq()` | |
947 | succeeded. | |
948 | ||
949 | On the PCI bus, interrupts can be shared. Thus, ``IRQF_SHARED`` is used | |
950 | as the interrupt flag of :c:func:`request_irq()`. | |
951 | ||
952 | The last argument of :c:func:`request_irq()` is the data pointer | |
953 | passed to the interrupt handler. Usually, the chip-specific record is | |
954 | used for that, but you can use what you like, too. | |
955 | ||
956 | I won't give details about the interrupt handler at this point, but at | |
957 | least its appearance can be explained now. The interrupt handler looks | |
958 | usually like the following: | |
959 | ||
960 | :: | |
961 | ||
962 | static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id) | |
963 | { | |
964 | struct mychip *chip = dev_id; | |
965 | .... | |
966 | return IRQ_HANDLED; | |
967 | } | |
968 | ||
94722e74 TI |
969 | After requesting the IRQ, you can passed it to ``card->sync_irq`` |
970 | field: | |
971 | :: | |
972 | ||
973 | card->irq = chip->irq; | |
974 | ||
975 | This allows PCM core automatically performing | |
976 | :c:func:`synchronize_irq()` at the necessary timing like ``hw_free``. | |
977 | See the later section `sync_stop callback`_ for details. | |
7ddedebb TI |
978 | |
979 | Now let's write the corresponding destructor for the resources above. | |
980 | The role of destructor is simple: disable the hardware (if already | |
981 | activated) and release the resources. So far, we have no hardware part, | |
982 | so the disabling code is not written here. | |
983 | ||
984 | To release the resources, the “check-and-release” method is a safer way. | |
985 | For the interrupt, do like this: | |
986 | ||
987 | :: | |
988 | ||
989 | if (chip->irq >= 0) | |
990 | free_irq(chip->irq, chip); | |
991 | ||
992 | Since the irq number can start from 0, you should initialize | |
993 | ``chip->irq`` with a negative value (e.g. -1), so that you can check | |
994 | the validity of the irq number as above. | |
995 | ||
996 | When you requested I/O ports or memory regions via | |
997 | :c:func:`pci_request_region()` or | |
998 | :c:func:`pci_request_regions()` like in this example, release the | |
999 | resource(s) using the corresponding function, | |
1000 | :c:func:`pci_release_region()` or | |
1001 | :c:func:`pci_release_regions()`. | |
1002 | ||
1003 | :: | |
1004 | ||
1005 | pci_release_regions(chip->pci); | |
1006 | ||
1007 | When you requested manually via :c:func:`request_region()` or | |
1008 | :c:func:`request_mem_region()`, you can release it via | |
1009 | :c:func:`release_resource()`. Suppose that you keep the resource | |
1010 | pointer returned from :c:func:`request_region()` in | |
1011 | chip->res_port, the release procedure looks like: | |
1012 | ||
1013 | :: | |
1014 | ||
1015 | release_and_free_resource(chip->res_port); | |
1016 | ||
1017 | Don't forget to call :c:func:`pci_disable_device()` before the | |
1018 | end. | |
1019 | ||
1020 | And finally, release the chip-specific record. | |
1021 | ||
1022 | :: | |
1023 | ||
1024 | kfree(chip); | |
1025 | ||
1026 | We didn't implement the hardware disabling part in the above. If you | |
1027 | need to do this, please note that the destructor may be called even | |
1028 | before the initialization of the chip is completed. It would be better | |
1029 | to have a flag to skip hardware disabling if the hardware was not | |
1030 | initialized yet. | |
1031 | ||
1032 | When the chip-data is assigned to the card using | |
1033 | :c:func:`snd_device_new()` with ``SNDRV_DEV_LOWLELVEL`` , its | |
1034 | destructor is called at the last. That is, it is assured that all other | |
1035 | components like PCMs and controls have already been released. You don't | |
1036 | have to stop PCMs, etc. explicitly, but just call low-level hardware | |
1037 | stopping. | |
1038 | ||
1039 | The management of a memory-mapped region is almost as same as the | |
1040 | management of an I/O port. You'll need three fields like the | |
1041 | following: | |
1042 | ||
1043 | :: | |
1044 | ||
1045 | struct mychip { | |
1046 | .... | |
1047 | unsigned long iobase_phys; | |
1048 | void __iomem *iobase_virt; | |
1049 | }; | |
1050 | ||
1051 | and the allocation would be like below: | |
1052 | ||
1053 | :: | |
1054 | ||
f90afe79 TI |
1055 | err = pci_request_regions(pci, "My Chip"); |
1056 | if (err < 0) { | |
7ddedebb TI |
1057 | kfree(chip); |
1058 | return err; | |
1059 | } | |
1060 | chip->iobase_phys = pci_resource_start(pci, 0); | |
4bdc0d67 | 1061 | chip->iobase_virt = ioremap(chip->iobase_phys, |
7ddedebb TI |
1062 | pci_resource_len(pci, 0)); |
1063 | ||
1064 | and the corresponding destructor would be: | |
1065 | ||
1066 | :: | |
1067 | ||
1068 | static int snd_mychip_free(struct mychip *chip) | |
1069 | { | |
1070 | .... | |
1071 | if (chip->iobase_virt) | |
1072 | iounmap(chip->iobase_virt); | |
1073 | .... | |
1074 | pci_release_regions(chip->pci); | |
1075 | .... | |
1076 | } | |
1077 | ||
f90afe79 TI |
1078 | Of course, a modern way with :c:func:`pci_iomap()` will make things a |
1079 | bit easier, too. | |
1080 | ||
1081 | :: | |
1082 | ||
1083 | err = pci_request_regions(pci, "My Chip"); | |
1084 | if (err < 0) { | |
1085 | kfree(chip); | |
1086 | return err; | |
1087 | } | |
1088 | chip->iobase_virt = pci_iomap(pci, 0, 0); | |
1089 | ||
1090 | which is paired with :c:func:`pci_iounmap()` at destructor. | |
1091 | ||
1092 | ||
7ddedebb TI |
1093 | PCI Entries |
1094 | ----------- | |
1095 | ||
1096 | So far, so good. Let's finish the missing PCI stuff. At first, we need a | |
1097 | :c:type:`struct pci_device_id <pci_device_id>` table for | |
1098 | this chipset. It's a table of PCI vendor/device ID number, and some | |
1099 | masks. | |
1100 | ||
1101 | For example, | |
1102 | ||
1103 | :: | |
1104 | ||
1105 | static struct pci_device_id snd_mychip_ids[] = { | |
1106 | { PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR, | |
1107 | PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, }, | |
1108 | .... | |
1109 | { 0, } | |
1110 | }; | |
1111 | MODULE_DEVICE_TABLE(pci, snd_mychip_ids); | |
1112 | ||
1113 | The first and second fields of the :c:type:`struct pci_device_id | |
1114 | <pci_device_id>` structure are the vendor and device IDs. If you | |
1115 | have no reason to filter the matching devices, you can leave the | |
1116 | remaining fields as above. The last field of the :c:type:`struct | |
1117 | pci_device_id <pci_device_id>` struct contains private data | |
1118 | for this entry. You can specify any value here, for example, to define | |
1119 | specific operations for supported device IDs. Such an example is found | |
1120 | in the intel8x0 driver. | |
1121 | ||
1122 | The last entry of this list is the terminator. You must specify this | |
1123 | all-zero entry. | |
1124 | ||
1125 | Then, prepare the :c:type:`struct pci_driver <pci_driver>` | |
1126 | record: | |
1127 | ||
1128 | :: | |
1129 | ||
1130 | static struct pci_driver driver = { | |
1131 | .name = KBUILD_MODNAME, | |
1132 | .id_table = snd_mychip_ids, | |
1133 | .probe = snd_mychip_probe, | |
1134 | .remove = snd_mychip_remove, | |
1135 | }; | |
1136 | ||
1137 | The ``probe`` and ``remove`` functions have already been defined in | |
1138 | the previous sections. The ``name`` field is the name string of this | |
1139 | device. Note that you must not use a slash “/” in this string. | |
1140 | ||
1141 | And at last, the module entries: | |
1142 | ||
1143 | :: | |
1144 | ||
1145 | static int __init alsa_card_mychip_init(void) | |
1146 | { | |
1147 | return pci_register_driver(&driver); | |
1148 | } | |
1149 | ||
1150 | static void __exit alsa_card_mychip_exit(void) | |
1151 | { | |
1152 | pci_unregister_driver(&driver); | |
1153 | } | |
1154 | ||
1155 | module_init(alsa_card_mychip_init) | |
1156 | module_exit(alsa_card_mychip_exit) | |
1157 | ||
1158 | Note that these module entries are tagged with ``__init`` and ``__exit`` | |
1159 | prefixes. | |
1160 | ||
7ddedebb TI |
1161 | That's all! |
1162 | ||
1163 | PCM Interface | |
1164 | ============= | |
1165 | ||
1166 | General | |
1167 | ------- | |
1168 | ||
1169 | The PCM middle layer of ALSA is quite powerful and it is only necessary | |
1170 | for each driver to implement the low-level functions to access its | |
1171 | hardware. | |
1172 | ||
1173 | For accessing to the PCM layer, you need to include ``<sound/pcm.h>`` | |
1174 | first. In addition, ``<sound/pcm_params.h>`` might be needed if you | |
1175 | access to some functions related with hw_param. | |
1176 | ||
1177 | Each card device can have up to four pcm instances. A pcm instance | |
1178 | corresponds to a pcm device file. The limitation of number of instances | |
1179 | comes only from the available bit size of the Linux's device numbers. | |
1180 | Once when 64bit device number is used, we'll have more pcm instances | |
1181 | available. | |
1182 | ||
1183 | A pcm instance consists of pcm playback and capture streams, and each | |
1184 | pcm stream consists of one or more pcm substreams. Some soundcards | |
1185 | support multiple playback functions. For example, emu10k1 has a PCM | |
1186 | playback of 32 stereo substreams. In this case, at each open, a free | |
1187 | substream is (usually) automatically chosen and opened. Meanwhile, when | |
1188 | only one substream exists and it was already opened, the successful open | |
1189 | will either block or error with ``EAGAIN`` according to the file open | |
1190 | mode. But you don't have to care about such details in your driver. The | |
1191 | PCM middle layer will take care of such work. | |
1192 | ||
1193 | Full Code Example | |
1194 | ----------------- | |
1195 | ||
1196 | The example code below does not include any hardware access routines but | |
1197 | shows only the skeleton, how to build up the PCM interfaces. | |
1198 | ||
1199 | :: | |
1200 | ||
1201 | #include <sound/pcm.h> | |
1202 | .... | |
1203 | ||
1204 | /* hardware definition */ | |
1205 | static struct snd_pcm_hardware snd_mychip_playback_hw = { | |
1206 | .info = (SNDRV_PCM_INFO_MMAP | | |
1207 | SNDRV_PCM_INFO_INTERLEAVED | | |
1208 | SNDRV_PCM_INFO_BLOCK_TRANSFER | | |
1209 | SNDRV_PCM_INFO_MMAP_VALID), | |
1210 | .formats = SNDRV_PCM_FMTBIT_S16_LE, | |
1211 | .rates = SNDRV_PCM_RATE_8000_48000, | |
1212 | .rate_min = 8000, | |
1213 | .rate_max = 48000, | |
1214 | .channels_min = 2, | |
1215 | .channels_max = 2, | |
1216 | .buffer_bytes_max = 32768, | |
1217 | .period_bytes_min = 4096, | |
1218 | .period_bytes_max = 32768, | |
1219 | .periods_min = 1, | |
1220 | .periods_max = 1024, | |
1221 | }; | |
1222 | ||
1223 | /* hardware definition */ | |
1224 | static struct snd_pcm_hardware snd_mychip_capture_hw = { | |
1225 | .info = (SNDRV_PCM_INFO_MMAP | | |
1226 | SNDRV_PCM_INFO_INTERLEAVED | | |
1227 | SNDRV_PCM_INFO_BLOCK_TRANSFER | | |
1228 | SNDRV_PCM_INFO_MMAP_VALID), | |
1229 | .formats = SNDRV_PCM_FMTBIT_S16_LE, | |
1230 | .rates = SNDRV_PCM_RATE_8000_48000, | |
1231 | .rate_min = 8000, | |
1232 | .rate_max = 48000, | |
1233 | .channels_min = 2, | |
1234 | .channels_max = 2, | |
1235 | .buffer_bytes_max = 32768, | |
1236 | .period_bytes_min = 4096, | |
1237 | .period_bytes_max = 32768, | |
1238 | .periods_min = 1, | |
1239 | .periods_max = 1024, | |
1240 | }; | |
1241 | ||
1242 | /* open callback */ | |
1243 | static int snd_mychip_playback_open(struct snd_pcm_substream *substream) | |
1244 | { | |
1245 | struct mychip *chip = snd_pcm_substream_chip(substream); | |
1246 | struct snd_pcm_runtime *runtime = substream->runtime; | |
1247 | ||
1248 | runtime->hw = snd_mychip_playback_hw; | |
1249 | /* more hardware-initialization will be done here */ | |
1250 | .... | |
1251 | return 0; | |
1252 | } | |
1253 | ||
1254 | /* close callback */ | |
1255 | static int snd_mychip_playback_close(struct snd_pcm_substream *substream) | |
1256 | { | |
1257 | struct mychip *chip = snd_pcm_substream_chip(substream); | |
1258 | /* the hardware-specific codes will be here */ | |
1259 | .... | |
1260 | return 0; | |
1261 | ||
1262 | } | |
1263 | ||
1264 | /* open callback */ | |
1265 | static int snd_mychip_capture_open(struct snd_pcm_substream *substream) | |
1266 | { | |
1267 | struct mychip *chip = snd_pcm_substream_chip(substream); | |
1268 | struct snd_pcm_runtime *runtime = substream->runtime; | |
1269 | ||
1270 | runtime->hw = snd_mychip_capture_hw; | |
1271 | /* more hardware-initialization will be done here */ | |
1272 | .... | |
1273 | return 0; | |
1274 | } | |
1275 | ||
1276 | /* close callback */ | |
1277 | static int snd_mychip_capture_close(struct snd_pcm_substream *substream) | |
1278 | { | |
1279 | struct mychip *chip = snd_pcm_substream_chip(substream); | |
1280 | /* the hardware-specific codes will be here */ | |
1281 | .... | |
1282 | return 0; | |
7ddedebb TI |
1283 | } |
1284 | ||
1285 | /* hw_params callback */ | |
1286 | static int snd_mychip_pcm_hw_params(struct snd_pcm_substream *substream, | |
1287 | struct snd_pcm_hw_params *hw_params) | |
1288 | { | |
72b4bcbf TI |
1289 | /* the hardware-specific codes will be here */ |
1290 | .... | |
1291 | return 0; | |
7ddedebb TI |
1292 | } |
1293 | ||
1294 | /* hw_free callback */ | |
1295 | static int snd_mychip_pcm_hw_free(struct snd_pcm_substream *substream) | |
1296 | { | |
72b4bcbf TI |
1297 | /* the hardware-specific codes will be here */ |
1298 | .... | |
1299 | return 0; | |
7ddedebb TI |
1300 | } |
1301 | ||
1302 | /* prepare callback */ | |
1303 | static int snd_mychip_pcm_prepare(struct snd_pcm_substream *substream) | |
1304 | { | |
1305 | struct mychip *chip = snd_pcm_substream_chip(substream); | |
1306 | struct snd_pcm_runtime *runtime = substream->runtime; | |
1307 | ||
1308 | /* set up the hardware with the current configuration | |
1309 | * for example... | |
1310 | */ | |
1311 | mychip_set_sample_format(chip, runtime->format); | |
1312 | mychip_set_sample_rate(chip, runtime->rate); | |
1313 | mychip_set_channels(chip, runtime->channels); | |
1314 | mychip_set_dma_setup(chip, runtime->dma_addr, | |
1315 | chip->buffer_size, | |
1316 | chip->period_size); | |
1317 | return 0; | |
1318 | } | |
1319 | ||
1320 | /* trigger callback */ | |
1321 | static int snd_mychip_pcm_trigger(struct snd_pcm_substream *substream, | |
1322 | int cmd) | |
1323 | { | |
1324 | switch (cmd) { | |
1325 | case SNDRV_PCM_TRIGGER_START: | |
1326 | /* do something to start the PCM engine */ | |
1327 | .... | |
1328 | break; | |
1329 | case SNDRV_PCM_TRIGGER_STOP: | |
1330 | /* do something to stop the PCM engine */ | |
1331 | .... | |
1332 | break; | |
1333 | default: | |
1334 | return -EINVAL; | |
1335 | } | |
1336 | } | |
1337 | ||
1338 | /* pointer callback */ | |
1339 | static snd_pcm_uframes_t | |
1340 | snd_mychip_pcm_pointer(struct snd_pcm_substream *substream) | |
1341 | { | |
1342 | struct mychip *chip = snd_pcm_substream_chip(substream); | |
1343 | unsigned int current_ptr; | |
1344 | ||
1345 | /* get the current hardware pointer */ | |
1346 | current_ptr = mychip_get_hw_pointer(chip); | |
1347 | return current_ptr; | |
1348 | } | |
1349 | ||
1350 | /* operators */ | |
1351 | static struct snd_pcm_ops snd_mychip_playback_ops = { | |
1352 | .open = snd_mychip_playback_open, | |
1353 | .close = snd_mychip_playback_close, | |
7ddedebb TI |
1354 | .hw_params = snd_mychip_pcm_hw_params, |
1355 | .hw_free = snd_mychip_pcm_hw_free, | |
1356 | .prepare = snd_mychip_pcm_prepare, | |
1357 | .trigger = snd_mychip_pcm_trigger, | |
1358 | .pointer = snd_mychip_pcm_pointer, | |
1359 | }; | |
1360 | ||
1361 | /* operators */ | |
1362 | static struct snd_pcm_ops snd_mychip_capture_ops = { | |
1363 | .open = snd_mychip_capture_open, | |
1364 | .close = snd_mychip_capture_close, | |
7ddedebb TI |
1365 | .hw_params = snd_mychip_pcm_hw_params, |
1366 | .hw_free = snd_mychip_pcm_hw_free, | |
1367 | .prepare = snd_mychip_pcm_prepare, | |
1368 | .trigger = snd_mychip_pcm_trigger, | |
1369 | .pointer = snd_mychip_pcm_pointer, | |
1370 | }; | |
1371 | ||
1372 | /* | |
1373 | * definitions of capture are omitted here... | |
1374 | */ | |
1375 | ||
1376 | /* create a pcm device */ | |
1377 | static int snd_mychip_new_pcm(struct mychip *chip) | |
1378 | { | |
1379 | struct snd_pcm *pcm; | |
1380 | int err; | |
1381 | ||
1382 | err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm); | |
1383 | if (err < 0) | |
1384 | return err; | |
1385 | pcm->private_data = chip; | |
1386 | strcpy(pcm->name, "My Chip"); | |
1387 | chip->pcm = pcm; | |
1388 | /* set operators */ | |
1389 | snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, | |
1390 | &snd_mychip_playback_ops); | |
1391 | snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE, | |
1392 | &snd_mychip_capture_ops); | |
1393 | /* pre-allocation of buffers */ | |
1394 | /* NOTE: this may fail */ | |
72b4bcbf TI |
1395 | snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_DEV, |
1396 | &chip->pci->dev, | |
1397 | 64*1024, 64*1024); | |
7ddedebb TI |
1398 | return 0; |
1399 | } | |
1400 | ||
1401 | ||
1402 | PCM Constructor | |
1403 | --------------- | |
1404 | ||
1405 | A pcm instance is allocated by the :c:func:`snd_pcm_new()` | |
1406 | function. It would be better to create a constructor for pcm, namely, | |
1407 | ||
1408 | :: | |
1409 | ||
1410 | static int snd_mychip_new_pcm(struct mychip *chip) | |
1411 | { | |
1412 | struct snd_pcm *pcm; | |
1413 | int err; | |
1414 | ||
1415 | err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm); | |
1416 | if (err < 0) | |
1417 | return err; | |
1418 | pcm->private_data = chip; | |
1419 | strcpy(pcm->name, "My Chip"); | |
1420 | chip->pcm = pcm; | |
1421 | .... | |
1422 | return 0; | |
1423 | } | |
1424 | ||
1425 | The :c:func:`snd_pcm_new()` function takes four arguments. The | |
1426 | first argument is the card pointer to which this pcm is assigned, and | |
1427 | the second is the ID string. | |
1428 | ||
1429 | The third argument (``index``, 0 in the above) is the index of this new | |
1430 | pcm. It begins from zero. If you create more than one pcm instances, | |
1431 | specify the different numbers in this argument. For example, ``index = | |
1432 | 1`` for the second PCM device. | |
1433 | ||
1434 | The fourth and fifth arguments are the number of substreams for playback | |
1435 | and capture, respectively. Here 1 is used for both arguments. When no | |
1436 | playback or capture substreams are available, pass 0 to the | |
1437 | corresponding argument. | |
1438 | ||
1439 | If a chip supports multiple playbacks or captures, you can specify more | |
1440 | numbers, but they must be handled properly in open/close, etc. | |
1441 | callbacks. When you need to know which substream you are referring to, | |
1442 | then it can be obtained from :c:type:`struct snd_pcm_substream | |
1443 | <snd_pcm_substream>` data passed to each callback as follows: | |
1444 | ||
1445 | :: | |
1446 | ||
1447 | struct snd_pcm_substream *substream; | |
1448 | int index = substream->number; | |
1449 | ||
1450 | ||
1451 | After the pcm is created, you need to set operators for each pcm stream. | |
1452 | ||
1453 | :: | |
1454 | ||
1455 | snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, | |
1456 | &snd_mychip_playback_ops); | |
1457 | snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE, | |
1458 | &snd_mychip_capture_ops); | |
1459 | ||
1460 | The operators are defined typically like this: | |
1461 | ||
1462 | :: | |
1463 | ||
1464 | static struct snd_pcm_ops snd_mychip_playback_ops = { | |
1465 | .open = snd_mychip_pcm_open, | |
1466 | .close = snd_mychip_pcm_close, | |
7ddedebb TI |
1467 | .hw_params = snd_mychip_pcm_hw_params, |
1468 | .hw_free = snd_mychip_pcm_hw_free, | |
1469 | .prepare = snd_mychip_pcm_prepare, | |
1470 | .trigger = snd_mychip_pcm_trigger, | |
1471 | .pointer = snd_mychip_pcm_pointer, | |
1472 | }; | |
1473 | ||
1474 | All the callbacks are described in the Operators_ subsection. | |
1475 | ||
1476 | After setting the operators, you probably will want to pre-allocate the | |
72b4bcbf TI |
1477 | buffer and set up the managed allocation mode. |
1478 | For that, simply call the following: | |
7ddedebb TI |
1479 | |
1480 | :: | |
1481 | ||
72b4bcbf TI |
1482 | snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_DEV, |
1483 | &chip->pci->dev, | |
1484 | 64*1024, 64*1024); | |
7ddedebb TI |
1485 | |
1486 | It will allocate a buffer up to 64kB as default. Buffer management | |
1487 | details will be described in the later section `Buffer and Memory | |
1488 | Management`_. | |
1489 | ||
1490 | Additionally, you can set some extra information for this pcm in | |
1491 | ``pcm->info_flags``. The available values are defined as | |
1492 | ``SNDRV_PCM_INFO_XXX`` in ``<sound/asound.h>``, which is used for the | |
1493 | hardware definition (described later). When your soundchip supports only | |
1494 | half-duplex, specify like this: | |
1495 | ||
1496 | :: | |
1497 | ||
1498 | pcm->info_flags = SNDRV_PCM_INFO_HALF_DUPLEX; | |
1499 | ||
1500 | ||
1501 | ... And the Destructor? | |
1502 | ----------------------- | |
1503 | ||
1504 | The destructor for a pcm instance is not always necessary. Since the pcm | |
1505 | device will be released by the middle layer code automatically, you | |
1506 | don't have to call the destructor explicitly. | |
1507 | ||
1508 | The destructor would be necessary if you created special records | |
1509 | internally and needed to release them. In such a case, set the | |
1510 | destructor function to ``pcm->private_free``: | |
1511 | ||
1512 | :: | |
1513 | ||
1514 | static void mychip_pcm_free(struct snd_pcm *pcm) | |
1515 | { | |
1516 | struct mychip *chip = snd_pcm_chip(pcm); | |
1517 | /* free your own data */ | |
1518 | kfree(chip->my_private_pcm_data); | |
1519 | /* do what you like else */ | |
1520 | .... | |
1521 | } | |
1522 | ||
1523 | static int snd_mychip_new_pcm(struct mychip *chip) | |
1524 | { | |
1525 | struct snd_pcm *pcm; | |
1526 | .... | |
1527 | /* allocate your own data */ | |
1528 | chip->my_private_pcm_data = kmalloc(...); | |
1529 | /* set the destructor */ | |
1530 | pcm->private_data = chip; | |
1531 | pcm->private_free = mychip_pcm_free; | |
1532 | .... | |
1533 | } | |
1534 | ||
1535 | ||
1536 | ||
1537 | Runtime Pointer - The Chest of PCM Information | |
1538 | ---------------------------------------------- | |
1539 | ||
1540 | When the PCM substream is opened, a PCM runtime instance is allocated | |
1541 | and assigned to the substream. This pointer is accessible via | |
1542 | ``substream->runtime``. This runtime pointer holds most information you | |
1543 | need to control the PCM: the copy of hw_params and sw_params | |
1544 | configurations, the buffer pointers, mmap records, spinlocks, etc. | |
1545 | ||
1546 | The definition of runtime instance is found in ``<sound/pcm.h>``. Here | |
1547 | are the contents of this file: | |
1548 | ||
1549 | :: | |
1550 | ||
1551 | struct _snd_pcm_runtime { | |
1552 | /* -- Status -- */ | |
1553 | struct snd_pcm_substream *trigger_master; | |
1554 | snd_timestamp_t trigger_tstamp; /* trigger timestamp */ | |
1555 | int overrange; | |
1556 | snd_pcm_uframes_t avail_max; | |
1557 | snd_pcm_uframes_t hw_ptr_base; /* Position at buffer restart */ | |
1558 | snd_pcm_uframes_t hw_ptr_interrupt; /* Position at interrupt time*/ | |
1559 | ||
1560 | /* -- HW params -- */ | |
1561 | snd_pcm_access_t access; /* access mode */ | |
1562 | snd_pcm_format_t format; /* SNDRV_PCM_FORMAT_* */ | |
1563 | snd_pcm_subformat_t subformat; /* subformat */ | |
1564 | unsigned int rate; /* rate in Hz */ | |
1565 | unsigned int channels; /* channels */ | |
1566 | snd_pcm_uframes_t period_size; /* period size */ | |
1567 | unsigned int periods; /* periods */ | |
1568 | snd_pcm_uframes_t buffer_size; /* buffer size */ | |
1569 | unsigned int tick_time; /* tick time */ | |
1570 | snd_pcm_uframes_t min_align; /* Min alignment for the format */ | |
1571 | size_t byte_align; | |
1572 | unsigned int frame_bits; | |
1573 | unsigned int sample_bits; | |
1574 | unsigned int info; | |
1575 | unsigned int rate_num; | |
1576 | unsigned int rate_den; | |
1577 | ||
1578 | /* -- SW params -- */ | |
1579 | struct timespec tstamp_mode; /* mmap timestamp is updated */ | |
1580 | unsigned int period_step; | |
1581 | unsigned int sleep_min; /* min ticks to sleep */ | |
1582 | snd_pcm_uframes_t start_threshold; | |
1583 | snd_pcm_uframes_t stop_threshold; | |
1584 | snd_pcm_uframes_t silence_threshold; /* Silence filling happens when | |
1585 | noise is nearest than this */ | |
1586 | snd_pcm_uframes_t silence_size; /* Silence filling size */ | |
1587 | snd_pcm_uframes_t boundary; /* pointers wrap point */ | |
1588 | ||
1589 | snd_pcm_uframes_t silenced_start; | |
1590 | snd_pcm_uframes_t silenced_size; | |
1591 | ||
1592 | snd_pcm_sync_id_t sync; /* hardware synchronization ID */ | |
1593 | ||
1594 | /* -- mmap -- */ | |
1595 | volatile struct snd_pcm_mmap_status *status; | |
1596 | volatile struct snd_pcm_mmap_control *control; | |
1597 | atomic_t mmap_count; | |
1598 | ||
1599 | /* -- locking / scheduling -- */ | |
1600 | spinlock_t lock; | |
1601 | wait_queue_head_t sleep; | |
1602 | struct timer_list tick_timer; | |
1603 | struct fasync_struct *fasync; | |
1604 | ||
1605 | /* -- private section -- */ | |
1606 | void *private_data; | |
1607 | void (*private_free)(struct snd_pcm_runtime *runtime); | |
1608 | ||
1609 | /* -- hardware description -- */ | |
1610 | struct snd_pcm_hardware hw; | |
1611 | struct snd_pcm_hw_constraints hw_constraints; | |
1612 | ||
1613 | /* -- timer -- */ | |
1614 | unsigned int timer_resolution; /* timer resolution */ | |
1615 | ||
1616 | /* -- DMA -- */ | |
1617 | unsigned char *dma_area; /* DMA area */ | |
1618 | dma_addr_t dma_addr; /* physical bus address (not accessible from main CPU) */ | |
1619 | size_t dma_bytes; /* size of DMA area */ | |
1620 | ||
1621 | struct snd_dma_buffer *dma_buffer_p; /* allocated buffer */ | |
1622 | ||
1623 | #if defined(CONFIG_SND_PCM_OSS) || defined(CONFIG_SND_PCM_OSS_MODULE) | |
1624 | /* -- OSS things -- */ | |
1625 | struct snd_pcm_oss_runtime oss; | |
1626 | #endif | |
1627 | }; | |
1628 | ||
1629 | ||
1630 | For the operators (callbacks) of each sound driver, most of these | |
1631 | records are supposed to be read-only. Only the PCM middle-layer changes | |
1632 | / updates them. The exceptions are the hardware description (hw) DMA | |
1633 | buffer information and the private data. Besides, if you use the | |
72b4bcbf | 1634 | standard managed buffer allocation mode, you don't need to set the |
7ddedebb TI |
1635 | DMA buffer information by yourself. |
1636 | ||
1637 | In the sections below, important records are explained. | |
1638 | ||
1639 | Hardware Description | |
1640 | ~~~~~~~~~~~~~~~~~~~~ | |
1641 | ||
1642 | The hardware descriptor (:c:type:`struct snd_pcm_hardware | |
1643 | <snd_pcm_hardware>`) contains the definitions of the fundamental | |
1644 | hardware configuration. Above all, you'll need to define this in the | |
1645 | `PCM open callback`_. Note that the runtime instance holds the copy of | |
1646 | the descriptor, not the pointer to the existing descriptor. That is, | |
1647 | in the open callback, you can modify the copied descriptor | |
1648 | (``runtime->hw``) as you need. For example, if the maximum number of | |
1649 | channels is 1 only on some chip models, you can still use the same | |
1650 | hardware descriptor and change the channels_max later: | |
1651 | ||
1652 | :: | |
1653 | ||
1654 | struct snd_pcm_runtime *runtime = substream->runtime; | |
1655 | ... | |
1656 | runtime->hw = snd_mychip_playback_hw; /* common definition */ | |
1657 | if (chip->model == VERY_OLD_ONE) | |
1658 | runtime->hw.channels_max = 1; | |
1659 | ||
1660 | Typically, you'll have a hardware descriptor as below: | |
1661 | ||
1662 | :: | |
1663 | ||
1664 | static struct snd_pcm_hardware snd_mychip_playback_hw = { | |
1665 | .info = (SNDRV_PCM_INFO_MMAP | | |
1666 | SNDRV_PCM_INFO_INTERLEAVED | | |
1667 | SNDRV_PCM_INFO_BLOCK_TRANSFER | | |
1668 | SNDRV_PCM_INFO_MMAP_VALID), | |
1669 | .formats = SNDRV_PCM_FMTBIT_S16_LE, | |
1670 | .rates = SNDRV_PCM_RATE_8000_48000, | |
1671 | .rate_min = 8000, | |
1672 | .rate_max = 48000, | |
1673 | .channels_min = 2, | |
1674 | .channels_max = 2, | |
1675 | .buffer_bytes_max = 32768, | |
1676 | .period_bytes_min = 4096, | |
1677 | .period_bytes_max = 32768, | |
1678 | .periods_min = 1, | |
1679 | .periods_max = 1024, | |
1680 | }; | |
1681 | ||
1682 | - The ``info`` field contains the type and capabilities of this | |
1683 | pcm. The bit flags are defined in ``<sound/asound.h>`` as | |
1684 | ``SNDRV_PCM_INFO_XXX``. Here, at least, you have to specify whether | |
1685 | the mmap is supported and which interleaved format is | |
1686 | supported. When the hardware supports mmap, add the | |
1687 | ``SNDRV_PCM_INFO_MMAP`` flag here. When the hardware supports the | |
1688 | interleaved or the non-interleaved formats, | |
1689 | ``SNDRV_PCM_INFO_INTERLEAVED`` or ``SNDRV_PCM_INFO_NONINTERLEAVED`` | |
1690 | flag must be set, respectively. If both are supported, you can set | |
1691 | both, too. | |
1692 | ||
1693 | In the above example, ``MMAP_VALID`` and ``BLOCK_TRANSFER`` are | |
1694 | specified for the OSS mmap mode. Usually both are set. Of course, | |
1695 | ``MMAP_VALID`` is set only if the mmap is really supported. | |
1696 | ||
1697 | The other possible flags are ``SNDRV_PCM_INFO_PAUSE`` and | |
1698 | ``SNDRV_PCM_INFO_RESUME``. The ``PAUSE`` bit means that the pcm | |
1699 | supports the “pause” operation, while the ``RESUME`` bit means that | |
1700 | the pcm supports the full “suspend/resume” operation. If the | |
1701 | ``PAUSE`` flag is set, the ``trigger`` callback below must handle | |
1702 | the corresponding (pause push/release) commands. The suspend/resume | |
1703 | trigger commands can be defined even without the ``RESUME`` | |
1704 | flag. See `Power Management`_ section for details. | |
1705 | ||
1706 | When the PCM substreams can be synchronized (typically, | |
1707 | synchronized start/stop of a playback and a capture streams), you | |
1708 | can give ``SNDRV_PCM_INFO_SYNC_START``, too. In this case, you'll | |
1709 | need to check the linked-list of PCM substreams in the trigger | |
1710 | callback. This will be described in the later section. | |
1711 | ||
1712 | - ``formats`` field contains the bit-flags of supported formats | |
1713 | (``SNDRV_PCM_FMTBIT_XXX``). If the hardware supports more than one | |
1714 | format, give all or'ed bits. In the example above, the signed 16bit | |
1715 | little-endian format is specified. | |
1716 | ||
1717 | - ``rates`` field contains the bit-flags of supported rates | |
1718 | (``SNDRV_PCM_RATE_XXX``). When the chip supports continuous rates, | |
1719 | pass ``CONTINUOUS`` bit additionally. The pre-defined rate bits are | |
1720 | provided only for typical rates. If your chip supports | |
1721 | unconventional rates, you need to add the ``KNOT`` bit and set up | |
1722 | the hardware constraint manually (explained later). | |
1723 | ||
1724 | - ``rate_min`` and ``rate_max`` define the minimum and maximum sample | |
1725 | rate. This should correspond somehow to ``rates`` bits. | |
1726 | ||
1727 | - ``channel_min`` and ``channel_max`` define, as you might already | |
1728 | expected, the minimum and maximum number of channels. | |
1729 | ||
1730 | - ``buffer_bytes_max`` defines the maximum buffer size in | |
1731 | bytes. There is no ``buffer_bytes_min`` field, since it can be | |
1732 | calculated from the minimum period size and the minimum number of | |
1733 | periods. Meanwhile, ``period_bytes_min`` and define the minimum and | |
1734 | maximum size of the period in bytes. ``periods_max`` and | |
1735 | ``periods_min`` define the maximum and minimum number of periods in | |
1736 | the buffer. | |
1737 | ||
1738 | The “period” is a term that corresponds to a fragment in the OSS | |
1739 | world. The period defines the size at which a PCM interrupt is | |
1740 | generated. This size strongly depends on the hardware. Generally, | |
1741 | the smaller period size will give you more interrupts, that is, | |
1742 | more controls. In the case of capture, this size defines the input | |
1743 | latency. On the other hand, the whole buffer size defines the | |
1744 | output latency for the playback direction. | |
1745 | ||
1746 | - There is also a field ``fifo_size``. This specifies the size of the | |
1747 | hardware FIFO, but currently it is neither used in the driver nor | |
1748 | in the alsa-lib. So, you can ignore this field. | |
1749 | ||
1750 | PCM Configurations | |
1751 | ~~~~~~~~~~~~~~~~~~ | |
1752 | ||
1753 | Ok, let's go back again to the PCM runtime records. The most | |
1754 | frequently referred records in the runtime instance are the PCM | |
1755 | configurations. The PCM configurations are stored in the runtime | |
1756 | instance after the application sends ``hw_params`` data via | |
1757 | alsa-lib. There are many fields copied from hw_params and sw_params | |
1758 | structs. For example, ``format`` holds the format type chosen by the | |
1759 | application. This field contains the enum value | |
1760 | ``SNDRV_PCM_FORMAT_XXX``. | |
1761 | ||
1762 | One thing to be noted is that the configured buffer and period sizes | |
1763 | are stored in “frames” in the runtime. In the ALSA world, ``1 frame = | |
1764 | channels \* samples-size``. For conversion between frames and bytes, | |
1765 | you can use the :c:func:`frames_to_bytes()` and | |
1766 | :c:func:`bytes_to_frames()` helper functions. | |
1767 | ||
1768 | :: | |
1769 | ||
1770 | period_bytes = frames_to_bytes(runtime, runtime->period_size); | |
1771 | ||
1772 | Also, many software parameters (sw_params) are stored in frames, too. | |
1773 | Please check the type of the field. ``snd_pcm_uframes_t`` is for the | |
1774 | frames as unsigned integer while ``snd_pcm_sframes_t`` is for the | |
1775 | frames as signed integer. | |
1776 | ||
1777 | DMA Buffer Information | |
1778 | ~~~~~~~~~~~~~~~~~~~~~~ | |
1779 | ||
1780 | The DMA buffer is defined by the following four fields, ``dma_area``, | |
1781 | ``dma_addr``, ``dma_bytes`` and ``dma_private``. The ``dma_area`` | |
1782 | holds the buffer pointer (the logical address). You can call | |
1783 | :c:func:`memcpy()` from/to this pointer. Meanwhile, ``dma_addr`` holds | |
1784 | the physical address of the buffer. This field is specified only when | |
1785 | the buffer is a linear buffer. ``dma_bytes`` holds the size of buffer | |
1786 | in bytes. ``dma_private`` is used for the ALSA DMA allocator. | |
1787 | ||
72b4bcbf TI |
1788 | If you use either the managed buffer allocation mode or the standard |
1789 | API function :c:func:`snd_pcm_lib_malloc_pages()` for allocating the buffer, | |
7ddedebb TI |
1790 | these fields are set by the ALSA middle layer, and you should *not* |
1791 | change them by yourself. You can read them but not write them. On the | |
1792 | other hand, if you want to allocate the buffer by yourself, you'll | |
1793 | need to manage it in hw_params callback. At least, ``dma_bytes`` is | |
1794 | mandatory. ``dma_area`` is necessary when the buffer is mmapped. If | |
1795 | your driver doesn't support mmap, this field is not | |
1796 | necessary. ``dma_addr`` is also optional. You can use dma_private as | |
1797 | you like, too. | |
1798 | ||
1799 | Running Status | |
1800 | ~~~~~~~~~~~~~~ | |
1801 | ||
1802 | The running status can be referred via ``runtime->status``. This is | |
1803 | the pointer to the :c:type:`struct snd_pcm_mmap_status | |
1804 | <snd_pcm_mmap_status>` record. For example, you can get the current | |
1805 | DMA hardware pointer via ``runtime->status->hw_ptr``. | |
1806 | ||
1807 | The DMA application pointer can be referred via ``runtime->control``, | |
1808 | which points to the :c:type:`struct snd_pcm_mmap_control | |
1809 | <snd_pcm_mmap_control>` record. However, accessing directly to | |
1810 | this value is not recommended. | |
1811 | ||
1812 | Private Data | |
1813 | ~~~~~~~~~~~~ | |
1814 | ||
1815 | You can allocate a record for the substream and store it in | |
1816 | ``runtime->private_data``. Usually, this is done in the `PCM open | |
1817 | callback`_. Don't mix this with ``pcm->private_data``. The | |
1818 | ``pcm->private_data`` usually points to the chip instance assigned | |
1819 | statically at the creation of PCM, while the ``runtime->private_data`` | |
1820 | points to a dynamic data structure created at the PCM open | |
1821 | callback. | |
1822 | ||
1823 | :: | |
1824 | ||
1825 | static int snd_xxx_open(struct snd_pcm_substream *substream) | |
1826 | { | |
1827 | struct my_pcm_data *data; | |
1828 | .... | |
1829 | data = kmalloc(sizeof(*data), GFP_KERNEL); | |
1830 | substream->runtime->private_data = data; | |
1831 | .... | |
1832 | } | |
1833 | ||
1834 | ||
1835 | The allocated object must be released in the `close callback`_. | |
1836 | ||
1837 | Operators | |
1838 | --------- | |
1839 | ||
1840 | OK, now let me give details about each pcm callback (``ops``). In | |
1841 | general, every callback must return 0 if successful, or a negative | |
1842 | error number such as ``-EINVAL``. To choose an appropriate error | |
1843 | number, it is advised to check what value other parts of the kernel | |
1844 | return when the same kind of request fails. | |
1845 | ||
1846 | The callback function takes at least the argument with :c:type:`struct | |
1847 | snd_pcm_substream <snd_pcm_substream>` pointer. To retrieve the chip | |
1848 | record from the given substream instance, you can use the following | |
1849 | macro. | |
1850 | ||
1851 | :: | |
1852 | ||
1853 | int xxx() { | |
1854 | struct mychip *chip = snd_pcm_substream_chip(substream); | |
1855 | .... | |
1856 | } | |
1857 | ||
1858 | The macro reads ``substream->private_data``, which is a copy of | |
1859 | ``pcm->private_data``. You can override the former if you need to | |
1860 | assign different data records per PCM substream. For example, the | |
1861 | cmi8330 driver assigns different ``private_data`` for playback and | |
1862 | capture directions, because it uses two different codecs (SB- and | |
1863 | AD-compatible) for different directions. | |
1864 | ||
1865 | PCM open callback | |
1866 | ~~~~~~~~~~~~~~~~~ | |
1867 | ||
1868 | :: | |
1869 | ||
1870 | static int snd_xxx_open(struct snd_pcm_substream *substream); | |
1871 | ||
1872 | This is called when a pcm substream is opened. | |
1873 | ||
1874 | At least, here you have to initialize the ``runtime->hw`` | |
1875 | record. Typically, this is done by like this: | |
1876 | ||
1877 | :: | |
1878 | ||
1879 | static int snd_xxx_open(struct snd_pcm_substream *substream) | |
1880 | { | |
1881 | struct mychip *chip = snd_pcm_substream_chip(substream); | |
1882 | struct snd_pcm_runtime *runtime = substream->runtime; | |
1883 | ||
1884 | runtime->hw = snd_mychip_playback_hw; | |
1885 | return 0; | |
1886 | } | |
1887 | ||
1888 | where ``snd_mychip_playback_hw`` is the pre-defined hardware | |
1889 | description. | |
1890 | ||
1891 | You can allocate a private data in this callback, as described in | |
1892 | `Private Data`_ section. | |
1893 | ||
1894 | If the hardware configuration needs more constraints, set the hardware | |
1895 | constraints here, too. See Constraints_ for more details. | |
1896 | ||
1897 | close callback | |
1898 | ~~~~~~~~~~~~~~ | |
1899 | ||
1900 | :: | |
1901 | ||
1902 | static int snd_xxx_close(struct snd_pcm_substream *substream); | |
1903 | ||
1904 | ||
1905 | Obviously, this is called when a pcm substream is closed. | |
1906 | ||
1907 | Any private instance for a pcm substream allocated in the ``open`` | |
1908 | callback will be released here. | |
1909 | ||
1910 | :: | |
1911 | ||
1912 | static int snd_xxx_close(struct snd_pcm_substream *substream) | |
1913 | { | |
1914 | .... | |
1915 | kfree(substream->runtime->private_data); | |
1916 | .... | |
1917 | } | |
1918 | ||
1919 | ioctl callback | |
1920 | ~~~~~~~~~~~~~~ | |
1921 | ||
1922 | This is used for any special call to pcm ioctls. But usually you can | |
f6161f37 TI |
1923 | leave it as NULL, then PCM core calls the generic ioctl callback |
1924 | function :c:func:`snd_pcm_lib_ioctl()`. If you need to deal with the | |
1925 | unique setup of channel info or reset procedure, you can pass your own | |
1926 | callback function here. | |
7ddedebb TI |
1927 | |
1928 | hw_params callback | |
1929 | ~~~~~~~~~~~~~~~~~~~ | |
1930 | ||
1931 | :: | |
1932 | ||
1933 | static int snd_xxx_hw_params(struct snd_pcm_substream *substream, | |
1934 | struct snd_pcm_hw_params *hw_params); | |
1935 | ||
1936 | This is called when the hardware parameter (``hw_params``) is set up | |
1937 | by the application, that is, once when the buffer size, the period | |
1938 | size, the format, etc. are defined for the pcm substream. | |
1939 | ||
1940 | Many hardware setups should be done in this callback, including the | |
1941 | allocation of buffers. | |
1942 | ||
1943 | Parameters to be initialized are retrieved by | |
72b4bcbf TI |
1944 | :c:func:`params_xxx()` macros. |
1945 | ||
1946 | When you set up the managed buffer allocation mode for the substream, | |
1947 | a buffer is already allocated before this callback gets | |
1948 | called. Alternatively, you can call a helper function below for | |
1949 | allocating the buffer, too. | |
7ddedebb TI |
1950 | |
1951 | :: | |
1952 | ||
1953 | snd_pcm_lib_malloc_pages(substream, params_buffer_bytes(hw_params)); | |
1954 | ||
1955 | :c:func:`snd_pcm_lib_malloc_pages()` is available only when the | |
1956 | DMA buffers have been pre-allocated. See the section `Buffer Types`_ | |
1957 | for more details. | |
1958 | ||
1959 | Note that this and ``prepare`` callbacks may be called multiple times | |
1960 | per initialization. For example, the OSS emulation may call these | |
1961 | callbacks at each change via its ioctl. | |
1962 | ||
1963 | Thus, you need to be careful not to allocate the same buffers many | |
1964 | times, which will lead to memory leaks! Calling the helper function | |
1965 | above many times is OK. It will release the previous buffer | |
1966 | automatically when it was already allocated. | |
1967 | ||
1968 | Another note is that this callback is non-atomic (schedulable) as | |
1969 | default, i.e. when no ``nonatomic`` flag set. This is important, | |
1970 | because the ``trigger`` callback is atomic (non-schedulable). That is, | |
1971 | mutexes or any schedule-related functions are not available in | |
1972 | ``trigger`` callback. Please see the subsection Atomicity_ for | |
1973 | details. | |
1974 | ||
1975 | hw_free callback | |
1976 | ~~~~~~~~~~~~~~~~~ | |
1977 | ||
1978 | :: | |
1979 | ||
1980 | static int snd_xxx_hw_free(struct snd_pcm_substream *substream); | |
1981 | ||
1982 | This is called to release the resources allocated via | |
72b4bcbf | 1983 | ``hw_params``. |
7ddedebb TI |
1984 | |
1985 | This function is always called before the close callback is called. | |
1986 | Also, the callback may be called multiple times, too. Keep track | |
1987 | whether the resource was already released. | |
1988 | ||
72b4bcbf TI |
1989 | When you have set up the managed buffer allocation mode for the PCM |
1990 | substream, the allocated PCM buffer will be automatically released | |
1991 | after this callback gets called. Otherwise you'll have to release the | |
1992 | buffer manually. Typically, when the buffer was allocated from the | |
1993 | pre-allocated pool, you can use the standard API function | |
1994 | :c:func:`snd_pcm_lib_malloc_pages()` like: | |
1995 | ||
1996 | :: | |
1997 | ||
1998 | snd_pcm_lib_free_pages(substream); | |
1999 | ||
7ddedebb TI |
2000 | prepare callback |
2001 | ~~~~~~~~~~~~~~~~ | |
2002 | ||
2003 | :: | |
2004 | ||
2005 | static int snd_xxx_prepare(struct snd_pcm_substream *substream); | |
2006 | ||
2007 | This callback is called when the pcm is “prepared”. You can set the | |
2008 | format type, sample rate, etc. here. The difference from ``hw_params`` | |
2009 | is that the ``prepare`` callback will be called each time | |
2010 | :c:func:`snd_pcm_prepare()` is called, i.e. when recovering after | |
2011 | underruns, etc. | |
2012 | ||
2013 | Note that this callback is now non-atomic. You can use | |
2014 | schedule-related functions safely in this callback. | |
2015 | ||
2016 | In this and the following callbacks, you can refer to the values via | |
2017 | the runtime record, ``substream->runtime``. For example, to get the | |
2018 | current rate, format or channels, access to ``runtime->rate``, | |
2019 | ``runtime->format`` or ``runtime->channels``, respectively. The | |
2020 | physical address of the allocated buffer is set to | |
2021 | ``runtime->dma_area``. The buffer and period sizes are in | |
2022 | ``runtime->buffer_size`` and ``runtime->period_size``, respectively. | |
2023 | ||
2024 | Be careful that this callback will be called many times at each setup, | |
2025 | too. | |
2026 | ||
2027 | trigger callback | |
2028 | ~~~~~~~~~~~~~~~~ | |
2029 | ||
2030 | :: | |
2031 | ||
2032 | static int snd_xxx_trigger(struct snd_pcm_substream *substream, int cmd); | |
2033 | ||
2034 | This is called when the pcm is started, stopped or paused. | |
2035 | ||
2036 | Which action is specified in the second argument, | |
2037 | ``SNDRV_PCM_TRIGGER_XXX`` in ``<sound/pcm.h>``. At least, the ``START`` | |
2038 | and ``STOP`` commands must be defined in this callback. | |
2039 | ||
2040 | :: | |
2041 | ||
2042 | switch (cmd) { | |
2043 | case SNDRV_PCM_TRIGGER_START: | |
2044 | /* do something to start the PCM engine */ | |
2045 | break; | |
2046 | case SNDRV_PCM_TRIGGER_STOP: | |
2047 | /* do something to stop the PCM engine */ | |
2048 | break; | |
2049 | default: | |
2050 | return -EINVAL; | |
2051 | } | |
2052 | ||
2053 | When the pcm supports the pause operation (given in the info field of | |
2054 | the hardware table), the ``PAUSE_PUSH`` and ``PAUSE_RELEASE`` commands | |
2055 | must be handled here, too. The former is the command to pause the pcm, | |
2056 | and the latter to restart the pcm again. | |
2057 | ||
2058 | When the pcm supports the suspend/resume operation, regardless of full | |
2059 | or partial suspend/resume support, the ``SUSPEND`` and ``RESUME`` | |
2060 | commands must be handled, too. These commands are issued when the | |
2061 | power-management status is changed. Obviously, the ``SUSPEND`` and | |
2062 | ``RESUME`` commands suspend and resume the pcm substream, and usually, | |
2063 | they are identical to the ``STOP`` and ``START`` commands, respectively. | |
2064 | See the `Power Management`_ section for details. | |
2065 | ||
2066 | As mentioned, this callback is atomic as default unless ``nonatomic`` | |
2067 | flag set, and you cannot call functions which may sleep. The | |
2068 | ``trigger`` callback should be as minimal as possible, just really | |
2069 | triggering the DMA. The other stuff should be initialized | |
2070 | ``hw_params`` and ``prepare`` callbacks properly beforehand. | |
2071 | ||
94722e74 TI |
2072 | sync_stop callback |
2073 | ~~~~~~~~~~~~~~~~~~ | |
2074 | ||
2075 | :: | |
2076 | ||
2077 | static int snd_xxx_sync_stop(struct snd_pcm_substream *substream); | |
2078 | ||
2079 | This callback is optional, and NULL can be passed. It's called after | |
2080 | the PCM core stops the stream and changes the stream state | |
2081 | ``prepare``, ``hw_params`` or ``hw_free``. | |
2082 | Since the IRQ handler might be still pending, we need to wait until | |
2083 | the pending task finishes before moving to the next step; otherwise it | |
2084 | might lead to a crash due to resource conflicts or access to the freed | |
2085 | resources. A typical behavior is to call a synchronization function | |
2086 | like :c:func:`synchronize_irq()` here. | |
2087 | ||
2088 | For majority of drivers that need only a call of | |
2089 | :c:func:`synchronize_irq()`, there is a simpler setup, too. | |
2090 | While keeping NULL to ``sync_stop`` PCM callback, the driver can set | |
2091 | ``card->sync_irq`` field to store the valid interrupt number after | |
2092 | requesting an IRQ, instead. Then PCM core will look call | |
2093 | :c:func:`synchronize_irq()` with the given IRQ appropriately. | |
2094 | ||
2095 | If the IRQ handler is released at the card destructor, you don't need | |
2096 | to clear ``card->sync_irq``, as the card itself is being released. | |
2097 | So, usually you'll need to add just a single line for assigning | |
2098 | ``card->sync_irq`` in the driver code unless the driver re-acquires | |
2099 | the IRQ. When the driver frees and re-acquires the IRQ dynamically | |
2100 | (e.g. for suspend/resume), it needs to clear and re-set | |
2101 | ``card->sync_irq`` again appropriately. | |
2102 | ||
7ddedebb TI |
2103 | pointer callback |
2104 | ~~~~~~~~~~~~~~~~ | |
2105 | ||
2106 | :: | |
2107 | ||
2108 | static snd_pcm_uframes_t snd_xxx_pointer(struct snd_pcm_substream *substream) | |
2109 | ||
2110 | This callback is called when the PCM middle layer inquires the current | |
2111 | hardware position on the buffer. The position must be returned in | |
2112 | frames, ranging from 0 to ``buffer_size - 1``. | |
2113 | ||
2114 | This is called usually from the buffer-update routine in the pcm | |
2115 | middle layer, which is invoked when :c:func:`snd_pcm_period_elapsed()` | |
2116 | is called in the interrupt routine. Then the pcm middle layer updates | |
2117 | the position and calculates the available space, and wakes up the | |
2118 | sleeping poll threads, etc. | |
2119 | ||
2120 | This callback is also atomic as default. | |
2121 | ||
f7a47817 TI |
2122 | copy_user, copy_kernel and fill_silence ops |
2123 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
7ddedebb TI |
2124 | |
2125 | These callbacks are not mandatory, and can be omitted in most cases. | |
2126 | These callbacks are used when the hardware buffer cannot be in the | |
2127 | normal memory space. Some chips have their own buffer on the hardware | |
2128 | which is not mappable. In such a case, you have to transfer the data | |
2129 | manually from the memory buffer to the hardware buffer. Or, if the | |
2130 | buffer is non-contiguous on both physical and virtual memory spaces, | |
2131 | these callbacks must be defined, too. | |
2132 | ||
2133 | If these two callbacks are defined, copy and set-silence operations | |
2134 | are done by them. The detailed will be described in the later section | |
2135 | `Buffer and Memory Management`_. | |
2136 | ||
2137 | ack callback | |
2138 | ~~~~~~~~~~~~ | |
2139 | ||
2140 | This callback is also not mandatory. This callback is called when the | |
2141 | ``appl_ptr`` is updated in read or write operations. Some drivers like | |
2142 | emu10k1-fx and cs46xx need to track the current ``appl_ptr`` for the | |
2143 | internal buffer, and this callback is useful only for such a purpose. | |
2144 | ||
2145 | This callback is atomic as default. | |
2146 | ||
2147 | page callback | |
2148 | ~~~~~~~~~~~~~ | |
2149 | ||
abffd8d0 TI |
2150 | This callback is optional too. The mmap calls this callback to get the |
2151 | page fault address. | |
2152 | ||
2153 | Since the recent changes, you need no special callback any longer for | |
2154 | the standard SG-buffer or vmalloc-buffer. Hence this callback should | |
2155 | be rarely used. | |
7ddedebb | 2156 | |
f90afe79 TI |
2157 | mmap calllback |
2158 | ~~~~~~~~~~~~~~ | |
2159 | ||
2160 | This is another optional callback for controlling mmap behavior. | |
2161 | Once when defined, PCM core calls this callback when a page is | |
2162 | memory-mapped instead of dealing via the standard helper. | |
2163 | If you need special handling (due to some architecture or | |
2164 | device-specific issues), implement everything here as you like. | |
2165 | ||
2166 | ||
7ddedebb TI |
2167 | PCM Interrupt Handler |
2168 | --------------------- | |
2169 | ||
2170 | The rest of pcm stuff is the PCM interrupt handler. The role of PCM | |
2171 | interrupt handler in the sound driver is to update the buffer position | |
2172 | and to tell the PCM middle layer when the buffer position goes across | |
2173 | the prescribed period size. To inform this, call the | |
2174 | :c:func:`snd_pcm_period_elapsed()` function. | |
2175 | ||
2176 | There are several types of sound chips to generate the interrupts. | |
2177 | ||
2178 | Interrupts at the period (fragment) boundary | |
2179 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
2180 | ||
2181 | This is the most frequently found type: the hardware generates an | |
2182 | interrupt at each period boundary. In this case, you can call | |
2183 | :c:func:`snd_pcm_period_elapsed()` at each interrupt. | |
2184 | ||
2185 | :c:func:`snd_pcm_period_elapsed()` takes the substream pointer as | |
2186 | its argument. Thus, you need to keep the substream pointer accessible | |
2187 | from the chip instance. For example, define ``substream`` field in the | |
2188 | chip record to hold the current running substream pointer, and set the | |
2189 | pointer value at ``open`` callback (and reset at ``close`` callback). | |
2190 | ||
2191 | If you acquire a spinlock in the interrupt handler, and the lock is used | |
2192 | in other pcm callbacks, too, then you have to release the lock before | |
2193 | calling :c:func:`snd_pcm_period_elapsed()`, because | |
2194 | :c:func:`snd_pcm_period_elapsed()` calls other pcm callbacks | |
2195 | inside. | |
2196 | ||
2197 | Typical code would be like: | |
2198 | ||
2199 | :: | |
2200 | ||
2201 | ||
2202 | static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id) | |
2203 | { | |
2204 | struct mychip *chip = dev_id; | |
2205 | spin_lock(&chip->lock); | |
2206 | .... | |
2207 | if (pcm_irq_invoked(chip)) { | |
2208 | /* call updater, unlock before it */ | |
2209 | spin_unlock(&chip->lock); | |
2210 | snd_pcm_period_elapsed(chip->substream); | |
2211 | spin_lock(&chip->lock); | |
2212 | /* acknowledge the interrupt if necessary */ | |
2213 | } | |
2214 | .... | |
2215 | spin_unlock(&chip->lock); | |
2216 | return IRQ_HANDLED; | |
2217 | } | |
2218 | ||
2219 | ||
2220 | ||
2221 | High frequency timer interrupts | |
2222 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
2223 | ||
2224 | This happens when the hardware doesn't generate interrupts at the period | |
2225 | boundary but issues timer interrupts at a fixed timer rate (e.g. es1968 | |
2226 | or ymfpci drivers). In this case, you need to check the current hardware | |
2227 | position and accumulate the processed sample length at each interrupt. | |
2228 | When the accumulated size exceeds the period size, call | |
2229 | :c:func:`snd_pcm_period_elapsed()` and reset the accumulator. | |
2230 | ||
2231 | Typical code would be like the following. | |
2232 | ||
2233 | :: | |
2234 | ||
2235 | ||
2236 | static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id) | |
2237 | { | |
2238 | struct mychip *chip = dev_id; | |
2239 | spin_lock(&chip->lock); | |
2240 | .... | |
2241 | if (pcm_irq_invoked(chip)) { | |
2242 | unsigned int last_ptr, size; | |
2243 | /* get the current hardware pointer (in frames) */ | |
2244 | last_ptr = get_hw_ptr(chip); | |
2245 | /* calculate the processed frames since the | |
2246 | * last update | |
2247 | */ | |
2248 | if (last_ptr < chip->last_ptr) | |
2249 | size = runtime->buffer_size + last_ptr | |
2250 | - chip->last_ptr; | |
2251 | else | |
2252 | size = last_ptr - chip->last_ptr; | |
2253 | /* remember the last updated point */ | |
2254 | chip->last_ptr = last_ptr; | |
2255 | /* accumulate the size */ | |
2256 | chip->size += size; | |
2257 | /* over the period boundary? */ | |
2258 | if (chip->size >= runtime->period_size) { | |
2259 | /* reset the accumulator */ | |
2260 | chip->size %= runtime->period_size; | |
2261 | /* call updater */ | |
2262 | spin_unlock(&chip->lock); | |
2263 | snd_pcm_period_elapsed(substream); | |
2264 | spin_lock(&chip->lock); | |
2265 | } | |
2266 | /* acknowledge the interrupt if necessary */ | |
2267 | } | |
2268 | .... | |
2269 | spin_unlock(&chip->lock); | |
2270 | return IRQ_HANDLED; | |
2271 | } | |
2272 | ||
2273 | ||
2274 | ||
2275 | On calling :c:func:`snd_pcm_period_elapsed()` | |
2276 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
2277 | ||
2278 | In both cases, even if more than one period are elapsed, you don't have | |
2279 | to call :c:func:`snd_pcm_period_elapsed()` many times. Call only | |
2280 | once. And the pcm layer will check the current hardware pointer and | |
2281 | update to the latest status. | |
2282 | ||
2283 | Atomicity | |
2284 | --------- | |
2285 | ||
2286 | One of the most important (and thus difficult to debug) problems in | |
2287 | kernel programming are race conditions. In the Linux kernel, they are | |
2288 | usually avoided via spin-locks, mutexes or semaphores. In general, if a | |
2289 | race condition can happen in an interrupt handler, it has to be managed | |
2290 | atomically, and you have to use a spinlock to protect the critical | |
2291 | session. If the critical section is not in interrupt handler code and if | |
2292 | taking a relatively long time to execute is acceptable, you should use | |
2293 | mutexes or semaphores instead. | |
2294 | ||
2295 | As already seen, some pcm callbacks are atomic and some are not. For | |
2296 | example, the ``hw_params`` callback is non-atomic, while ``trigger`` | |
2297 | callback is atomic. This means, the latter is called already in a | |
2298 | spinlock held by the PCM middle layer. Please take this atomicity into | |
2299 | account when you choose a locking scheme in the callbacks. | |
2300 | ||
2301 | In the atomic callbacks, you cannot use functions which may call | |
2302 | :c:func:`schedule()` or go to :c:func:`sleep()`. Semaphores and | |
2303 | mutexes can sleep, and hence they cannot be used inside the atomic | |
2304 | callbacks (e.g. ``trigger`` callback). To implement some delay in such a | |
2305 | callback, please use :c:func:`udelay()` or :c:func:`mdelay()`. | |
2306 | ||
2307 | All three atomic callbacks (trigger, pointer, and ack) are called with | |
2308 | local interrupts disabled. | |
2309 | ||
2310 | The recent changes in PCM core code, however, allow all PCM operations | |
2311 | to be non-atomic. This assumes that the all caller sides are in | |
2312 | non-atomic contexts. For example, the function | |
2313 | :c:func:`snd_pcm_period_elapsed()` is called typically from the | |
2314 | interrupt handler. But, if you set up the driver to use a threaded | |
2315 | interrupt handler, this call can be in non-atomic context, too. In such | |
2316 | a case, you can set ``nonatomic`` filed of :c:type:`struct snd_pcm | |
2317 | <snd_pcm>` object after creating it. When this flag is set, mutex | |
2318 | and rwsem are used internally in the PCM core instead of spin and | |
2319 | rwlocks, so that you can call all PCM functions safely in a non-atomic | |
2320 | context. | |
2321 | ||
2322 | Constraints | |
2323 | ----------- | |
2324 | ||
2325 | If your chip supports unconventional sample rates, or only the limited | |
2326 | samples, you need to set a constraint for the condition. | |
2327 | ||
2328 | For example, in order to restrict the sample rates in the some supported | |
2329 | values, use :c:func:`snd_pcm_hw_constraint_list()`. You need to | |
2330 | call this function in the open callback. | |
2331 | ||
2332 | :: | |
2333 | ||
2334 | static unsigned int rates[] = | |
2335 | {4000, 10000, 22050, 44100}; | |
2336 | static struct snd_pcm_hw_constraint_list constraints_rates = { | |
2337 | .count = ARRAY_SIZE(rates), | |
2338 | .list = rates, | |
2339 | .mask = 0, | |
2340 | }; | |
2341 | ||
2342 | static int snd_mychip_pcm_open(struct snd_pcm_substream *substream) | |
2343 | { | |
2344 | int err; | |
2345 | .... | |
2346 | err = snd_pcm_hw_constraint_list(substream->runtime, 0, | |
2347 | SNDRV_PCM_HW_PARAM_RATE, | |
2348 | &constraints_rates); | |
2349 | if (err < 0) | |
2350 | return err; | |
2351 | .... | |
2352 | } | |
2353 | ||
2354 | ||
2355 | ||
2356 | There are many different constraints. Look at ``sound/pcm.h`` for a | |
2357 | complete list. You can even define your own constraint rules. For | |
2358 | example, let's suppose my_chip can manage a substream of 1 channel if | |
2359 | and only if the format is ``S16_LE``, otherwise it supports any format | |
2360 | specified in the :c:type:`struct snd_pcm_hardware | |
2361 | <snd_pcm_hardware>` structure (or in any other | |
2362 | constraint_list). You can build a rule like this: | |
2363 | ||
2364 | :: | |
2365 | ||
2366 | static int hw_rule_channels_by_format(struct snd_pcm_hw_params *params, | |
2367 | struct snd_pcm_hw_rule *rule) | |
2368 | { | |
2369 | struct snd_interval *c = hw_param_interval(params, | |
2370 | SNDRV_PCM_HW_PARAM_CHANNELS); | |
2371 | struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT); | |
2372 | struct snd_interval ch; | |
2373 | ||
2374 | snd_interval_any(&ch); | |
2375 | if (f->bits[0] == SNDRV_PCM_FMTBIT_S16_LE) { | |
2376 | ch.min = ch.max = 1; | |
2377 | ch.integer = 1; | |
2378 | return snd_interval_refine(c, &ch); | |
2379 | } | |
2380 | return 0; | |
2381 | } | |
2382 | ||
2383 | ||
2384 | Then you need to call this function to add your rule: | |
2385 | ||
2386 | :: | |
2387 | ||
2388 | snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS, | |
2389 | hw_rule_channels_by_format, NULL, | |
2390 | SNDRV_PCM_HW_PARAM_FORMAT, -1); | |
2391 | ||
2392 | The rule function is called when an application sets the PCM format, and | |
2393 | it refines the number of channels accordingly. But an application may | |
2394 | set the number of channels before setting the format. Thus you also need | |
2395 | to define the inverse rule: | |
2396 | ||
2397 | :: | |
2398 | ||
2399 | static int hw_rule_format_by_channels(struct snd_pcm_hw_params *params, | |
2400 | struct snd_pcm_hw_rule *rule) | |
2401 | { | |
2402 | struct snd_interval *c = hw_param_interval(params, | |
2403 | SNDRV_PCM_HW_PARAM_CHANNELS); | |
2404 | struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT); | |
2405 | struct snd_mask fmt; | |
2406 | ||
2407 | snd_mask_any(&fmt); /* Init the struct */ | |
2408 | if (c->min < 2) { | |
2409 | fmt.bits[0] &= SNDRV_PCM_FMTBIT_S16_LE; | |
2410 | return snd_mask_refine(f, &fmt); | |
2411 | } | |
2412 | return 0; | |
2413 | } | |
2414 | ||
2415 | ||
2416 | ... and in the open callback: | |
2417 | ||
2418 | :: | |
2419 | ||
2420 | snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT, | |
2421 | hw_rule_format_by_channels, NULL, | |
2422 | SNDRV_PCM_HW_PARAM_CHANNELS, -1); | |
2423 | ||
f90afe79 TI |
2424 | One typical usage of the hw constraints is to align the buffer size |
2425 | with the period size. As default, ALSA PCM core doesn't enforce the | |
2426 | buffer size to be aligned with the period size. For example, it'd be | |
2427 | possible to have a combination like 256 period bytes with 999 buffer | |
2428 | bytes. | |
2429 | ||
2430 | Many device chips, however, require the buffer to be a multiple of | |
2431 | periods. In such a case, call | |
2432 | :c:func:`snd_pcm_hw_constraint_integer()` for | |
2433 | ``SNDRV_PCM_HW_PARAM_PERIODS``. | |
2434 | ||
2435 | :: | |
2436 | ||
2437 | snd_pcm_hw_constraint_integer(substream->runtime, | |
2438 | SNDRV_PCM_HW_PARAM_PERIODS); | |
2439 | ||
2440 | This assures that the number of periods is integer, hence the buffer | |
2441 | size is aligned with the period size. | |
2442 | ||
2443 | The hw constraint is a very much powerful mechanism to define the | |
2444 | preferred PCM configuration, and there are relevant helpers. | |
7ddedebb TI |
2445 | I won't give more details here, rather I would like to say, “Luke, use |
2446 | the source.” | |
2447 | ||
2448 | Control Interface | |
2449 | ================= | |
2450 | ||
2451 | General | |
2452 | ------- | |
2453 | ||
2454 | The control interface is used widely for many switches, sliders, etc. | |
2455 | which are accessed from user-space. Its most important use is the mixer | |
2456 | interface. In other words, since ALSA 0.9.x, all the mixer stuff is | |
2457 | implemented on the control kernel API. | |
2458 | ||
2459 | ALSA has a well-defined AC97 control module. If your chip supports only | |
2460 | the AC97 and nothing else, you can skip this section. | |
2461 | ||
2462 | The control API is defined in ``<sound/control.h>``. Include this file | |
2463 | if you want to add your own controls. | |
2464 | ||
2465 | Definition of Controls | |
2466 | ---------------------- | |
2467 | ||
2468 | To create a new control, you need to define the following three | |
2469 | callbacks: ``info``, ``get`` and ``put``. Then, define a | |
2470 | :c:type:`struct snd_kcontrol_new <snd_kcontrol_new>` record, such as: | |
2471 | ||
2472 | :: | |
2473 | ||
2474 | ||
2475 | static struct snd_kcontrol_new my_control = { | |
2476 | .iface = SNDRV_CTL_ELEM_IFACE_MIXER, | |
2477 | .name = "PCM Playback Switch", | |
2478 | .index = 0, | |
2479 | .access = SNDRV_CTL_ELEM_ACCESS_READWRITE, | |
2480 | .private_value = 0xffff, | |
2481 | .info = my_control_info, | |
2482 | .get = my_control_get, | |
2483 | .put = my_control_put | |
2484 | }; | |
2485 | ||
2486 | ||
2487 | The ``iface`` field specifies the control type, | |
2488 | ``SNDRV_CTL_ELEM_IFACE_XXX``, which is usually ``MIXER``. Use ``CARD`` | |
2489 | for global controls that are not logically part of the mixer. If the | |
2490 | control is closely associated with some specific device on the sound | |
2491 | card, use ``HWDEP``, ``PCM``, ``RAWMIDI``, ``TIMER``, or ``SEQUENCER``, | |
2492 | and specify the device number with the ``device`` and ``subdevice`` | |
2493 | fields. | |
2494 | ||
2495 | The ``name`` is the name identifier string. Since ALSA 0.9.x, the | |
2496 | control name is very important, because its role is classified from | |
2497 | its name. There are pre-defined standard control names. The details | |
2498 | are described in the `Control Names`_ subsection. | |
2499 | ||
2500 | The ``index`` field holds the index number of this control. If there | |
2501 | are several different controls with the same name, they can be | |
2502 | distinguished by the index number. This is the case when several | |
2503 | codecs exist on the card. If the index is zero, you can omit the | |
2504 | definition above. | |
2505 | ||
2506 | The ``access`` field contains the access type of this control. Give | |
2507 | the combination of bit masks, ``SNDRV_CTL_ELEM_ACCESS_XXX``, | |
2508 | there. The details will be explained in the `Access Flags`_ | |
2509 | subsection. | |
2510 | ||
2511 | The ``private_value`` field contains an arbitrary long integer value | |
2512 | for this record. When using the generic ``info``, ``get`` and ``put`` | |
2513 | callbacks, you can pass a value through this field. If several small | |
2514 | numbers are necessary, you can combine them in bitwise. Or, it's | |
2515 | possible to give a pointer (casted to unsigned long) of some record to | |
2516 | this field, too. | |
2517 | ||
2518 | The ``tlv`` field can be used to provide metadata about the control; | |
2519 | see the `Metadata`_ subsection. | |
2520 | ||
2521 | The other three are `Control Callbacks`_. | |
2522 | ||
2523 | Control Names | |
2524 | ------------- | |
2525 | ||
2526 | There are some standards to define the control names. A control is | |
2527 | usually defined from the three parts as “SOURCE DIRECTION FUNCTION”. | |
2528 | ||
2529 | The first, ``SOURCE``, specifies the source of the control, and is a | |
2530 | string such as “Master”, “PCM”, “CD” and “Line”. There are many | |
2531 | pre-defined sources. | |
2532 | ||
2533 | The second, ``DIRECTION``, is one of the following strings according to | |
2534 | the direction of the control: “Playback”, “Capture”, “Bypass Playback” | |
2535 | and “Bypass Capture”. Or, it can be omitted, meaning both playback and | |
2536 | capture directions. | |
2537 | ||
2538 | The third, ``FUNCTION``, is one of the following strings according to | |
2539 | the function of the control: “Switch”, “Volume” and “Route”. | |
2540 | ||
2541 | The example of control names are, thus, “Master Capture Switch” or “PCM | |
2542 | Playback Volume”. | |
2543 | ||
2544 | There are some exceptions: | |
2545 | ||
2546 | Global capture and playback | |
2547 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
2548 | ||
2549 | “Capture Source”, “Capture Switch” and “Capture Volume” are used for the | |
2550 | global capture (input) source, switch and volume. Similarly, “Playback | |
2551 | Switch” and “Playback Volume” are used for the global output gain switch | |
2552 | and volume. | |
2553 | ||
2554 | Tone-controls | |
2555 | ~~~~~~~~~~~~~ | |
2556 | ||
2557 | tone-control switch and volumes are specified like “Tone Control - XXX”, | |
2558 | e.g. “Tone Control - Switch”, “Tone Control - Bass”, “Tone Control - | |
2559 | Center”. | |
2560 | ||
2561 | 3D controls | |
2562 | ~~~~~~~~~~~ | |
2563 | ||
2564 | 3D-control switches and volumes are specified like “3D Control - XXX”, | |
2565 | e.g. “3D Control - Switch”, “3D Control - Center”, “3D Control - Space”. | |
2566 | ||
2567 | Mic boost | |
2568 | ~~~~~~~~~ | |
2569 | ||
2570 | Mic-boost switch is set as “Mic Boost” or “Mic Boost (6dB)”. | |
2571 | ||
2572 | More precise information can be found in | |
f495ae3c | 2573 | ``Documentation/sound/designs/control-names.rst``. |
7ddedebb TI |
2574 | |
2575 | Access Flags | |
2576 | ------------ | |
2577 | ||
2578 | The access flag is the bitmask which specifies the access type of the | |
2579 | given control. The default access type is | |
2580 | ``SNDRV_CTL_ELEM_ACCESS_READWRITE``, which means both read and write are | |
2581 | allowed to this control. When the access flag is omitted (i.e. = 0), it | |
2582 | is considered as ``READWRITE`` access as default. | |
2583 | ||
2584 | When the control is read-only, pass ``SNDRV_CTL_ELEM_ACCESS_READ`` | |
2585 | instead. In this case, you don't have to define the ``put`` callback. | |
2586 | Similarly, when the control is write-only (although it's a rare case), | |
2587 | you can use the ``WRITE`` flag instead, and you don't need the ``get`` | |
2588 | callback. | |
2589 | ||
2590 | If the control value changes frequently (e.g. the VU meter), | |
2591 | ``VOLATILE`` flag should be given. This means that the control may be | |
2592 | changed without `Change notification`_. Applications should poll such | |
2593 | a control constantly. | |
2594 | ||
2595 | When the control is inactive, set the ``INACTIVE`` flag, too. There are | |
2596 | ``LOCK`` and ``OWNER`` flags to change the write permissions. | |
2597 | ||
2598 | Control Callbacks | |
2599 | ----------------- | |
2600 | ||
2601 | info callback | |
2602 | ~~~~~~~~~~~~~ | |
2603 | ||
2604 | The ``info`` callback is used to get detailed information on this | |
2605 | control. This must store the values of the given :c:type:`struct | |
2606 | snd_ctl_elem_info <snd_ctl_elem_info>` object. For example, | |
2607 | for a boolean control with a single element: | |
2608 | ||
2609 | :: | |
2610 | ||
2611 | ||
2612 | static int snd_myctl_mono_info(struct snd_kcontrol *kcontrol, | |
2613 | struct snd_ctl_elem_info *uinfo) | |
2614 | { | |
2615 | uinfo->type = SNDRV_CTL_ELEM_TYPE_BOOLEAN; | |
2616 | uinfo->count = 1; | |
2617 | uinfo->value.integer.min = 0; | |
2618 | uinfo->value.integer.max = 1; | |
2619 | return 0; | |
2620 | } | |
2621 | ||
2622 | ||
2623 | ||
2624 | The ``type`` field specifies the type of the control. There are | |
2625 | ``BOOLEAN``, ``INTEGER``, ``ENUMERATED``, ``BYTES``, ``IEC958`` and | |
2626 | ``INTEGER64``. The ``count`` field specifies the number of elements in | |
2627 | this control. For example, a stereo volume would have count = 2. The | |
2628 | ``value`` field is a union, and the values stored are depending on the | |
2629 | type. The boolean and integer types are identical. | |
2630 | ||
2631 | The enumerated type is a bit different from others. You'll need to set | |
2632 | the string for the currently given item index. | |
2633 | ||
2634 | :: | |
2635 | ||
2636 | static int snd_myctl_enum_info(struct snd_kcontrol *kcontrol, | |
2637 | struct snd_ctl_elem_info *uinfo) | |
2638 | { | |
2639 | static char *texts[4] = { | |
2640 | "First", "Second", "Third", "Fourth" | |
2641 | }; | |
2642 | uinfo->type = SNDRV_CTL_ELEM_TYPE_ENUMERATED; | |
2643 | uinfo->count = 1; | |
2644 | uinfo->value.enumerated.items = 4; | |
2645 | if (uinfo->value.enumerated.item > 3) | |
2646 | uinfo->value.enumerated.item = 3; | |
2647 | strcpy(uinfo->value.enumerated.name, | |
2648 | texts[uinfo->value.enumerated.item]); | |
2649 | return 0; | |
2650 | } | |
2651 | ||
2652 | The above callback can be simplified with a helper function, | |
2653 | :c:func:`snd_ctl_enum_info()`. The final code looks like below. | |
2654 | (You can pass ``ARRAY_SIZE(texts)`` instead of 4 in the third argument; | |
2655 | it's a matter of taste.) | |
2656 | ||
2657 | :: | |
2658 | ||
2659 | static int snd_myctl_enum_info(struct snd_kcontrol *kcontrol, | |
2660 | struct snd_ctl_elem_info *uinfo) | |
2661 | { | |
2662 | static char *texts[4] = { | |
2663 | "First", "Second", "Third", "Fourth" | |
2664 | }; | |
2665 | return snd_ctl_enum_info(uinfo, 1, 4, texts); | |
2666 | } | |
2667 | ||
2668 | ||
2669 | Some common info callbacks are available for your convenience: | |
2670 | :c:func:`snd_ctl_boolean_mono_info()` and | |
2671 | :c:func:`snd_ctl_boolean_stereo_info()`. Obviously, the former | |
2672 | is an info callback for a mono channel boolean item, just like | |
2673 | :c:func:`snd_myctl_mono_info()` above, and the latter is for a | |
2674 | stereo channel boolean item. | |
2675 | ||
2676 | get callback | |
2677 | ~~~~~~~~~~~~ | |
2678 | ||
2679 | This callback is used to read the current value of the control and to | |
2680 | return to user-space. | |
2681 | ||
2682 | For example, | |
2683 | ||
2684 | :: | |
2685 | ||
2686 | ||
2687 | static int snd_myctl_get(struct snd_kcontrol *kcontrol, | |
2688 | struct snd_ctl_elem_value *ucontrol) | |
2689 | { | |
2690 | struct mychip *chip = snd_kcontrol_chip(kcontrol); | |
2691 | ucontrol->value.integer.value[0] = get_some_value(chip); | |
2692 | return 0; | |
2693 | } | |
2694 | ||
2695 | ||
2696 | ||
2697 | The ``value`` field depends on the type of control as well as on the | |
2698 | info callback. For example, the sb driver uses this field to store the | |
2699 | register offset, the bit-shift and the bit-mask. The ``private_value`` | |
2700 | field is set as follows: | |
2701 | ||
2702 | :: | |
2703 | ||
2704 | .private_value = reg | (shift << 16) | (mask << 24) | |
2705 | ||
2706 | and is retrieved in callbacks like | |
2707 | ||
2708 | :: | |
2709 | ||
2710 | static int snd_sbmixer_get_single(struct snd_kcontrol *kcontrol, | |
2711 | struct snd_ctl_elem_value *ucontrol) | |
2712 | { | |
2713 | int reg = kcontrol->private_value & 0xff; | |
2714 | int shift = (kcontrol->private_value >> 16) & 0xff; | |
2715 | int mask = (kcontrol->private_value >> 24) & 0xff; | |
2716 | .... | |
2717 | } | |
2718 | ||
2719 | In the ``get`` callback, you have to fill all the elements if the | |
2720 | control has more than one elements, i.e. ``count > 1``. In the example | |
2721 | above, we filled only one element (``value.integer.value[0]``) since | |
2722 | it's assumed as ``count = 1``. | |
2723 | ||
2724 | put callback | |
2725 | ~~~~~~~~~~~~ | |
2726 | ||
2727 | This callback is used to write a value from user-space. | |
2728 | ||
2729 | For example, | |
2730 | ||
2731 | :: | |
2732 | ||
2733 | ||
2734 | static int snd_myctl_put(struct snd_kcontrol *kcontrol, | |
2735 | struct snd_ctl_elem_value *ucontrol) | |
2736 | { | |
2737 | struct mychip *chip = snd_kcontrol_chip(kcontrol); | |
2738 | int changed = 0; | |
2739 | if (chip->current_value != | |
2740 | ucontrol->value.integer.value[0]) { | |
2741 | change_current_value(chip, | |
2742 | ucontrol->value.integer.value[0]); | |
2743 | changed = 1; | |
2744 | } | |
2745 | return changed; | |
2746 | } | |
2747 | ||
2748 | ||
2749 | ||
2750 | As seen above, you have to return 1 if the value is changed. If the | |
2751 | value is not changed, return 0 instead. If any fatal error happens, | |
2752 | return a negative error code as usual. | |
2753 | ||
2754 | As in the ``get`` callback, when the control has more than one | |
2755 | elements, all elements must be evaluated in this callback, too. | |
2756 | ||
2757 | Callbacks are not atomic | |
2758 | ~~~~~~~~~~~~~~~~~~~~~~~~ | |
2759 | ||
2760 | All these three callbacks are basically not atomic. | |
2761 | ||
2762 | Control Constructor | |
2763 | ------------------- | |
2764 | ||
2765 | When everything is ready, finally we can create a new control. To create | |
2766 | a control, there are two functions to be called, | |
2767 | :c:func:`snd_ctl_new1()` and :c:func:`snd_ctl_add()`. | |
2768 | ||
2769 | In the simplest way, you can do like this: | |
2770 | ||
2771 | :: | |
2772 | ||
2773 | err = snd_ctl_add(card, snd_ctl_new1(&my_control, chip)); | |
2774 | if (err < 0) | |
2775 | return err; | |
2776 | ||
2777 | where ``my_control`` is the :c:type:`struct snd_kcontrol_new | |
2778 | <snd_kcontrol_new>` object defined above, and chip is the object | |
2779 | pointer to be passed to kcontrol->private_data which can be referred | |
2780 | to in callbacks. | |
2781 | ||
2782 | :c:func:`snd_ctl_new1()` allocates a new :c:type:`struct | |
2783 | snd_kcontrol <snd_kcontrol>` instance, and | |
2784 | :c:func:`snd_ctl_add()` assigns the given control component to the | |
2785 | card. | |
2786 | ||
2787 | Change Notification | |
2788 | ------------------- | |
2789 | ||
2790 | If you need to change and update a control in the interrupt routine, you | |
2791 | can call :c:func:`snd_ctl_notify()`. For example, | |
2792 | ||
2793 | :: | |
2794 | ||
2795 | snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_VALUE, id_pointer); | |
2796 | ||
2797 | This function takes the card pointer, the event-mask, and the control id | |
2798 | pointer for the notification. The event-mask specifies the types of | |
2799 | notification, for example, in the above example, the change of control | |
2800 | values is notified. The id pointer is the pointer of :c:type:`struct | |
2801 | snd_ctl_elem_id <snd_ctl_elem_id>` to be notified. You can | |
2802 | find some examples in ``es1938.c`` or ``es1968.c`` for hardware volume | |
2803 | interrupts. | |
2804 | ||
2805 | Metadata | |
2806 | -------- | |
2807 | ||
2808 | To provide information about the dB values of a mixer control, use on of | |
2809 | the ``DECLARE_TLV_xxx`` macros from ``<sound/tlv.h>`` to define a | |
2810 | variable containing this information, set the ``tlv.p`` field to point to | |
2811 | this variable, and include the ``SNDRV_CTL_ELEM_ACCESS_TLV_READ`` flag | |
2812 | in the ``access`` field; like this: | |
2813 | ||
2814 | :: | |
2815 | ||
2816 | static DECLARE_TLV_DB_SCALE(db_scale_my_control, -4050, 150, 0); | |
2817 | ||
2818 | static struct snd_kcontrol_new my_control = { | |
2819 | ... | |
2820 | .access = SNDRV_CTL_ELEM_ACCESS_READWRITE | | |
2821 | SNDRV_CTL_ELEM_ACCESS_TLV_READ, | |
2822 | ... | |
2823 | .tlv.p = db_scale_my_control, | |
2824 | }; | |
2825 | ||
2826 | ||
2827 | The :c:func:`DECLARE_TLV_DB_SCALE()` macro defines information | |
2828 | about a mixer control where each step in the control's value changes the | |
2829 | dB value by a constant dB amount. The first parameter is the name of the | |
2830 | variable to be defined. The second parameter is the minimum value, in | |
2831 | units of 0.01 dB. The third parameter is the step size, in units of 0.01 | |
2832 | dB. Set the fourth parameter to 1 if the minimum value actually mutes | |
2833 | the control. | |
2834 | ||
2835 | The :c:func:`DECLARE_TLV_DB_LINEAR()` macro defines information | |
2836 | about a mixer control where the control's value affects the output | |
2837 | linearly. The first parameter is the name of the variable to be defined. | |
2838 | The second parameter is the minimum value, in units of 0.01 dB. The | |
2839 | third parameter is the maximum value, in units of 0.01 dB. If the | |
2840 | minimum value mutes the control, set the second parameter to | |
2841 | ``TLV_DB_GAIN_MUTE``. | |
2842 | ||
2843 | API for AC97 Codec | |
2844 | ================== | |
2845 | ||
2846 | General | |
2847 | ------- | |
2848 | ||
2849 | The ALSA AC97 codec layer is a well-defined one, and you don't have to | |
2850 | write much code to control it. Only low-level control routines are | |
2851 | necessary. The AC97 codec API is defined in ``<sound/ac97_codec.h>``. | |
2852 | ||
2853 | Full Code Example | |
2854 | ----------------- | |
2855 | ||
2856 | :: | |
2857 | ||
2858 | struct mychip { | |
2859 | .... | |
2860 | struct snd_ac97 *ac97; | |
2861 | .... | |
2862 | }; | |
2863 | ||
2864 | static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97, | |
2865 | unsigned short reg) | |
2866 | { | |
2867 | struct mychip *chip = ac97->private_data; | |
2868 | .... | |
2869 | /* read a register value here from the codec */ | |
2870 | return the_register_value; | |
2871 | } | |
2872 | ||
2873 | static void snd_mychip_ac97_write(struct snd_ac97 *ac97, | |
2874 | unsigned short reg, unsigned short val) | |
2875 | { | |
2876 | struct mychip *chip = ac97->private_data; | |
2877 | .... | |
2878 | /* write the given register value to the codec */ | |
2879 | } | |
2880 | ||
2881 | static int snd_mychip_ac97(struct mychip *chip) | |
2882 | { | |
2883 | struct snd_ac97_bus *bus; | |
2884 | struct snd_ac97_template ac97; | |
2885 | int err; | |
2886 | static struct snd_ac97_bus_ops ops = { | |
2887 | .write = snd_mychip_ac97_write, | |
2888 | .read = snd_mychip_ac97_read, | |
2889 | }; | |
2890 | ||
2891 | err = snd_ac97_bus(chip->card, 0, &ops, NULL, &bus); | |
2892 | if (err < 0) | |
2893 | return err; | |
2894 | memset(&ac97, 0, sizeof(ac97)); | |
2895 | ac97.private_data = chip; | |
2896 | return snd_ac97_mixer(bus, &ac97, &chip->ac97); | |
2897 | } | |
2898 | ||
2899 | ||
2900 | AC97 Constructor | |
2901 | ---------------- | |
2902 | ||
2903 | To create an ac97 instance, first call :c:func:`snd_ac97_bus()` | |
2904 | with an ``ac97_bus_ops_t`` record with callback functions. | |
2905 | ||
2906 | :: | |
2907 | ||
2908 | struct snd_ac97_bus *bus; | |
2909 | static struct snd_ac97_bus_ops ops = { | |
2910 | .write = snd_mychip_ac97_write, | |
2911 | .read = snd_mychip_ac97_read, | |
2912 | }; | |
2913 | ||
2914 | snd_ac97_bus(card, 0, &ops, NULL, &pbus); | |
2915 | ||
2916 | The bus record is shared among all belonging ac97 instances. | |
2917 | ||
2918 | And then call :c:func:`snd_ac97_mixer()` with an :c:type:`struct | |
2919 | snd_ac97_template <snd_ac97_template>` record together with | |
2920 | the bus pointer created above. | |
2921 | ||
2922 | :: | |
2923 | ||
2924 | struct snd_ac97_template ac97; | |
2925 | int err; | |
2926 | ||
2927 | memset(&ac97, 0, sizeof(ac97)); | |
2928 | ac97.private_data = chip; | |
2929 | snd_ac97_mixer(bus, &ac97, &chip->ac97); | |
2930 | ||
2931 | where chip->ac97 is a pointer to a newly created ``ac97_t`` | |
2932 | instance. In this case, the chip pointer is set as the private data, | |
2933 | so that the read/write callback functions can refer to this chip | |
2934 | instance. This instance is not necessarily stored in the chip | |
2935 | record. If you need to change the register values from the driver, or | |
2936 | need the suspend/resume of ac97 codecs, keep this pointer to pass to | |
2937 | the corresponding functions. | |
2938 | ||
2939 | AC97 Callbacks | |
2940 | -------------- | |
2941 | ||
2942 | The standard callbacks are ``read`` and ``write``. Obviously they | |
2943 | correspond to the functions for read and write accesses to the | |
2944 | hardware low-level codes. | |
2945 | ||
2946 | The ``read`` callback returns the register value specified in the | |
2947 | argument. | |
2948 | ||
2949 | :: | |
2950 | ||
2951 | static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97, | |
2952 | unsigned short reg) | |
2953 | { | |
2954 | struct mychip *chip = ac97->private_data; | |
2955 | .... | |
2956 | return the_register_value; | |
2957 | } | |
2958 | ||
2959 | Here, the chip can be cast from ``ac97->private_data``. | |
2960 | ||
2961 | Meanwhile, the ``write`` callback is used to set the register | |
2962 | value | |
2963 | ||
2964 | :: | |
2965 | ||
2966 | static void snd_mychip_ac97_write(struct snd_ac97 *ac97, | |
2967 | unsigned short reg, unsigned short val) | |
2968 | ||
2969 | ||
2970 | These callbacks are non-atomic like the control API callbacks. | |
2971 | ||
2972 | There are also other callbacks: ``reset``, ``wait`` and ``init``. | |
2973 | ||
2974 | The ``reset`` callback is used to reset the codec. If the chip | |
2975 | requires a special kind of reset, you can define this callback. | |
2976 | ||
2977 | The ``wait`` callback is used to add some waiting time in the standard | |
2978 | initialization of the codec. If the chip requires the extra waiting | |
2979 | time, define this callback. | |
2980 | ||
2981 | The ``init`` callback is used for additional initialization of the | |
2982 | codec. | |
2983 | ||
2984 | Updating Registers in The Driver | |
2985 | -------------------------------- | |
2986 | ||
2987 | If you need to access to the codec from the driver, you can call the | |
2988 | following functions: :c:func:`snd_ac97_write()`, | |
2989 | :c:func:`snd_ac97_read()`, :c:func:`snd_ac97_update()` and | |
2990 | :c:func:`snd_ac97_update_bits()`. | |
2991 | ||
2992 | Both :c:func:`snd_ac97_write()` and | |
2993 | :c:func:`snd_ac97_update()` functions are used to set a value to | |
2994 | the given register (``AC97_XXX``). The difference between them is that | |
2995 | :c:func:`snd_ac97_update()` doesn't write a value if the given | |
2996 | value has been already set, while :c:func:`snd_ac97_write()` | |
2997 | always rewrites the value. | |
2998 | ||
2999 | :: | |
3000 | ||
3001 | snd_ac97_write(ac97, AC97_MASTER, 0x8080); | |
3002 | snd_ac97_update(ac97, AC97_MASTER, 0x8080); | |
3003 | ||
3004 | :c:func:`snd_ac97_read()` is used to read the value of the given | |
3005 | register. For example, | |
3006 | ||
3007 | :: | |
3008 | ||
3009 | value = snd_ac97_read(ac97, AC97_MASTER); | |
3010 | ||
3011 | :c:func:`snd_ac97_update_bits()` is used to update some bits in | |
3012 | the given register. | |
3013 | ||
3014 | :: | |
3015 | ||
3016 | snd_ac97_update_bits(ac97, reg, mask, value); | |
3017 | ||
3018 | Also, there is a function to change the sample rate (of a given register | |
3019 | such as ``AC97_PCM_FRONT_DAC_RATE``) when VRA or DRA is supported by the | |
3020 | codec: :c:func:`snd_ac97_set_rate()`. | |
3021 | ||
3022 | :: | |
3023 | ||
3024 | snd_ac97_set_rate(ac97, AC97_PCM_FRONT_DAC_RATE, 44100); | |
3025 | ||
3026 | ||
3027 | The following registers are available to set the rate: | |
3028 | ``AC97_PCM_MIC_ADC_RATE``, ``AC97_PCM_FRONT_DAC_RATE``, | |
3029 | ``AC97_PCM_LR_ADC_RATE``, ``AC97_SPDIF``. When ``AC97_SPDIF`` is | |
3030 | specified, the register is not really changed but the corresponding | |
3031 | IEC958 status bits will be updated. | |
3032 | ||
3033 | Clock Adjustment | |
3034 | ---------------- | |
3035 | ||
3036 | In some chips, the clock of the codec isn't 48000 but using a PCI clock | |
3037 | (to save a quartz!). In this case, change the field ``bus->clock`` to | |
3038 | the corresponding value. For example, intel8x0 and es1968 drivers have | |
3039 | their own function to read from the clock. | |
3040 | ||
3041 | Proc Files | |
3042 | ---------- | |
3043 | ||
3044 | The ALSA AC97 interface will create a proc file such as | |
3045 | ``/proc/asound/card0/codec97#0/ac97#0-0`` and ``ac97#0-0+regs``. You | |
3046 | can refer to these files to see the current status and registers of | |
3047 | the codec. | |
3048 | ||
3049 | Multiple Codecs | |
3050 | --------------- | |
3051 | ||
3052 | When there are several codecs on the same card, you need to call | |
3053 | :c:func:`snd_ac97_mixer()` multiple times with ``ac97.num=1`` or | |
3054 | greater. The ``num`` field specifies the codec number. | |
3055 | ||
3056 | If you set up multiple codecs, you either need to write different | |
3057 | callbacks for each codec or check ``ac97->num`` in the callback | |
3058 | routines. | |
3059 | ||
3060 | MIDI (MPU401-UART) Interface | |
3061 | ============================ | |
3062 | ||
3063 | General | |
3064 | ------- | |
3065 | ||
3066 | Many soundcards have built-in MIDI (MPU401-UART) interfaces. When the | |
3067 | soundcard supports the standard MPU401-UART interface, most likely you | |
3068 | can use the ALSA MPU401-UART API. The MPU401-UART API is defined in | |
3069 | ``<sound/mpu401.h>``. | |
3070 | ||
3071 | Some soundchips have a similar but slightly different implementation of | |
3072 | mpu401 stuff. For example, emu10k1 has its own mpu401 routines. | |
3073 | ||
3074 | MIDI Constructor | |
3075 | ---------------- | |
3076 | ||
3077 | To create a rawmidi object, call :c:func:`snd_mpu401_uart_new()`. | |
3078 | ||
3079 | :: | |
3080 | ||
3081 | struct snd_rawmidi *rmidi; | |
3082 | snd_mpu401_uart_new(card, 0, MPU401_HW_MPU401, port, info_flags, | |
3083 | irq, &rmidi); | |
3084 | ||
3085 | ||
3086 | The first argument is the card pointer, and the second is the index of | |
3087 | this component. You can create up to 8 rawmidi devices. | |
3088 | ||
3089 | The third argument is the type of the hardware, ``MPU401_HW_XXX``. If | |
3090 | it's not a special one, you can use ``MPU401_HW_MPU401``. | |
3091 | ||
3092 | The 4th argument is the I/O port address. Many backward-compatible | |
3093 | MPU401 have an I/O port such as 0x330. Or, it might be a part of its own | |
3094 | PCI I/O region. It depends on the chip design. | |
3095 | ||
3096 | The 5th argument is a bitflag for additional information. When the I/O | |
3097 | port address above is part of the PCI I/O region, the MPU401 I/O port | |
3098 | might have been already allocated (reserved) by the driver itself. In | |
3099 | such a case, pass a bit flag ``MPU401_INFO_INTEGRATED``, and the | |
3100 | mpu401-uart layer will allocate the I/O ports by itself. | |
3101 | ||
3102 | When the controller supports only the input or output MIDI stream, pass | |
3103 | the ``MPU401_INFO_INPUT`` or ``MPU401_INFO_OUTPUT`` bitflag, | |
3104 | respectively. Then the rawmidi instance is created as a single stream. | |
3105 | ||
3106 | ``MPU401_INFO_MMIO`` bitflag is used to change the access method to MMIO | |
3107 | (via readb and writeb) instead of iob and outb. In this case, you have | |
3108 | to pass the iomapped address to :c:func:`snd_mpu401_uart_new()`. | |
3109 | ||
3110 | When ``MPU401_INFO_TX_IRQ`` is set, the output stream isn't checked in | |
3111 | the default interrupt handler. The driver needs to call | |
3112 | :c:func:`snd_mpu401_uart_interrupt_tx()` by itself to start | |
3113 | processing the output stream in the irq handler. | |
3114 | ||
3115 | If the MPU-401 interface shares its interrupt with the other logical | |
3116 | devices on the card, set ``MPU401_INFO_IRQ_HOOK`` (see | |
3117 | `below <#MIDI-Interrupt-Handler>`__). | |
3118 | ||
3119 | Usually, the port address corresponds to the command port and port + 1 | |
3120 | corresponds to the data port. If not, you may change the ``cport`` | |
3121 | field of :c:type:`struct snd_mpu401 <snd_mpu401>` manually afterward. | |
3122 | However, :c:type:`struct snd_mpu401 <snd_mpu401>` pointer is | |
3123 | not returned explicitly by :c:func:`snd_mpu401_uart_new()`. You | |
3124 | need to cast ``rmidi->private_data`` to :c:type:`struct snd_mpu401 | |
3125 | <snd_mpu401>` explicitly, | |
3126 | ||
3127 | :: | |
3128 | ||
3129 | struct snd_mpu401 *mpu; | |
3130 | mpu = rmidi->private_data; | |
3131 | ||
3132 | and reset the ``cport`` as you like: | |
3133 | ||
3134 | :: | |
3135 | ||
3136 | mpu->cport = my_own_control_port; | |
3137 | ||
3138 | The 6th argument specifies the ISA irq number that will be allocated. If | |
3139 | no interrupt is to be allocated (because your code is already allocating | |
3140 | a shared interrupt, or because the device does not use interrupts), pass | |
3141 | -1 instead. For a MPU-401 device without an interrupt, a polling timer | |
3142 | will be used instead. | |
3143 | ||
3144 | MIDI Interrupt Handler | |
3145 | ---------------------- | |
3146 | ||
3147 | When the interrupt is allocated in | |
3148 | :c:func:`snd_mpu401_uart_new()`, an exclusive ISA interrupt | |
3149 | handler is automatically used, hence you don't have anything else to do | |
3150 | than creating the mpu401 stuff. Otherwise, you have to set | |
3151 | ``MPU401_INFO_IRQ_HOOK``, and call | |
3152 | :c:func:`snd_mpu401_uart_interrupt()` explicitly from your own | |
3153 | interrupt handler when it has determined that a UART interrupt has | |
3154 | occurred. | |
3155 | ||
3156 | In this case, you need to pass the private_data of the returned rawmidi | |
3157 | object from :c:func:`snd_mpu401_uart_new()` as the second | |
3158 | argument of :c:func:`snd_mpu401_uart_interrupt()`. | |
3159 | ||
3160 | :: | |
3161 | ||
3162 | snd_mpu401_uart_interrupt(irq, rmidi->private_data, regs); | |
3163 | ||
3164 | ||
3165 | RawMIDI Interface | |
3166 | ================= | |
3167 | ||
3168 | Overview | |
3169 | -------- | |
3170 | ||
3171 | The raw MIDI interface is used for hardware MIDI ports that can be | |
3172 | accessed as a byte stream. It is not used for synthesizer chips that do | |
3173 | not directly understand MIDI. | |
3174 | ||
3175 | ALSA handles file and buffer management. All you have to do is to write | |
3176 | some code to move data between the buffer and the hardware. | |
3177 | ||
3178 | The rawmidi API is defined in ``<sound/rawmidi.h>``. | |
3179 | ||
3180 | RawMIDI Constructor | |
3181 | ------------------- | |
3182 | ||
3183 | To create a rawmidi device, call the :c:func:`snd_rawmidi_new()` | |
3184 | function: | |
3185 | ||
3186 | :: | |
3187 | ||
3188 | struct snd_rawmidi *rmidi; | |
3189 | err = snd_rawmidi_new(chip->card, "MyMIDI", 0, outs, ins, &rmidi); | |
3190 | if (err < 0) | |
3191 | return err; | |
3192 | rmidi->private_data = chip; | |
3193 | strcpy(rmidi->name, "My MIDI"); | |
3194 | rmidi->info_flags = SNDRV_RAWMIDI_INFO_OUTPUT | | |
3195 | SNDRV_RAWMIDI_INFO_INPUT | | |
3196 | SNDRV_RAWMIDI_INFO_DUPLEX; | |
3197 | ||
3198 | The first argument is the card pointer, the second argument is the ID | |
3199 | string. | |
3200 | ||
3201 | The third argument is the index of this component. You can create up to | |
3202 | 8 rawmidi devices. | |
3203 | ||
3204 | The fourth and fifth arguments are the number of output and input | |
3205 | substreams, respectively, of this device (a substream is the equivalent | |
3206 | of a MIDI port). | |
3207 | ||
3208 | Set the ``info_flags`` field to specify the capabilities of the | |
3209 | device. Set ``SNDRV_RAWMIDI_INFO_OUTPUT`` if there is at least one | |
3210 | output port, ``SNDRV_RAWMIDI_INFO_INPUT`` if there is at least one | |
3211 | input port, and ``SNDRV_RAWMIDI_INFO_DUPLEX`` if the device can handle | |
3212 | output and input at the same time. | |
3213 | ||
3214 | After the rawmidi device is created, you need to set the operators | |
3215 | (callbacks) for each substream. There are helper functions to set the | |
3216 | operators for all the substreams of a device: | |
3217 | ||
3218 | :: | |
3219 | ||
3220 | snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_OUTPUT, &snd_mymidi_output_ops); | |
3221 | snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_INPUT, &snd_mymidi_input_ops); | |
3222 | ||
3223 | The operators are usually defined like this: | |
3224 | ||
3225 | :: | |
3226 | ||
3227 | static struct snd_rawmidi_ops snd_mymidi_output_ops = { | |
3228 | .open = snd_mymidi_output_open, | |
3229 | .close = snd_mymidi_output_close, | |
3230 | .trigger = snd_mymidi_output_trigger, | |
3231 | }; | |
3232 | ||
3233 | These callbacks are explained in the `RawMIDI Callbacks`_ section. | |
3234 | ||
3235 | If there are more than one substream, you should give a unique name to | |
3236 | each of them: | |
3237 | ||
3238 | :: | |
3239 | ||
3240 | struct snd_rawmidi_substream *substream; | |
3241 | list_for_each_entry(substream, | |
3242 | &rmidi->streams[SNDRV_RAWMIDI_STREAM_OUTPUT].substreams, | |
3243 | list { | |
3244 | sprintf(substream->name, "My MIDI Port %d", substream->number + 1); | |
3245 | } | |
3246 | /* same for SNDRV_RAWMIDI_STREAM_INPUT */ | |
3247 | ||
3248 | RawMIDI Callbacks | |
3249 | ----------------- | |
3250 | ||
3251 | In all the callbacks, the private data that you've set for the rawmidi | |
3252 | device can be accessed as ``substream->rmidi->private_data``. | |
3253 | ||
3254 | If there is more than one port, your callbacks can determine the port | |
3255 | index from the struct snd_rawmidi_substream data passed to each | |
3256 | callback: | |
3257 | ||
3258 | :: | |
3259 | ||
3260 | struct snd_rawmidi_substream *substream; | |
3261 | int index = substream->number; | |
3262 | ||
3263 | RawMIDI open callback | |
3264 | ~~~~~~~~~~~~~~~~~~~~~ | |
3265 | ||
3266 | :: | |
3267 | ||
3268 | static int snd_xxx_open(struct snd_rawmidi_substream *substream); | |
3269 | ||
3270 | ||
3271 | This is called when a substream is opened. You can initialize the | |
3272 | hardware here, but you shouldn't start transmitting/receiving data yet. | |
3273 | ||
3274 | RawMIDI close callback | |
3275 | ~~~~~~~~~~~~~~~~~~~~~~ | |
3276 | ||
3277 | :: | |
3278 | ||
3279 | static int snd_xxx_close(struct snd_rawmidi_substream *substream); | |
3280 | ||
3281 | Guess what. | |
3282 | ||
3283 | The ``open`` and ``close`` callbacks of a rawmidi device are | |
3284 | serialized with a mutex, and can sleep. | |
3285 | ||
3286 | Rawmidi trigger callback for output substreams | |
3287 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
3288 | ||
3289 | :: | |
3290 | ||
3291 | static void snd_xxx_output_trigger(struct snd_rawmidi_substream *substream, int up); | |
3292 | ||
3293 | ||
3294 | This is called with a nonzero ``up`` parameter when there is some data | |
3295 | in the substream buffer that must be transmitted. | |
3296 | ||
3297 | To read data from the buffer, call | |
3298 | :c:func:`snd_rawmidi_transmit_peek()`. It will return the number | |
3299 | of bytes that have been read; this will be less than the number of bytes | |
3300 | requested when there are no more data in the buffer. After the data have | |
3301 | been transmitted successfully, call | |
3302 | :c:func:`snd_rawmidi_transmit_ack()` to remove the data from the | |
3303 | substream buffer: | |
3304 | ||
3305 | :: | |
3306 | ||
3307 | unsigned char data; | |
3308 | while (snd_rawmidi_transmit_peek(substream, &data, 1) == 1) { | |
3309 | if (snd_mychip_try_to_transmit(data)) | |
3310 | snd_rawmidi_transmit_ack(substream, 1); | |
3311 | else | |
3312 | break; /* hardware FIFO full */ | |
3313 | } | |
3314 | ||
3315 | If you know beforehand that the hardware will accept data, you can use | |
3316 | the :c:func:`snd_rawmidi_transmit()` function which reads some | |
3317 | data and removes them from the buffer at once: | |
3318 | ||
3319 | :: | |
3320 | ||
3321 | while (snd_mychip_transmit_possible()) { | |
3322 | unsigned char data; | |
3323 | if (snd_rawmidi_transmit(substream, &data, 1) != 1) | |
3324 | break; /* no more data */ | |
3325 | snd_mychip_transmit(data); | |
3326 | } | |
3327 | ||
3328 | If you know beforehand how many bytes you can accept, you can use a | |
3329 | buffer size greater than one with the | |
3330 | :c:func:`snd_rawmidi_transmit\*()` functions. | |
3331 | ||
3332 | The ``trigger`` callback must not sleep. If the hardware FIFO is full | |
3333 | before the substream buffer has been emptied, you have to continue | |
3334 | transmitting data later, either in an interrupt handler, or with a | |
3335 | timer if the hardware doesn't have a MIDI transmit interrupt. | |
3336 | ||
3337 | The ``trigger`` callback is called with a zero ``up`` parameter when | |
3338 | the transmission of data should be aborted. | |
3339 | ||
3340 | RawMIDI trigger callback for input substreams | |
3341 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
3342 | ||
3343 | :: | |
3344 | ||
3345 | static void snd_xxx_input_trigger(struct snd_rawmidi_substream *substream, int up); | |
3346 | ||
3347 | ||
3348 | This is called with a nonzero ``up`` parameter to enable receiving data, | |
3349 | or with a zero ``up`` parameter do disable receiving data. | |
3350 | ||
3351 | The ``trigger`` callback must not sleep; the actual reading of data | |
3352 | from the device is usually done in an interrupt handler. | |
3353 | ||
3354 | When data reception is enabled, your interrupt handler should call | |
3355 | :c:func:`snd_rawmidi_receive()` for all received data: | |
3356 | ||
3357 | :: | |
3358 | ||
3359 | void snd_mychip_midi_interrupt(...) | |
3360 | { | |
3361 | while (mychip_midi_available()) { | |
3362 | unsigned char data; | |
3363 | data = mychip_midi_read(); | |
3364 | snd_rawmidi_receive(substream, &data, 1); | |
3365 | } | |
3366 | } | |
3367 | ||
3368 | ||
3369 | drain callback | |
3370 | ~~~~~~~~~~~~~~ | |
3371 | ||
3372 | :: | |
3373 | ||
3374 | static void snd_xxx_drain(struct snd_rawmidi_substream *substream); | |
3375 | ||
3376 | ||
3377 | This is only used with output substreams. This function should wait | |
3378 | until all data read from the substream buffer have been transmitted. | |
3379 | This ensures that the device can be closed and the driver unloaded | |
3380 | without losing data. | |
3381 | ||
3382 | This callback is optional. If you do not set ``drain`` in the struct | |
3383 | snd_rawmidi_ops structure, ALSA will simply wait for 50 milliseconds | |
3384 | instead. | |
3385 | ||
3386 | Miscellaneous Devices | |
3387 | ===================== | |
3388 | ||
3389 | FM OPL3 | |
3390 | ------- | |
3391 | ||
3392 | The FM OPL3 is still used in many chips (mainly for backward | |
3393 | compatibility). ALSA has a nice OPL3 FM control layer, too. The OPL3 API | |
3394 | is defined in ``<sound/opl3.h>``. | |
3395 | ||
3396 | FM registers can be directly accessed through the direct-FM API, defined | |
3397 | in ``<sound/asound_fm.h>``. In ALSA native mode, FM registers are | |
3398 | accessed through the Hardware-Dependent Device direct-FM extension API, | |
3399 | whereas in OSS compatible mode, FM registers can be accessed with the | |
3400 | OSS direct-FM compatible API in ``/dev/dmfmX`` device. | |
3401 | ||
3402 | To create the OPL3 component, you have two functions to call. The first | |
3403 | one is a constructor for the ``opl3_t`` instance. | |
3404 | ||
3405 | :: | |
3406 | ||
3407 | struct snd_opl3 *opl3; | |
3408 | snd_opl3_create(card, lport, rport, OPL3_HW_OPL3_XXX, | |
3409 | integrated, &opl3); | |
3410 | ||
3411 | The first argument is the card pointer, the second one is the left port | |
3412 | address, and the third is the right port address. In most cases, the | |
3413 | right port is placed at the left port + 2. | |
3414 | ||
3415 | The fourth argument is the hardware type. | |
3416 | ||
3417 | When the left and right ports have been already allocated by the card | |
3418 | driver, pass non-zero to the fifth argument (``integrated``). Otherwise, | |
3419 | the opl3 module will allocate the specified ports by itself. | |
3420 | ||
3421 | When the accessing the hardware requires special method instead of the | |
3422 | standard I/O access, you can create opl3 instance separately with | |
3423 | :c:func:`snd_opl3_new()`. | |
3424 | ||
3425 | :: | |
3426 | ||
3427 | struct snd_opl3 *opl3; | |
3428 | snd_opl3_new(card, OPL3_HW_OPL3_XXX, &opl3); | |
3429 | ||
3430 | Then set ``command``, ``private_data`` and ``private_free`` for the | |
3431 | private access function, the private data and the destructor. The | |
3432 | ``l_port`` and ``r_port`` are not necessarily set. Only the command | |
3433 | must be set properly. You can retrieve the data from the | |
3434 | ``opl3->private_data`` field. | |
3435 | ||
3436 | After creating the opl3 instance via :c:func:`snd_opl3_new()`, | |
3437 | call :c:func:`snd_opl3_init()` to initialize the chip to the | |
3438 | proper state. Note that :c:func:`snd_opl3_create()` always calls | |
3439 | it internally. | |
3440 | ||
3441 | If the opl3 instance is created successfully, then create a hwdep device | |
3442 | for this opl3. | |
3443 | ||
3444 | :: | |
3445 | ||
3446 | struct snd_hwdep *opl3hwdep; | |
3447 | snd_opl3_hwdep_new(opl3, 0, 1, &opl3hwdep); | |
3448 | ||
3449 | The first argument is the ``opl3_t`` instance you created, and the | |
3450 | second is the index number, usually 0. | |
3451 | ||
3452 | The third argument is the index-offset for the sequencer client assigned | |
3453 | to the OPL3 port. When there is an MPU401-UART, give 1 for here (UART | |
3454 | always takes 0). | |
3455 | ||
3456 | Hardware-Dependent Devices | |
3457 | -------------------------- | |
3458 | ||
3459 | Some chips need user-space access for special controls or for loading | |
3460 | the micro code. In such a case, you can create a hwdep | |
3461 | (hardware-dependent) device. The hwdep API is defined in | |
3462 | ``<sound/hwdep.h>``. You can find examples in opl3 driver or | |
3463 | ``isa/sb/sb16_csp.c``. | |
3464 | ||
3465 | The creation of the ``hwdep`` instance is done via | |
3466 | :c:func:`snd_hwdep_new()`. | |
3467 | ||
3468 | :: | |
3469 | ||
3470 | struct snd_hwdep *hw; | |
3471 | snd_hwdep_new(card, "My HWDEP", 0, &hw); | |
3472 | ||
3473 | where the third argument is the index number. | |
3474 | ||
3475 | You can then pass any pointer value to the ``private_data``. If you | |
3476 | assign a private data, you should define the destructor, too. The | |
3477 | destructor function is set in the ``private_free`` field. | |
3478 | ||
3479 | :: | |
3480 | ||
3481 | struct mydata *p = kmalloc(sizeof(*p), GFP_KERNEL); | |
3482 | hw->private_data = p; | |
3483 | hw->private_free = mydata_free; | |
3484 | ||
3485 | and the implementation of the destructor would be: | |
3486 | ||
3487 | :: | |
3488 | ||
3489 | static void mydata_free(struct snd_hwdep *hw) | |
3490 | { | |
3491 | struct mydata *p = hw->private_data; | |
3492 | kfree(p); | |
3493 | } | |
3494 | ||
3495 | The arbitrary file operations can be defined for this instance. The file | |
3496 | operators are defined in the ``ops`` table. For example, assume that | |
3497 | this chip needs an ioctl. | |
3498 | ||
3499 | :: | |
3500 | ||
3501 | hw->ops.open = mydata_open; | |
3502 | hw->ops.ioctl = mydata_ioctl; | |
3503 | hw->ops.release = mydata_release; | |
3504 | ||
3505 | And implement the callback functions as you like. | |
3506 | ||
3507 | IEC958 (S/PDIF) | |
3508 | --------------- | |
3509 | ||
3510 | Usually the controls for IEC958 devices are implemented via the control | |
3511 | interface. There is a macro to compose a name string for IEC958 | |
3512 | controls, :c:func:`SNDRV_CTL_NAME_IEC958()` defined in | |
3513 | ``<include/asound.h>``. | |
3514 | ||
3515 | There are some standard controls for IEC958 status bits. These controls | |
3516 | use the type ``SNDRV_CTL_ELEM_TYPE_IEC958``, and the size of element is | |
3517 | fixed as 4 bytes array (value.iec958.status[x]). For the ``info`` | |
3518 | callback, you don't specify the value field for this type (the count | |
3519 | field must be set, though). | |
3520 | ||
3521 | “IEC958 Playback Con Mask” is used to return the bit-mask for the IEC958 | |
3522 | status bits of consumer mode. Similarly, “IEC958 Playback Pro Mask” | |
3523 | returns the bitmask for professional mode. They are read-only controls, | |
3524 | and are defined as MIXER controls (iface = | |
3525 | ``SNDRV_CTL_ELEM_IFACE_MIXER``). | |
3526 | ||
3527 | Meanwhile, “IEC958 Playback Default” control is defined for getting and | |
3528 | setting the current default IEC958 bits. Note that this one is usually | |
3529 | defined as a PCM control (iface = ``SNDRV_CTL_ELEM_IFACE_PCM``), | |
3530 | although in some places it's defined as a MIXER control. | |
3531 | ||
3532 | In addition, you can define the control switches to enable/disable or to | |
3533 | set the raw bit mode. The implementation will depend on the chip, but | |
3534 | the control should be named as “IEC958 xxx”, preferably using the | |
3535 | :c:func:`SNDRV_CTL_NAME_IEC958()` macro. | |
3536 | ||
3537 | You can find several cases, for example, ``pci/emu10k1``, | |
3538 | ``pci/ice1712``, or ``pci/cmipci.c``. | |
3539 | ||
3540 | Buffer and Memory Management | |
3541 | ============================ | |
3542 | ||
3543 | Buffer Types | |
3544 | ------------ | |
3545 | ||
3546 | ALSA provides several different buffer allocation functions depending on | |
3547 | the bus and the architecture. All these have a consistent API. The | |
3548 | allocation of physically-contiguous pages is done via | |
3549 | :c:func:`snd_malloc_xxx_pages()` function, where xxx is the bus | |
3550 | type. | |
3551 | ||
3552 | The allocation of pages with fallback is | |
3553 | :c:func:`snd_malloc_xxx_pages_fallback()`. This function tries | |
3554 | to allocate the specified pages but if the pages are not available, it | |
3555 | tries to reduce the page sizes until enough space is found. | |
3556 | ||
3557 | The release the pages, call :c:func:`snd_free_xxx_pages()` | |
3558 | function. | |
3559 | ||
3560 | Usually, ALSA drivers try to allocate and reserve a large contiguous | |
3561 | physical space at the time the module is loaded for the later use. This | |
3562 | is called “pre-allocation”. As already written, you can call the | |
3563 | following function at pcm instance construction time (in the case of PCI | |
3564 | bus). | |
3565 | ||
3566 | :: | |
3567 | ||
3568 | snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV, | |
b65f131b | 3569 | &pci->dev, size, max); |
7ddedebb TI |
3570 | |
3571 | where ``size`` is the byte size to be pre-allocated and the ``max`` is | |
3572 | the maximum size to be changed via the ``prealloc`` proc file. The | |
3573 | allocator will try to get an area as large as possible within the | |
3574 | given size. | |
3575 | ||
3576 | The second argument (type) and the third argument (device pointer) are | |
0b6a2c9c TI |
3577 | dependent on the bus. For normal devices, pass the device pointer |
3578 | (typically identical as ``card->dev``) to the third argument with | |
7ddedebb | 3579 | ``SNDRV_DMA_TYPE_DEV`` type. For the continuous buffer unrelated to the |
08422d2c TI |
3580 | bus can be pre-allocated with ``SNDRV_DMA_TYPE_CONTINUOUS`` type. |
3581 | You can pass NULL to the device pointer in that case, which is the | |
3582 | default mode implying to allocate with ``GFP_KRENEL`` flag. | |
3583 | If you need a different GFP flag, you can pass it by encoding the flag | |
3584 | into the device pointer via a special macro | |
3585 | :c:func:`snd_dma_continuous_data()`. | |
3586 | For the scatter-gather buffers, use ``SNDRV_DMA_TYPE_DEV_SG`` with the | |
3587 | device pointer (see the `Non-Contiguous Buffers`_ section). | |
7ddedebb TI |
3588 | |
3589 | Once the buffer is pre-allocated, you can use the allocator in the | |
3590 | ``hw_params`` callback: | |
3591 | ||
3592 | :: | |
3593 | ||
3594 | snd_pcm_lib_malloc_pages(substream, size); | |
3595 | ||
3596 | Note that you have to pre-allocate to use this function. | |
3597 | ||
72b4bcbf TI |
3598 | Most of drivers use, though, rather the newly introduced "managed |
3599 | buffer allocation mode" instead of the manual allocation or release. | |
3600 | This is done by calling :c:func:`snd_pcm_set_managed_buffer_all()` | |
3601 | instead of :c:func:`snd_pcm_lib_preallocate_pages_for_all()`. | |
3602 | ||
3603 | :: | |
3604 | ||
3605 | snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_DEV, | |
3606 | &pci->dev, size, max); | |
3607 | ||
3608 | where passed arguments are identical in both functions. | |
3609 | The difference in the managed mode is that PCM core will call | |
3610 | :c:func:`snd_pcm_lib_malloc_pages()` internally already before calling | |
3611 | the PCM ``hw_params`` callback, and call :c:func:`snd_pcm_lib_free_pages()` | |
3612 | after the PCM ``hw_free`` callback automatically. So the driver | |
3613 | doesn't have to call these functions explicitly in its callback any | |
3614 | longer. This made many driver code having NULL ``hw_params`` and | |
3615 | ``hw_free`` entries. | |
3616 | ||
7ddedebb TI |
3617 | External Hardware Buffers |
3618 | ------------------------- | |
3619 | ||
3620 | Some chips have their own hardware buffers and the DMA transfer from the | |
3621 | host memory is not available. In such a case, you need to either 1) | |
3622 | copy/set the audio data directly to the external hardware buffer, or 2) | |
3623 | make an intermediate buffer and copy/set the data from it to the | |
3624 | external hardware buffer in interrupts (or in tasklets, preferably). | |
3625 | ||
3626 | The first case works fine if the external hardware buffer is large | |
3627 | enough. This method doesn't need any extra buffers and thus is more | |
f7a47817 TI |
3628 | effective. You need to define the ``copy_user`` and ``copy_kernel`` |
3629 | callbacks for the data transfer, in addition to ``fill_silence`` | |
3630 | callback for playback. However, there is a drawback: it cannot be | |
7ddedebb TI |
3631 | mmapped. The examples are GUS's GF1 PCM or emu8000's wavetable PCM. |
3632 | ||
3633 | The second case allows for mmap on the buffer, although you have to | |
3634 | handle an interrupt or a tasklet to transfer the data from the | |
3635 | intermediate buffer to the hardware buffer. You can find an example in | |
3636 | the vxpocket driver. | |
3637 | ||
3638 | Another case is when the chip uses a PCI memory-map region for the | |
3639 | buffer instead of the host memory. In this case, mmap is available only | |
3640 | on certain architectures like the Intel one. In non-mmap mode, the data | |
3641 | cannot be transferred as in the normal way. Thus you need to define the | |
f7a47817 TI |
3642 | ``copy_user``, ``copy_kernel`` and ``fill_silence`` callbacks as well, |
3643 | as in the cases above. The examples are found in ``rme32.c`` and | |
3644 | ``rme96.c``. | |
7ddedebb | 3645 | |
f7a47817 TI |
3646 | The implementation of the ``copy_user``, ``copy_kernel`` and |
3647 | ``silence`` callbacks depends upon whether the hardware supports | |
3648 | interleaved or non-interleaved samples. The ``copy_user`` callback is | |
3649 | defined like below, a bit differently depending whether the direction | |
3650 | is playback or capture: | |
7ddedebb TI |
3651 | |
3652 | :: | |
3653 | ||
f7a47817 TI |
3654 | static int playback_copy_user(struct snd_pcm_substream *substream, |
3655 | int channel, unsigned long pos, | |
3656 | void __user *src, unsigned long count); | |
3657 | static int capture_copy_user(struct snd_pcm_substream *substream, | |
3658 | int channel, unsigned long pos, | |
3659 | void __user *dst, unsigned long count); | |
7ddedebb TI |
3660 | |
3661 | In the case of interleaved samples, the second argument (``channel``) is | |
3662 | not used. The third argument (``pos``) points the current position | |
f7a47817 | 3663 | offset in bytes. |
7ddedebb TI |
3664 | |
3665 | The meaning of the fourth argument is different between playback and | |
3666 | capture. For playback, it holds the source data pointer, and for | |
3667 | capture, it's the destination data pointer. | |
3668 | ||
f7a47817 | 3669 | The last argument is the number of bytes to be copied. |
7ddedebb TI |
3670 | |
3671 | What you have to do in this callback is again different between playback | |
3672 | and capture directions. In the playback case, you copy the given amount | |
3673 | of data (``count``) at the specified pointer (``src``) to the specified | |
3674 | offset (``pos``) on the hardware buffer. When coded like memcpy-like | |
3675 | way, the copy would be like: | |
3676 | ||
3677 | :: | |
3678 | ||
f7a47817 | 3679 | my_memcpy_from_user(my_buffer + pos, src, count); |
7ddedebb TI |
3680 | |
3681 | For the capture direction, you copy the given amount of data (``count``) | |
3682 | at the specified offset (``pos``) on the hardware buffer to the | |
3683 | specified pointer (``dst``). | |
3684 | ||
3685 | :: | |
3686 | ||
f7a47817 TI |
3687 | my_memcpy_to_user(dst, my_buffer + pos, count); |
3688 | ||
3689 | Here the functions are named as ``from_user`` and ``to_user`` because | |
3690 | it's the user-space buffer that is passed to these callbacks. That | |
3691 | is, the callback is supposed to copy from/to the user-space data | |
3692 | directly to/from the hardware buffer. | |
7ddedebb | 3693 | |
f7a47817 TI |
3694 | Careful readers might notice that these callbacks receive the |
3695 | arguments in bytes, not in frames like other callbacks. It's because | |
3696 | it would make coding easier like the examples above, and also it makes | |
3697 | easier to unify both the interleaved and non-interleaved cases, as | |
3698 | explained in the following. | |
7ddedebb TI |
3699 | |
3700 | In the case of non-interleaved samples, the implementation will be a bit | |
f7a47817 TI |
3701 | more complicated. The callback is called for each channel, passed by |
3702 | the second argument, so totally it's called for N-channels times per | |
3703 | transfer. | |
3704 | ||
3705 | The meaning of other arguments are almost same as the interleaved | |
3706 | case. The callback is supposed to copy the data from/to the given | |
3707 | user-space buffer, but only for the given channel. For the detailed | |
3708 | implementations, please check ``isa/gus/gus_pcm.c`` or | |
3709 | "pci/rme9652/rme9652.c" as examples. | |
3710 | ||
3711 | The above callbacks are the copy from/to the user-space buffer. There | |
3712 | are some cases where we want copy from/to the kernel-space buffer | |
3713 | instead. In such a case, ``copy_kernel`` callback is called. It'd | |
3714 | look like: | |
3715 | ||
3716 | :: | |
3717 | ||
3718 | static int playback_copy_kernel(struct snd_pcm_substream *substream, | |
3719 | int channel, unsigned long pos, | |
3720 | void *src, unsigned long count); | |
3721 | static int capture_copy_kernel(struct snd_pcm_substream *substream, | |
3722 | int channel, unsigned long pos, | |
3723 | void *dst, unsigned long count); | |
3724 | ||
3725 | As found easily, the only difference is that the buffer pointer is | |
3726 | without ``__user`` prefix; that is, a kernel-buffer pointer is passed | |
3727 | in the fourth argument. Correspondingly, the implementation would be | |
3728 | a version without the user-copy, such as: | |
7ddedebb | 3729 | |
f7a47817 TI |
3730 | :: |
3731 | ||
3732 | my_memcpy(my_buffer + pos, src, count); | |
7ddedebb | 3733 | |
f7a47817 TI |
3734 | Usually for the playback, another callback ``fill_silence`` is |
3735 | defined. It's implemented in a similar way as the copy callbacks | |
3736 | above: | |
7ddedebb TI |
3737 | |
3738 | :: | |
3739 | ||
3740 | static int silence(struct snd_pcm_substream *substream, int channel, | |
f7a47817 | 3741 | unsigned long pos, unsigned long count); |
7ddedebb | 3742 | |
f7a47817 TI |
3743 | The meanings of arguments are the same as in the ``copy_user`` and |
3744 | ``copy_kernel`` callbacks, although there is no buffer pointer | |
3745 | argument. In the case of interleaved samples, the channel argument has | |
3746 | no meaning, as well as on ``copy_*`` callbacks. | |
7ddedebb | 3747 | |
f7a47817 | 3748 | The role of ``fill_silence`` callback is to set the given amount |
7ddedebb TI |
3749 | (``count``) of silence data at the specified offset (``pos``) on the |
3750 | hardware buffer. Suppose that the data format is signed (that is, the | |
3751 | silent-data is 0), and the implementation using a memset-like function | |
3752 | would be like: | |
3753 | ||
3754 | :: | |
3755 | ||
f7a47817 | 3756 | my_memset(my_buffer + pos, 0, count); |
7ddedebb TI |
3757 | |
3758 | In the case of non-interleaved samples, again, the implementation | |
f7a47817 TI |
3759 | becomes a bit more complicated, as it's called N-times per transfer |
3760 | for each channel. See, for example, ``isa/gus/gus_pcm.c``. | |
7ddedebb TI |
3761 | |
3762 | Non-Contiguous Buffers | |
3763 | ---------------------- | |
3764 | ||
3765 | If your hardware supports the page table as in emu10k1 or the buffer | |
3766 | descriptors as in via82xx, you can use the scatter-gather (SG) DMA. ALSA | |
3767 | provides an interface for handling SG-buffers. The API is provided in | |
3768 | ``<sound/pcm.h>``. | |
3769 | ||
3770 | For creating the SG-buffer handler, call | |
72b4bcbf TI |
3771 | :c:func:`snd_pcm_set_managed_buffer()` or |
3772 | :c:func:`snd_pcm_set_managed_buffer_all()` with | |
7ddedebb | 3773 | ``SNDRV_DMA_TYPE_DEV_SG`` in the PCM constructor like other PCI |
b65f131b | 3774 | pre-allocator. You need to pass ``&pci->dev``, where pci is |
7ddedebb | 3775 | the :c:type:`struct pci_dev <pci_dev>` pointer of the chip as |
abffd8d0 TI |
3776 | well. |
3777 | ||
3778 | :: | |
3779 | ||
72b4bcbf TI |
3780 | snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_DEV_SG, |
3781 | &pci->dev, size, max); | |
abffd8d0 TI |
3782 | |
3783 | The ``struct snd_sg_buf`` instance is created as | |
3784 | ``substream->dma_private`` in turn. You can cast the pointer like: | |
7ddedebb TI |
3785 | |
3786 | :: | |
3787 | ||
3788 | struct snd_sg_buf *sgbuf = (struct snd_sg_buf *)substream->dma_private; | |
3789 | ||
72b4bcbf | 3790 | Then in :c:func:`snd_pcm_lib_malloc_pages()` call, the common SG-buffer |
7ddedebb TI |
3791 | handler will allocate the non-contiguous kernel pages of the given size |
3792 | and map them onto the virtually contiguous memory. The virtual pointer | |
3793 | is addressed in runtime->dma_area. The physical address | |
3794 | (``runtime->dma_addr``) is set to zero, because the buffer is | |
3795 | physically non-contiguous. The physical address table is set up in | |
3796 | ``sgbuf->table``. You can get the physical address at a certain offset | |
3797 | via :c:func:`snd_pcm_sgbuf_get_addr()`. | |
3798 | ||
72b4bcbf TI |
3799 | If you need to release the SG-buffer data explicitly, call the |
3800 | standard API function :c:func:`snd_pcm_lib_free_pages()` as usual. | |
7ddedebb TI |
3801 | |
3802 | Vmalloc'ed Buffers | |
3803 | ------------------ | |
3804 | ||
3805 | It's possible to use a buffer allocated via :c:func:`vmalloc()`, for | |
abffd8d0 TI |
3806 | example, for an intermediate buffer. In the recent version of kernel, |
3807 | you can simply allocate it via standard | |
3808 | :c:func:`snd_pcm_lib_malloc_pages()` and co after setting up the | |
3809 | buffer preallocation with ``SNDRV_DMA_TYPE_VMALLOC`` type. | |
7ddedebb | 3810 | |
abffd8d0 | 3811 | :: |
f90afe79 | 3812 | |
72b4bcbf TI |
3813 | snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_VMALLOC, |
3814 | NULL, 0, 0); | |
7ddedebb | 3815 | |
abffd8d0 TI |
3816 | The NULL is passed to the device pointer argument, which indicates |
3817 | that the default pages (GFP_KERNEL and GFP_HIGHMEM) will be | |
3818 | allocated. | |
7ddedebb | 3819 | |
abffd8d0 TI |
3820 | Also, note that zero is passed to both the size and the max size |
3821 | arguments here. Since each vmalloc call should succeed at any time, | |
3822 | we don't need to pre-allocate the buffers like other continuous | |
3823 | pages. | |
7ddedebb | 3824 | |
abffd8d0 TI |
3825 | If you need the 32bit DMA allocation, pass the device pointer encoded |
3826 | by :c:func:`snd_dma_continuous_data()` with ``GFP_KERNEL|__GFP_DMA32`` | |
3827 | argument. | |
3828 | ||
3829 | :: | |
3830 | ||
72b4bcbf | 3831 | snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_VMALLOC, |
abffd8d0 | 3832 | snd_dma_continuous_data(GFP_KERNEL | __GFP_DMA32), 0, 0); |
7ddedebb TI |
3833 | |
3834 | Proc Interface | |
3835 | ============== | |
3836 | ||
3837 | ALSA provides an easy interface for procfs. The proc files are very | |
3838 | useful for debugging. I recommend you set up proc files if you write a | |
3839 | driver and want to get a running status or register dumps. The API is | |
3840 | found in ``<sound/info.h>``. | |
3841 | ||
3842 | To create a proc file, call :c:func:`snd_card_proc_new()`. | |
3843 | ||
3844 | :: | |
3845 | ||
3846 | struct snd_info_entry *entry; | |
3847 | int err = snd_card_proc_new(card, "my-file", &entry); | |
3848 | ||
3849 | where the second argument specifies the name of the proc file to be | |
3850 | created. The above example will create a file ``my-file`` under the | |
3851 | card directory, e.g. ``/proc/asound/card0/my-file``. | |
3852 | ||
3853 | Like other components, the proc entry created via | |
3854 | :c:func:`snd_card_proc_new()` will be registered and released | |
3855 | automatically in the card registration and release functions. | |
3856 | ||
3857 | When the creation is successful, the function stores a new instance in | |
3858 | the pointer given in the third argument. It is initialized as a text | |
3859 | proc file for read only. To use this proc file as a read-only text file | |
3860 | as it is, set the read callback with a private data via | |
3861 | :c:func:`snd_info_set_text_ops()`. | |
3862 | ||
3863 | :: | |
3864 | ||
3865 | snd_info_set_text_ops(entry, chip, my_proc_read); | |
3866 | ||
3867 | where the second argument (``chip``) is the private data to be used in | |
3868 | the callbacks. The third parameter specifies the read buffer size and | |
3869 | the fourth (``my_proc_read``) is the callback function, which is | |
3870 | defined like | |
3871 | ||
3872 | :: | |
3873 | ||
3874 | static void my_proc_read(struct snd_info_entry *entry, | |
3875 | struct snd_info_buffer *buffer); | |
3876 | ||
3877 | In the read callback, use :c:func:`snd_iprintf()` for output | |
3878 | strings, which works just like normal :c:func:`printf()`. For | |
3879 | example, | |
3880 | ||
3881 | :: | |
3882 | ||
3883 | static void my_proc_read(struct snd_info_entry *entry, | |
3884 | struct snd_info_buffer *buffer) | |
3885 | { | |
3886 | struct my_chip *chip = entry->private_data; | |
3887 | ||
3888 | snd_iprintf(buffer, "This is my chip!\n"); | |
3889 | snd_iprintf(buffer, "Port = %ld\n", chip->port); | |
3890 | } | |
3891 | ||
3892 | The file permissions can be changed afterwards. As default, it's set as | |
3893 | read only for all users. If you want to add write permission for the | |
3894 | user (root as default), do as follows: | |
3895 | ||
3896 | :: | |
3897 | ||
3898 | entry->mode = S_IFREG | S_IRUGO | S_IWUSR; | |
3899 | ||
3900 | and set the write buffer size and the callback | |
3901 | ||
3902 | :: | |
3903 | ||
3904 | entry->c.text.write = my_proc_write; | |
3905 | ||
3906 | For the write callback, you can use :c:func:`snd_info_get_line()` | |
3907 | to get a text line, and :c:func:`snd_info_get_str()` to retrieve | |
3908 | a string from the line. Some examples are found in | |
3909 | ``core/oss/mixer_oss.c``, core/oss/and ``pcm_oss.c``. | |
3910 | ||
3911 | For a raw-data proc-file, set the attributes as follows: | |
3912 | ||
3913 | :: | |
3914 | ||
3915 | static struct snd_info_entry_ops my_file_io_ops = { | |
3916 | .read = my_file_io_read, | |
3917 | }; | |
3918 | ||
3919 | entry->content = SNDRV_INFO_CONTENT_DATA; | |
3920 | entry->private_data = chip; | |
3921 | entry->c.ops = &my_file_io_ops; | |
3922 | entry->size = 4096; | |
3923 | entry->mode = S_IFREG | S_IRUGO; | |
3924 | ||
3925 | For the raw data, ``size`` field must be set properly. This specifies | |
3926 | the maximum size of the proc file access. | |
3927 | ||
3928 | The read/write callbacks of raw mode are more direct than the text mode. | |
3929 | You need to use a low-level I/O functions such as | |
3930 | :c:func:`copy_from/to_user()` to transfer the data. | |
3931 | ||
3932 | :: | |
3933 | ||
3934 | static ssize_t my_file_io_read(struct snd_info_entry *entry, | |
3935 | void *file_private_data, | |
3936 | struct file *file, | |
3937 | char *buf, | |
3938 | size_t count, | |
3939 | loff_t pos) | |
3940 | { | |
3941 | if (copy_to_user(buf, local_data + pos, count)) | |
3942 | return -EFAULT; | |
3943 | return count; | |
3944 | } | |
3945 | ||
3946 | If the size of the info entry has been set up properly, ``count`` and | |
3947 | ``pos`` are guaranteed to fit within 0 and the given size. You don't | |
3948 | have to check the range in the callbacks unless any other condition is | |
3949 | required. | |
3950 | ||
3951 | Power Management | |
3952 | ================ | |
3953 | ||
3954 | If the chip is supposed to work with suspend/resume functions, you need | |
3955 | to add power-management code to the driver. The additional code for | |
f90afe79 TI |
3956 | power-management should be ifdef-ed with ``CONFIG_PM``, or annotated |
3957 | with __maybe_unused attribute; otherwise the compiler will complain | |
3958 | you. | |
7ddedebb TI |
3959 | |
3960 | If the driver *fully* supports suspend/resume that is, the device can be | |
3961 | properly resumed to its state when suspend was called, you can set the | |
3962 | ``SNDRV_PCM_INFO_RESUME`` flag in the pcm info field. Usually, this is | |
3963 | possible when the registers of the chip can be safely saved and restored | |
3964 | to RAM. If this is set, the trigger callback is called with | |
3965 | ``SNDRV_PCM_TRIGGER_RESUME`` after the resume callback completes. | |
3966 | ||
3967 | Even if the driver doesn't support PM fully but partial suspend/resume | |
3968 | is still possible, it's still worthy to implement suspend/resume | |
3969 | callbacks. In such a case, applications would reset the status by | |
3970 | calling :c:func:`snd_pcm_prepare()` and restart the stream | |
3971 | appropriately. Hence, you can define suspend/resume callbacks below but | |
3972 | don't set ``SNDRV_PCM_INFO_RESUME`` info flag to the PCM. | |
3973 | ||
3974 | Note that the trigger with SUSPEND can always be called when | |
3975 | :c:func:`snd_pcm_suspend_all()` is called, regardless of the | |
3976 | ``SNDRV_PCM_INFO_RESUME`` flag. The ``RESUME`` flag affects only the | |
3977 | behavior of :c:func:`snd_pcm_resume()`. (Thus, in theory, | |
3978 | ``SNDRV_PCM_TRIGGER_RESUME`` isn't needed to be handled in the trigger | |
3979 | callback when no ``SNDRV_PCM_INFO_RESUME`` flag is set. But, it's better | |
3980 | to keep it for compatibility reasons.) | |
3981 | ||
3982 | In the earlier version of ALSA drivers, a common power-management layer | |
3983 | was provided, but it has been removed. The driver needs to define the | |
3984 | suspend/resume hooks according to the bus the device is connected to. In | |
3985 | the case of PCI drivers, the callbacks look like below: | |
3986 | ||
3987 | :: | |
3988 | ||
f90afe79 | 3989 | static int __maybe_unused snd_my_suspend(struct device *dev) |
7ddedebb TI |
3990 | { |
3991 | .... /* do things for suspend */ | |
3992 | return 0; | |
3993 | } | |
f90afe79 | 3994 | static int __maybe_unused snd_my_resume(struct device *dev) |
7ddedebb TI |
3995 | { |
3996 | .... /* do things for suspend */ | |
3997 | return 0; | |
3998 | } | |
7ddedebb TI |
3999 | |
4000 | The scheme of the real suspend job is as follows. | |
4001 | ||
4002 | 1. Retrieve the card and the chip data. | |
4003 | ||
4004 | 2. Call :c:func:`snd_power_change_state()` with | |
4005 | ``SNDRV_CTL_POWER_D3hot`` to change the power status. | |
4006 | ||
910e7e19 | 4007 | 3. If AC97 codecs are used, call :c:func:`snd_ac97_suspend()` for |
7ddedebb TI |
4008 | each codec. |
4009 | ||
910e7e19 | 4010 | 4. Save the register values if necessary. |
7ddedebb | 4011 | |
910e7e19 | 4012 | 5. Stop the hardware if necessary. |
7ddedebb | 4013 | |
7ddedebb TI |
4014 | A typical code would be like: |
4015 | ||
4016 | :: | |
4017 | ||
f90afe79 | 4018 | static int __maybe_unused mychip_suspend(struct device *dev) |
7ddedebb TI |
4019 | { |
4020 | /* (1) */ | |
f90afe79 | 4021 | struct snd_card *card = dev_get_drvdata(dev); |
7ddedebb TI |
4022 | struct mychip *chip = card->private_data; |
4023 | /* (2) */ | |
4024 | snd_power_change_state(card, SNDRV_CTL_POWER_D3hot); | |
4025 | /* (3) */ | |
7ddedebb | 4026 | snd_ac97_suspend(chip->ac97); |
910e7e19 | 4027 | /* (4) */ |
7ddedebb | 4028 | snd_mychip_save_registers(chip); |
910e7e19 | 4029 | /* (5) */ |
7ddedebb | 4030 | snd_mychip_stop_hardware(chip); |
7ddedebb TI |
4031 | return 0; |
4032 | } | |
4033 | ||
4034 | ||
4035 | The scheme of the real resume job is as follows. | |
4036 | ||
4037 | 1. Retrieve the card and the chip data. | |
4038 | ||
f90afe79 | 4039 | 2. Re-initialize the chip. |
7ddedebb | 4040 | |
f90afe79 | 4041 | 3. Restore the saved registers if necessary. |
7ddedebb | 4042 | |
f90afe79 | 4043 | 4. Resume the mixer, e.g. calling :c:func:`snd_ac97_resume()`. |
7ddedebb | 4044 | |
f90afe79 | 4045 | 5. Restart the hardware (if any). |
7ddedebb | 4046 | |
f90afe79 | 4047 | 6. Call :c:func:`snd_power_change_state()` with |
7ddedebb TI |
4048 | ``SNDRV_CTL_POWER_D0`` to notify the processes. |
4049 | ||
4050 | A typical code would be like: | |
4051 | ||
4052 | :: | |
4053 | ||
f90afe79 | 4054 | static int __maybe_unused mychip_resume(struct pci_dev *pci) |
7ddedebb TI |
4055 | { |
4056 | /* (1) */ | |
f90afe79 | 4057 | struct snd_card *card = dev_get_drvdata(dev); |
7ddedebb TI |
4058 | struct mychip *chip = card->private_data; |
4059 | /* (2) */ | |
7ddedebb | 4060 | snd_mychip_reinit_chip(chip); |
f90afe79 | 4061 | /* (3) */ |
7ddedebb | 4062 | snd_mychip_restore_registers(chip); |
f90afe79 | 4063 | /* (4) */ |
7ddedebb | 4064 | snd_ac97_resume(chip->ac97); |
f90afe79 | 4065 | /* (5) */ |
7ddedebb | 4066 | snd_mychip_restart_chip(chip); |
f90afe79 | 4067 | /* (6) */ |
7ddedebb TI |
4068 | snd_power_change_state(card, SNDRV_CTL_POWER_D0); |
4069 | return 0; | |
4070 | } | |
4071 | ||
910e7e19 TI |
4072 | Note that, at the time this callback gets called, the PCM stream has |
4073 | been already suspended via its own PM ops calling | |
4074 | :c:func:`snd_pcm_suspend_all()` internally. | |
7ddedebb TI |
4075 | |
4076 | OK, we have all callbacks now. Let's set them up. In the initialization | |
4077 | of the card, make sure that you can get the chip data from the card | |
4078 | instance, typically via ``private_data`` field, in case you created the | |
4079 | chip data individually. | |
4080 | ||
4081 | :: | |
4082 | ||
4083 | static int snd_mychip_probe(struct pci_dev *pci, | |
4084 | const struct pci_device_id *pci_id) | |
4085 | { | |
4086 | .... | |
4087 | struct snd_card *card; | |
4088 | struct mychip *chip; | |
4089 | int err; | |
4090 | .... | |
4091 | err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE, | |
4092 | 0, &card); | |
4093 | .... | |
4094 | chip = kzalloc(sizeof(*chip), GFP_KERNEL); | |
4095 | .... | |
4096 | card->private_data = chip; | |
4097 | .... | |
4098 | } | |
4099 | ||
4100 | When you created the chip data with :c:func:`snd_card_new()`, it's | |
4101 | anyway accessible via ``private_data`` field. | |
4102 | ||
4103 | :: | |
4104 | ||
4105 | static int snd_mychip_probe(struct pci_dev *pci, | |
4106 | const struct pci_device_id *pci_id) | |
4107 | { | |
4108 | .... | |
4109 | struct snd_card *card; | |
4110 | struct mychip *chip; | |
4111 | int err; | |
4112 | .... | |
4113 | err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE, | |
4114 | sizeof(struct mychip), &card); | |
4115 | .... | |
4116 | chip = card->private_data; | |
4117 | .... | |
4118 | } | |
4119 | ||
4120 | If you need a space to save the registers, allocate the buffer for it | |
4121 | here, too, since it would be fatal if you cannot allocate a memory in | |
4122 | the suspend phase. The allocated buffer should be released in the | |
4123 | corresponding destructor. | |
4124 | ||
4125 | And next, set suspend/resume callbacks to the pci_driver. | |
4126 | ||
4127 | :: | |
4128 | ||
f90afe79 TI |
4129 | static SIMPLE_DEV_PM_OPS(snd_my_pm_ops, mychip_suspend, mychip_resume); |
4130 | ||
7ddedebb TI |
4131 | static struct pci_driver driver = { |
4132 | .name = KBUILD_MODNAME, | |
4133 | .id_table = snd_my_ids, | |
4134 | .probe = snd_my_probe, | |
4135 | .remove = snd_my_remove, | |
f90afe79 | 4136 | .driver.pm = &snd_my_pm_ops, |
7ddedebb TI |
4137 | }; |
4138 | ||
4139 | Module Parameters | |
4140 | ================= | |
4141 | ||
4142 | There are standard module options for ALSA. At least, each module should | |
4143 | have the ``index``, ``id`` and ``enable`` options. | |
4144 | ||
4145 | If the module supports multiple cards (usually up to 8 = ``SNDRV_CARDS`` | |
4146 | cards), they should be arrays. The default initial values are defined | |
4147 | already as constants for easier programming: | |
4148 | ||
4149 | :: | |
4150 | ||
4151 | static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX; | |
4152 | static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR; | |
4153 | static int enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP; | |
4154 | ||
4155 | If the module supports only a single card, they could be single | |
4156 | variables, instead. ``enable`` option is not always necessary in this | |
4157 | case, but it would be better to have a dummy option for compatibility. | |
4158 | ||
4159 | The module parameters must be declared with the standard | |
f90afe79 | 4160 | ``module_param()``, ``module_param_array()`` and |
7ddedebb TI |
4161 | :c:func:`MODULE_PARM_DESC()` macros. |
4162 | ||
4163 | The typical coding would be like below: | |
4164 | ||
4165 | :: | |
4166 | ||
4167 | #define CARD_NAME "My Chip" | |
4168 | ||
4169 | module_param_array(index, int, NULL, 0444); | |
4170 | MODULE_PARM_DESC(index, "Index value for " CARD_NAME " soundcard."); | |
4171 | module_param_array(id, charp, NULL, 0444); | |
4172 | MODULE_PARM_DESC(id, "ID string for " CARD_NAME " soundcard."); | |
4173 | module_param_array(enable, bool, NULL, 0444); | |
4174 | MODULE_PARM_DESC(enable, "Enable " CARD_NAME " soundcard."); | |
4175 | ||
f90afe79 TI |
4176 | Also, don't forget to define the module description and the license. |
4177 | Especially, the recent modprobe requires to define the | |
7ddedebb TI |
4178 | module license as GPL, etc., otherwise the system is shown as “tainted”. |
4179 | ||
4180 | :: | |
4181 | ||
f90afe79 | 4182 | MODULE_DESCRIPTION("Sound driver for My Chip"); |
7ddedebb | 4183 | MODULE_LICENSE("GPL"); |
7ddedebb TI |
4184 | |
4185 | ||
4186 | How To Put Your Driver Into ALSA Tree | |
4187 | ===================================== | |
4188 | ||
4189 | General | |
4190 | ------- | |
4191 | ||
4192 | So far, you've learned how to write the driver codes. And you might have | |
4193 | a question now: how to put my own driver into the ALSA driver tree? Here | |
4194 | (finally :) the standard procedure is described briefly. | |
4195 | ||
4196 | Suppose that you create a new PCI driver for the card “xyz”. The card | |
4197 | module name would be snd-xyz. The new driver is usually put into the | |
f90afe79 TI |
4198 | alsa-driver tree, ``sound/pci`` directory in the case of PCI |
4199 | cards. | |
7ddedebb TI |
4200 | |
4201 | In the following sections, the driver code is supposed to be put into | |
f90afe79 | 4202 | Linux kernel tree. The two cases are covered: a driver consisting of a |
7ddedebb TI |
4203 | single source file and one consisting of several source files. |
4204 | ||
4205 | Driver with A Single Source File | |
4206 | -------------------------------- | |
4207 | ||
f90afe79 | 4208 | 1. Modify sound/pci/Makefile |
7ddedebb TI |
4209 | |
4210 | Suppose you have a file xyz.c. Add the following two lines | |
4211 | ||
4212 | :: | |
4213 | ||
4214 | snd-xyz-objs := xyz.o | |
4215 | obj-$(CONFIG_SND_XYZ) += snd-xyz.o | |
4216 | ||
4217 | 2. Create the Kconfig entry | |
4218 | ||
4219 | Add the new entry of Kconfig for your xyz driver. config SND_XYZ | |
4220 | tristate "Foobar XYZ" depends on SND select SND_PCM help Say Y here | |
4221 | to include support for Foobar XYZ soundcard. To compile this driver | |
4222 | as a module, choose M here: the module will be called snd-xyz. the | |
4223 | line, select SND_PCM, specifies that the driver xyz supports PCM. In | |
4224 | addition to SND_PCM, the following components are supported for | |
4225 | select command: SND_RAWMIDI, SND_TIMER, SND_HWDEP, | |
4226 | SND_MPU401_UART, SND_OPL3_LIB, SND_OPL4_LIB, SND_VX_LIB, | |
4227 | SND_AC97_CODEC. Add the select command for each supported | |
4228 | component. | |
4229 | ||
4230 | Note that some selections imply the lowlevel selections. For example, | |
4231 | PCM includes TIMER, MPU401_UART includes RAWMIDI, AC97_CODEC | |
4232 | includes PCM, and OPL3_LIB includes HWDEP. You don't need to give | |
4233 | the lowlevel selections again. | |
4234 | ||
4235 | For the details of Kconfig script, refer to the kbuild documentation. | |
4236 | ||
7ddedebb TI |
4237 | Drivers with Several Source Files |
4238 | --------------------------------- | |
4239 | ||
4240 | Suppose that the driver snd-xyz have several source files. They are | |
f90afe79 | 4241 | located in the new subdirectory, sound/pci/xyz. |
7ddedebb | 4242 | |
f90afe79 TI |
4243 | 1. Add a new directory (``sound/pci/xyz``) in ``sound/pci/Makefile`` |
4244 | as below | |
7ddedebb TI |
4245 | |
4246 | :: | |
4247 | ||
f90afe79 | 4248 | obj-$(CONFIG_SND) += sound/pci/xyz/ |
7ddedebb TI |
4249 | |
4250 | ||
f90afe79 | 4251 | 2. Under the directory ``sound/pci/xyz``, create a Makefile |
7ddedebb TI |
4252 | |
4253 | :: | |
4254 | ||
7ddedebb | 4255 | snd-xyz-objs := xyz.o abc.o def.o |
7ddedebb TI |
4256 | obj-$(CONFIG_SND_XYZ) += snd-xyz.o |
4257 | ||
7ddedebb TI |
4258 | 3. Create the Kconfig entry |
4259 | ||
4260 | This procedure is as same as in the last section. | |
4261 | ||
7ddedebb TI |
4262 | |
4263 | Useful Functions | |
4264 | ================ | |
4265 | ||
4266 | :c:func:`snd_printk()` and friends | |
f90afe79 TI |
4267 | ---------------------------------- |
4268 | ||
4269 | .. note:: This subsection describes a few helper functions for | |
4270 | decorating a bit more on the standard :c:func:`printk()` & co. | |
4271 | However, in general, the use of such helpers is no longer recommended. | |
4272 | If possible, try to stick with the standard functions like | |
4273 | :c:func:`dev_err()` or :c:func:`pr_err()`. | |
7ddedebb TI |
4274 | |
4275 | ALSA provides a verbose version of the :c:func:`printk()` function. | |
4276 | If a kernel config ``CONFIG_SND_VERBOSE_PRINTK`` is set, this function | |
4277 | prints the given message together with the file name and the line of the | |
4278 | caller. The ``KERN_XXX`` prefix is processed as well as the original | |
4279 | :c:func:`printk()` does, so it's recommended to add this prefix, | |
4280 | e.g. snd_printk(KERN_ERR "Oh my, sorry, it's extremely bad!\\n"); | |
4281 | ||
4282 | There are also :c:func:`printk()`'s for debugging. | |
4283 | :c:func:`snd_printd()` can be used for general debugging purposes. | |
4284 | If ``CONFIG_SND_DEBUG`` is set, this function is compiled, and works | |
4285 | just like :c:func:`snd_printk()`. If the ALSA is compiled without | |
4286 | the debugging flag, it's ignored. | |
4287 | ||
4288 | :c:func:`snd_printdd()` is compiled in only when | |
f90afe79 | 4289 | ``CONFIG_SND_DEBUG_VERBOSE`` is set. |
7ddedebb TI |
4290 | |
4291 | :c:func:`snd_BUG()` | |
f90afe79 | 4292 | ------------------- |
7ddedebb TI |
4293 | |
4294 | It shows the ``BUG?`` message and stack trace as well as | |
4295 | :c:func:`snd_BUG_ON()` at the point. It's useful to show that a | |
4296 | fatal error happens there. | |
4297 | ||
4298 | When no debug flag is set, this macro is ignored. | |
4299 | ||
4300 | :c:func:`snd_BUG_ON()` | |
f90afe79 | 4301 | ---------------------- |
7ddedebb TI |
4302 | |
4303 | :c:func:`snd_BUG_ON()` macro is similar with | |
4304 | :c:func:`WARN_ON()` macro. For example, snd_BUG_ON(!pointer); or | |
4305 | it can be used as the condition, if (snd_BUG_ON(non_zero_is_bug)) | |
4306 | return -EINVAL; | |
4307 | ||
4308 | The macro takes an conditional expression to evaluate. When | |
4309 | ``CONFIG_SND_DEBUG``, is set, if the expression is non-zero, it shows | |
4310 | the warning message such as ``BUG? (xxx)`` normally followed by stack | |
4311 | trace. In both cases it returns the evaluated value. | |
4312 | ||
4313 | Acknowledgments | |
4314 | =============== | |
4315 | ||
4316 | I would like to thank Phil Kerr for his help for improvement and | |
4317 | corrections of this document. | |
4318 | ||
4319 | Kevin Conder reformatted the original plain-text to the DocBook format. | |
4320 | ||
4321 | Giuliano Pochini corrected typos and contributed the example codes in | |
4322 | the hardware constraints section. |