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