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03158a70 MCC |
1 | ============================================ |
2 | Dynamic DMA mapping using the generic device | |
3 | ============================================ | |
1da177e4 | 4 | |
03158a70 | 5 | :Author: James E.J. Bottomley <James.Bottomley@HansenPartnership.com> |
1da177e4 LT |
6 | |
7 | This document describes the DMA API. For a more gentle introduction | |
77f2ea2f | 8 | of the API (and actual examples), see Documentation/DMA-API-HOWTO.txt. |
1da177e4 | 9 | |
77f2ea2f BH |
10 | This API is split into two pieces. Part I describes the basic API. |
11 | Part II describes extensions for supporting non-consistent memory | |
12 | machines. Unless you know that your driver absolutely has to support | |
13 | non-consistent platforms (this is usually only legacy platforms) you | |
14 | should only use the API described in part I. | |
1da177e4 | 15 | |
03158a70 MCC |
16 | Part I - dma_API |
17 | ---------------- | |
1da177e4 | 18 | |
03158a70 | 19 | To get the dma_API, you must #include <linux/dma-mapping.h>. This |
77f2ea2f | 20 | provides dma_addr_t and the interfaces described below. |
1da177e4 | 21 | |
3a9ad0b4 YL |
22 | A dma_addr_t can hold any valid DMA address for the platform. It can be |
23 | given to a device to use as a DMA source or target. A CPU cannot reference | |
24 | a dma_addr_t directly because there may be translation between its physical | |
25 | address space and the DMA address space. | |
1da177e4 | 26 | |
77f2ea2f | 27 | Part Ia - Using large DMA-coherent buffers |
1da177e4 LT |
28 | ------------------------------------------ |
29 | ||
03158a70 MCC |
30 | :: |
31 | ||
32 | void * | |
33 | dma_alloc_coherent(struct device *dev, size_t size, | |
34 | dma_addr_t *dma_handle, gfp_t flag) | |
1da177e4 LT |
35 | |
36 | Consistent memory is memory for which a write by either the device or | |
37 | the processor can immediately be read by the processor or device | |
21440d31 DB |
38 | without having to worry about caching effects. (You may however need |
39 | to make sure to flush the processor's write buffers before telling | |
40 | devices to read that memory.) | |
1da177e4 LT |
41 | |
42 | This routine allocates a region of <size> bytes of consistent memory. | |
1da177e4 | 43 | |
77f2ea2f | 44 | It returns a pointer to the allocated region (in the processor's virtual |
1da177e4 LT |
45 | address space) or NULL if the allocation failed. |
46 | ||
77f2ea2f | 47 | It also returns a <dma_handle> which may be cast to an unsigned integer the |
3a9ad0b4 | 48 | same width as the bus and given to the device as the DMA address base of |
77f2ea2f BH |
49 | the region. |
50 | ||
1da177e4 LT |
51 | Note: consistent memory can be expensive on some platforms, and the |
52 | minimum allocation length may be as big as a page, so you should | |
53 | consolidate your requests for consistent memory as much as possible. | |
54 | The simplest way to do that is to use the dma_pool calls (see below). | |
55 | ||
77f2ea2f | 56 | The flag parameter (dma_alloc_coherent() only) allows the caller to |
03158a70 | 57 | specify the ``GFP_`` flags (see kmalloc()) for the allocation (the |
a12e2c6c | 58 | implementation may choose to ignore flags that affect the location of |
f5a69f4c | 59 | the returned memory, like GFP_DMA). |
1da177e4 | 60 | |
03158a70 MCC |
61 | :: |
62 | ||
63 | void | |
64 | dma_free_coherent(struct device *dev, size_t size, void *cpu_addr, | |
65 | dma_addr_t dma_handle) | |
1da177e4 | 66 | |
77f2ea2f BH |
67 | Free a region of consistent memory you previously allocated. dev, |
68 | size and dma_handle must all be the same as those passed into | |
69 | dma_alloc_coherent(). cpu_addr must be the virtual address returned by | |
70 | the dma_alloc_coherent(). | |
1da177e4 | 71 | |
aa24886e DB |
72 | Note that unlike their sibling allocation calls, these routines |
73 | may only be called with IRQs enabled. | |
74 | ||
1da177e4 | 75 | |
77f2ea2f | 76 | Part Ib - Using small DMA-coherent buffers |
1da177e4 LT |
77 | ------------------------------------------ |
78 | ||
03158a70 | 79 | To get this part of the dma_API, you must #include <linux/dmapool.h> |
1da177e4 | 80 | |
77f2ea2f | 81 | Many drivers need lots of small DMA-coherent memory regions for DMA |
1da177e4 LT |
82 | descriptors or I/O buffers. Rather than allocating in units of a page |
83 | or more using dma_alloc_coherent(), you can use DMA pools. These work | |
77f2ea2f | 84 | much like a struct kmem_cache, except that they use the DMA-coherent allocator, |
1da177e4 | 85 | not __get_free_pages(). Also, they understand common hardware constraints |
a12e2c6c | 86 | for alignment, like queue heads needing to be aligned on N-byte boundaries. |
1da177e4 LT |
87 | |
88 | ||
03158a70 MCC |
89 | :: |
90 | ||
1da177e4 LT |
91 | struct dma_pool * |
92 | dma_pool_create(const char *name, struct device *dev, | |
93 | size_t size, size_t align, size_t alloc); | |
94 | ||
77f2ea2f | 95 | dma_pool_create() initializes a pool of DMA-coherent buffers |
1da177e4 LT |
96 | for use with a given device. It must be called in a context which |
97 | can sleep. | |
98 | ||
e18b890b | 99 | The "name" is for diagnostics (like a struct kmem_cache name); dev and size |
1da177e4 LT |
100 | are like what you'd pass to dma_alloc_coherent(). The device's hardware |
101 | alignment requirement for this type of data is "align" (which is expressed | |
102 | in bytes, and must be a power of two). If your device has no boundary | |
103 | crossing restrictions, pass 0 for alloc; passing 4096 says memory allocated | |
104 | from this pool must not cross 4KByte boundaries. | |
105 | ||
03158a70 | 106 | :: |
1da177e4 | 107 | |
03158a70 MCC |
108 | void * |
109 | dma_pool_zalloc(struct dma_pool *pool, gfp_t mem_flags, | |
110 | dma_addr_t *handle) | |
ad82362b SS |
111 | |
112 | Wraps dma_pool_alloc() and also zeroes the returned memory if the | |
113 | allocation attempt succeeded. | |
114 | ||
115 | ||
03158a70 MCC |
116 | :: |
117 | ||
118 | void * | |
119 | dma_pool_alloc(struct dma_pool *pool, gfp_t gfp_flags, | |
120 | dma_addr_t *dma_handle); | |
1da177e4 | 121 | |
77f2ea2f BH |
122 | This allocates memory from the pool; the returned memory will meet the |
123 | size and alignment requirements specified at creation time. Pass | |
124 | GFP_ATOMIC to prevent blocking, or if it's permitted (not | |
125 | in_interrupt, not holding SMP locks), pass GFP_KERNEL to allow | |
126 | blocking. Like dma_alloc_coherent(), this returns two values: an | |
f311a724 | 127 | address usable by the CPU, and the DMA address usable by the pool's |
77f2ea2f | 128 | device. |
1da177e4 | 129 | |
03158a70 | 130 | :: |
1da177e4 | 131 | |
03158a70 MCC |
132 | void |
133 | dma_pool_free(struct dma_pool *pool, void *vaddr, | |
134 | dma_addr_t addr); | |
1da177e4 | 135 | |
1da177e4 | 136 | This puts memory back into the pool. The pool is what was passed to |
f311a724 | 137 | dma_pool_alloc(); the CPU (vaddr) and DMA addresses are what |
1da177e4 LT |
138 | were returned when that routine allocated the memory being freed. |
139 | ||
03158a70 | 140 | :: |
1da177e4 | 141 | |
03158a70 MCC |
142 | void |
143 | dma_pool_destroy(struct dma_pool *pool); | |
1da177e4 | 144 | |
77f2ea2f | 145 | dma_pool_destroy() frees the resources of the pool. It must be |
1da177e4 LT |
146 | called in a context which can sleep. Make sure you've freed all allocated |
147 | memory back to the pool before you destroy it. | |
148 | ||
149 | ||
150 | Part Ic - DMA addressing limitations | |
151 | ------------------------------------ | |
152 | ||
03158a70 MCC |
153 | :: |
154 | ||
155 | int | |
156 | dma_set_mask_and_coherent(struct device *dev, u64 mask) | |
4aa806b7 RK |
157 | |
158 | Checks to see if the mask is possible and updates the device | |
159 | streaming and coherent DMA mask parameters if it is. | |
160 | ||
161 | Returns: 0 if successful and a negative error if not. | |
162 | ||
03158a70 MCC |
163 | :: |
164 | ||
165 | int | |
166 | dma_set_mask(struct device *dev, u64 mask) | |
1da177e4 LT |
167 | |
168 | Checks to see if the mask is possible and updates the device | |
169 | parameters if it is. | |
170 | ||
171 | Returns: 0 if successful and a negative error if not. | |
172 | ||
03158a70 MCC |
173 | :: |
174 | ||
175 | int | |
176 | dma_set_coherent_mask(struct device *dev, u64 mask) | |
6a1961f4 FT |
177 | |
178 | Checks to see if the mask is possible and updates the device | |
179 | parameters if it is. | |
180 | ||
181 | Returns: 0 if successful and a negative error if not. | |
182 | ||
03158a70 MCC |
183 | :: |
184 | ||
185 | u64 | |
186 | dma_get_required_mask(struct device *dev) | |
1da177e4 | 187 | |
175add19 JK |
188 | This API returns the mask that the platform requires to |
189 | operate efficiently. Usually this means the returned mask | |
1da177e4 LT |
190 | is the minimum required to cover all of memory. Examining the |
191 | required mask gives drivers with variable descriptor sizes the | |
192 | opportunity to use smaller descriptors as necessary. | |
193 | ||
194 | Requesting the required mask does not alter the current mask. If you | |
175add19 JK |
195 | wish to take advantage of it, you should issue a dma_set_mask() |
196 | call to set the mask to the value returned. | |
1da177e4 | 197 | |
133d624b JR |
198 | :: |
199 | ||
200 | size_t | |
99d2b938 | 201 | dma_max_mapping_size(struct device *dev); |
133d624b JR |
202 | |
203 | Returns the maximum size of a mapping for the device. The size parameter | |
204 | of the mapping functions like dma_map_single(), dma_map_page() and | |
205 | others should not be larger than the returned value. | |
1da177e4 | 206 | |
6ba99411 YS |
207 | :: |
208 | ||
209 | unsigned long | |
210 | dma_get_merge_boundary(struct device *dev); | |
211 | ||
212 | Returns the DMA merge boundary. If the device cannot merge any the DMA address | |
213 | segments, the function returns 0. | |
214 | ||
1da177e4 LT |
215 | Part Id - Streaming DMA mappings |
216 | -------------------------------- | |
217 | ||
03158a70 MCC |
218 | :: |
219 | ||
220 | dma_addr_t | |
221 | dma_map_single(struct device *dev, void *cpu_addr, size_t size, | |
222 | enum dma_data_direction direction) | |
1da177e4 LT |
223 | |
224 | Maps a piece of processor virtual memory so it can be accessed by the | |
3a9ad0b4 | 225 | device and returns the DMA address of the memory. |
1da177e4 | 226 | |
77f2ea2f | 227 | The direction for both APIs may be converted freely by casting. |
03158a70 | 228 | However the dma_API uses a strongly typed enumerator for its |
1da177e4 LT |
229 | direction: |
230 | ||
03158a70 | 231 | ======================= ============================================= |
f5a69f4c FT |
232 | DMA_NONE no direction (used for debugging) |
233 | DMA_TO_DEVICE data is going from the memory to the device | |
234 | DMA_FROM_DEVICE data is coming from the device to the memory | |
235 | DMA_BIDIRECTIONAL direction isn't known | |
03158a70 MCC |
236 | ======================= ============================================= |
237 | ||
238 | .. note:: | |
239 | ||
240 | Not all memory regions in a machine can be mapped by this API. | |
241 | Further, contiguous kernel virtual space may not be contiguous as | |
242 | physical memory. Since this API does not provide any scatter/gather | |
243 | capability, it will fail if the user tries to map a non-physically | |
244 | contiguous piece of memory. For this reason, memory to be mapped by | |
245 | this API should be obtained from sources which guarantee it to be | |
246 | physically contiguous (like kmalloc). | |
247 | ||
248 | Further, the DMA address of the memory must be within the | |
249 | dma_mask of the device (the dma_mask is a bit mask of the | |
250 | addressable region for the device, i.e., if the DMA address of | |
251 | the memory ANDed with the dma_mask is still equal to the DMA | |
252 | address, then the device can perform DMA to the memory). To | |
253 | ensure that the memory allocated by kmalloc is within the dma_mask, | |
254 | the driver may specify various platform-dependent flags to restrict | |
255 | the DMA address range of the allocation (e.g., on x86, GFP_DMA | |
256 | guarantees to be within the first 16MB of available DMA addresses, | |
257 | as required by ISA devices). | |
258 | ||
259 | Note also that the above constraints on physical contiguity and | |
260 | dma_mask may not apply if the platform has an IOMMU (a device which | |
261 | maps an I/O DMA address to a physical memory address). However, to be | |
262 | portable, device driver writers may *not* assume that such an IOMMU | |
263 | exists. | |
264 | ||
265 | .. warning:: | |
266 | ||
267 | Memory coherency operates at a granularity called the cache | |
268 | line width. In order for memory mapped by this API to operate | |
269 | correctly, the mapped region must begin exactly on a cache line | |
270 | boundary and end exactly on one (to prevent two separately mapped | |
271 | regions from sharing a single cache line). Since the cache line size | |
272 | may not be known at compile time, the API will not enforce this | |
273 | requirement. Therefore, it is recommended that driver writers who | |
274 | don't take special care to determine the cache line size at run time | |
275 | only map virtual regions that begin and end on page boundaries (which | |
276 | are guaranteed also to be cache line boundaries). | |
277 | ||
278 | DMA_TO_DEVICE synchronisation must be done after the last modification | |
279 | of the memory region by the software and before it is handed off to | |
280 | the device. Once this primitive is used, memory covered by this | |
281 | primitive should be treated as read-only by the device. If the device | |
282 | may write to it at any point, it should be DMA_BIDIRECTIONAL (see | |
283 | below). | |
284 | ||
285 | DMA_FROM_DEVICE synchronisation must be done before the driver | |
286 | accesses data that may be changed by the device. This memory should | |
287 | be treated as read-only by the driver. If the driver needs to write | |
288 | to it at any point, it should be DMA_BIDIRECTIONAL (see below). | |
289 | ||
290 | DMA_BIDIRECTIONAL requires special handling: it means that the driver | |
291 | isn't sure if the memory was modified before being handed off to the | |
292 | device and also isn't sure if the device will also modify it. Thus, | |
293 | you must always sync bidirectional memory twice: once before the | |
294 | memory is handed off to the device (to make sure all memory changes | |
295 | are flushed from the processor) and once before the data may be | |
296 | accessed after being used by the device (to make sure any processor | |
297 | cache lines are updated with data that the device may have changed). | |
298 | ||
299 | :: | |
1da177e4 | 300 | |
03158a70 MCC |
301 | void |
302 | dma_unmap_single(struct device *dev, dma_addr_t dma_addr, size_t size, | |
303 | enum dma_data_direction direction) | |
1da177e4 LT |
304 | |
305 | Unmaps the region previously mapped. All the parameters passed in | |
306 | must be identical to those passed in (and returned) by the mapping | |
307 | API. | |
308 | ||
03158a70 MCC |
309 | :: |
310 | ||
311 | dma_addr_t | |
312 | dma_map_page(struct device *dev, struct page *page, | |
313 | unsigned long offset, size_t size, | |
314 | enum dma_data_direction direction) | |
315 | ||
316 | void | |
317 | dma_unmap_page(struct device *dev, dma_addr_t dma_address, size_t size, | |
318 | enum dma_data_direction direction) | |
1da177e4 LT |
319 | |
320 | API for mapping and unmapping for pages. All the notes and warnings | |
321 | for the other mapping APIs apply here. Also, although the <offset> | |
322 | and <size> parameters are provided to do partial page mapping, it is | |
323 | recommended that you never use these unless you really know what the | |
324 | cache width is. | |
325 | ||
03158a70 | 326 | :: |
6f3d8796 | 327 | |
03158a70 MCC |
328 | dma_addr_t |
329 | dma_map_resource(struct device *dev, phys_addr_t phys_addr, size_t size, | |
330 | enum dma_data_direction dir, unsigned long attrs) | |
331 | ||
332 | void | |
333 | dma_unmap_resource(struct device *dev, dma_addr_t addr, size_t size, | |
334 | enum dma_data_direction dir, unsigned long attrs) | |
6f3d8796 NS |
335 | |
336 | API for mapping and unmapping for MMIO resources. All the notes and | |
337 | warnings for the other mapping APIs apply here. The API should only be | |
338 | used to map device MMIO resources, mapping of RAM is not permitted. | |
339 | ||
03158a70 MCC |
340 | :: |
341 | ||
342 | int | |
343 | dma_mapping_error(struct device *dev, dma_addr_t dma_addr) | |
1da177e4 | 344 | |
6f3d8796 NS |
345 | In some circumstances dma_map_single(), dma_map_page() and dma_map_resource() |
346 | will fail to create a mapping. A driver can check for these errors by testing | |
347 | the returned DMA address with dma_mapping_error(). A non-zero return value | |
348 | means the mapping could not be created and the driver should take appropriate | |
349 | action (e.g. reduce current DMA mapping usage or delay and try again later). | |
1da177e4 | 350 | |
03158a70 MCC |
351 | :: |
352 | ||
21440d31 DB |
353 | int |
354 | dma_map_sg(struct device *dev, struct scatterlist *sg, | |
03158a70 | 355 | int nents, enum dma_data_direction direction) |
1da177e4 | 356 | |
3a9ad0b4 | 357 | Returns: the number of DMA address segments mapped (this may be shorter |
1d678f36 FT |
358 | than <nents> passed in if some elements of the scatter/gather list are |
359 | physically or virtually adjacent and an IOMMU maps them with a single | |
360 | entry). | |
1da177e4 LT |
361 | |
362 | Please note that the sg cannot be mapped again if it has been mapped once. | |
363 | The mapping process is allowed to destroy information in the sg. | |
364 | ||
77f2ea2f | 365 | As with the other mapping interfaces, dma_map_sg() can fail. When it |
1da177e4 LT |
366 | does, 0 is returned and a driver must take appropriate action. It is |
367 | critical that the driver do something, in the case of a block driver | |
368 | aborting the request or even oopsing is better than doing nothing and | |
369 | corrupting the filesystem. | |
370 | ||
03158a70 | 371 | With scatterlists, you use the resulting mapping like this:: |
21440d31 DB |
372 | |
373 | int i, count = dma_map_sg(dev, sglist, nents, direction); | |
374 | struct scatterlist *sg; | |
375 | ||
79eb0145 | 376 | for_each_sg(sglist, sg, count, i) { |
21440d31 DB |
377 | hw_address[i] = sg_dma_address(sg); |
378 | hw_len[i] = sg_dma_len(sg); | |
379 | } | |
380 | ||
381 | where nents is the number of entries in the sglist. | |
382 | ||
383 | The implementation is free to merge several consecutive sglist entries | |
384 | into one (e.g. with an IOMMU, or if several pages just happen to be | |
385 | physically contiguous) and returns the actual number of sg entries it | |
386 | mapped them to. On failure 0, is returned. | |
387 | ||
388 | Then you should loop count times (note: this can be less than nents times) | |
389 | and use sg_dma_address() and sg_dma_len() macros where you previously | |
390 | accessed sg->address and sg->length as shown above. | |
391 | ||
03158a70 MCC |
392 | :: |
393 | ||
21440d31 DB |
394 | void |
395 | dma_unmap_sg(struct device *dev, struct scatterlist *sg, | |
03158a70 | 396 | int nents, enum dma_data_direction direction) |
1da177e4 | 397 | |
a12e2c6c | 398 | Unmap the previously mapped scatter/gather list. All the parameters |
1da177e4 LT |
399 | must be the same as those and passed in to the scatter/gather mapping |
400 | API. | |
401 | ||
402 | Note: <nents> must be the number you passed in, *not* the number of | |
3a9ad0b4 | 403 | DMA address entries returned. |
1da177e4 | 404 | |
03158a70 MCC |
405 | :: |
406 | ||
407 | void | |
408 | dma_sync_single_for_cpu(struct device *dev, dma_addr_t dma_handle, | |
409 | size_t size, | |
410 | enum dma_data_direction direction) | |
411 | ||
412 | void | |
413 | dma_sync_single_for_device(struct device *dev, dma_addr_t dma_handle, | |
414 | size_t size, | |
415 | enum dma_data_direction direction) | |
416 | ||
417 | void | |
418 | dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg, | |
419 | int nents, | |
420 | enum dma_data_direction direction) | |
421 | ||
422 | void | |
423 | dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg, | |
424 | int nents, | |
425 | enum dma_data_direction direction) | |
9705ef7e | 426 | |
f311a724 | 427 | Synchronise a single contiguous or scatter/gather mapping for the CPU |
9705ef7e FT |
428 | and device. With the sync_sg API, all the parameters must be the same |
429 | as those passed into the single mapping API. With the sync_single API, | |
430 | you can use dma_handle and size parameters that aren't identical to | |
431 | those passed into the single mapping API to do a partial sync. | |
432 | ||
9705ef7e | 433 | |
03158a70 MCC |
434 | .. note:: |
435 | ||
436 | You must do this: | |
437 | ||
438 | - Before reading values that have been written by DMA from the device | |
439 | (use the DMA_FROM_DEVICE direction) | |
440 | - After writing values that will be written to the device using DMA | |
441 | (use the DMA_TO_DEVICE) direction | |
442 | - before *and* after handing memory to the device if the memory is | |
443 | DMA_BIDIRECTIONAL | |
9705ef7e FT |
444 | |
445 | See also dma_map_single(). | |
446 | ||
03158a70 MCC |
447 | :: |
448 | ||
449 | dma_addr_t | |
450 | dma_map_single_attrs(struct device *dev, void *cpu_addr, size_t size, | |
451 | enum dma_data_direction dir, | |
452 | unsigned long attrs) | |
a75b0a2f | 453 | |
03158a70 MCC |
454 | void |
455 | dma_unmap_single_attrs(struct device *dev, dma_addr_t dma_addr, | |
456 | size_t size, enum dma_data_direction dir, | |
457 | unsigned long attrs) | |
a75b0a2f | 458 | |
03158a70 MCC |
459 | int |
460 | dma_map_sg_attrs(struct device *dev, struct scatterlist *sgl, | |
461 | int nents, enum dma_data_direction dir, | |
462 | unsigned long attrs) | |
a75b0a2f | 463 | |
03158a70 MCC |
464 | void |
465 | dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sgl, | |
466 | int nents, enum dma_data_direction dir, | |
467 | unsigned long attrs) | |
a75b0a2f AK |
468 | |
469 | The four functions above are just like the counterpart functions | |
470 | without the _attrs suffixes, except that they pass an optional | |
00085f1e | 471 | dma_attrs. |
a75b0a2f | 472 | |
77f2ea2f | 473 | The interpretation of DMA attributes is architecture-specific, and |
a75b0a2f AK |
474 | each attribute should be documented in Documentation/DMA-attributes.txt. |
475 | ||
00085f1e KK |
476 | If dma_attrs are 0, the semantics of each of these functions |
477 | is identical to those of the corresponding function | |
a75b0a2f AK |
478 | without the _attrs suffix. As a result dma_map_single_attrs() |
479 | can generally replace dma_map_single(), etc. | |
480 | ||
03158a70 | 481 | As an example of the use of the ``*_attrs`` functions, here's how |
a75b0a2f | 482 | you could pass an attribute DMA_ATTR_FOO when mapping memory |
03158a70 | 483 | for DMA:: |
a75b0a2f | 484 | |
03158a70 MCC |
485 | #include <linux/dma-mapping.h> |
486 | /* DMA_ATTR_FOO should be defined in linux/dma-mapping.h and | |
487 | * documented in Documentation/DMA-attributes.txt */ | |
488 | ... | |
a75b0a2f | 489 | |
03158a70 MCC |
490 | unsigned long attr; |
491 | attr |= DMA_ATTR_FOO; | |
492 | .... | |
493 | n = dma_map_sg_attrs(dev, sg, nents, DMA_TO_DEVICE, attr); | |
494 | .... | |
a75b0a2f AK |
495 | |
496 | Architectures that care about DMA_ATTR_FOO would check for its | |
497 | presence in their implementations of the mapping and unmapping | |
03158a70 MCC |
498 | routines, e.g.::: |
499 | ||
500 | void whizco_dma_map_sg_attrs(struct device *dev, dma_addr_t dma_addr, | |
501 | size_t size, enum dma_data_direction dir, | |
502 | unsigned long attrs) | |
503 | { | |
504 | .... | |
505 | if (attrs & DMA_ATTR_FOO) | |
506 | /* twizzle the frobnozzle */ | |
507 | .... | |
508 | } | |
a75b0a2f | 509 | |
1da177e4 | 510 | |
03158a70 MCC |
511 | Part II - Advanced dma usage |
512 | ---------------------------- | |
1da177e4 | 513 | |
f5a69f4c FT |
514 | Warning: These pieces of the DMA API should not be used in the |
515 | majority of cases, since they cater for unlikely corner cases that | |
516 | don't belong in usual drivers. | |
1da177e4 LT |
517 | |
518 | If you don't understand how cache line coherency works between a | |
519 | processor and an I/O device, you should not be using this part of the | |
520 | API at all. | |
521 | ||
03158a70 MCC |
522 | :: |
523 | ||
524 | void * | |
2fd523c5 CH |
525 | dma_alloc_attrs(struct device *dev, size_t size, dma_addr_t *dma_handle, |
526 | gfp_t flag, unsigned long attrs) | |
1da177e4 | 527 | |
2fd523c5 CH |
528 | Identical to dma_alloc_coherent() except that when the |
529 | DMA_ATTR_NON_CONSISTENT flags is passed in the attrs argument, the | |
530 | platform will choose to return either consistent or non-consistent memory | |
531 | as it sees fit. By using this API, you are guaranteeing to the platform | |
532 | that you have all the correct and necessary sync points for this memory | |
533 | in the driver should it choose to return non-consistent memory. | |
1da177e4 LT |
534 | |
535 | Note: where the platform can return consistent memory, it will | |
536 | guarantee that the sync points become nops. | |
537 | ||
538 | Warning: Handling non-consistent memory is a real pain. You should | |
77f2ea2f | 539 | only use this API if you positively know your driver will be |
1da177e4 LT |
540 | required to work on one of the rare (usually non-PCI) architectures |
541 | that simply cannot make consistent memory. | |
542 | ||
03158a70 MCC |
543 | :: |
544 | ||
545 | void | |
2fd523c5 CH |
546 | dma_free_attrs(struct device *dev, size_t size, void *cpu_addr, |
547 | dma_addr_t dma_handle, unsigned long attrs) | |
1da177e4 | 548 | |
31f43330 CL |
549 | Free memory allocated by the dma_alloc_attrs(). All common |
550 | parameters must be identical to those otherwise passed to dma_free_coherent, | |
2fd523c5 CH |
551 | and the attrs argument must be identical to the attrs passed to |
552 | dma_alloc_attrs(). | |
1da177e4 | 553 | |
03158a70 MCC |
554 | :: |
555 | ||
556 | int | |
557 | dma_get_cache_alignment(void) | |
1da177e4 | 558 | |
a12e2c6c | 559 | Returns the processor cache alignment. This is the absolute minimum |
1da177e4 LT |
560 | alignment *and* width that you must observe when either mapping |
561 | memory or doing partial flushes. | |
562 | ||
03158a70 | 563 | .. note:: |
1da177e4 | 564 | |
03158a70 MCC |
565 | This API may return a number *larger* than the actual cache |
566 | line, but it will guarantee that one or more cache lines fit exactly | |
567 | into the width returned by this call. It will also always be a power | |
568 | of two for easy alignment. | |
569 | ||
570 | :: | |
571 | ||
572 | void | |
573 | dma_cache_sync(struct device *dev, void *vaddr, size_t size, | |
574 | enum dma_data_direction direction) | |
1da177e4 | 575 | |
2fd523c5 CH |
576 | Do a partial sync of memory that was allocated by dma_alloc_attrs() with |
577 | the DMA_ATTR_NON_CONSISTENT flag starting at virtual address vaddr and | |
1da177e4 LT |
578 | continuing on for size. Again, you *must* observe the cache line |
579 | boundaries when doing this. | |
580 | ||
03158a70 MCC |
581 | :: |
582 | ||
583 | int | |
584 | dma_declare_coherent_memory(struct device *dev, phys_addr_t phys_addr, | |
82c5de0a | 585 | dma_addr_t device_addr, size_t size); |
1da177e4 | 586 | |
77f2ea2f | 587 | Declare region of memory to be handed out by dma_alloc_coherent() when |
1da177e4 LT |
588 | it's asked for coherent memory for this device. |
589 | ||
f311a724 BH |
590 | phys_addr is the CPU physical address to which the memory is currently |
591 | assigned (this will be ioremapped so the CPU can access the region). | |
1da177e4 | 592 | |
3a9ad0b4 | 593 | device_addr is the DMA address the device needs to be programmed |
88a984ba | 594 | with to actually address this memory (this will be handed out as the |
a12e2c6c | 595 | dma_addr_t in dma_alloc_coherent()). |
1da177e4 LT |
596 | |
597 | size is the size of the area (must be multiples of PAGE_SIZE). | |
598 | ||
2436bdcd | 599 | As a simplification for the platforms, only *one* such region of |
1da177e4 LT |
600 | memory may be declared per device. |
601 | ||
602 | For reasons of efficiency, most platforms choose to track the declared | |
603 | region only at the granularity of a page. For smaller allocations, | |
604 | you should use the dma_pool() API. | |
605 | ||
187f9c3f JR |
606 | Part III - Debug drivers use of the DMA-API |
607 | ------------------------------------------- | |
608 | ||
77f2ea2f | 609 | The DMA-API as described above has some constraints. DMA addresses must be |
187f9c3f JR |
610 | released with the corresponding function with the same size for example. With |
611 | the advent of hardware IOMMUs it becomes more and more important that drivers | |
612 | do not violate those constraints. In the worst case such a violation can | |
613 | result in data corruption up to destroyed filesystems. | |
614 | ||
615 | To debug drivers and find bugs in the usage of the DMA-API checking code can | |
616 | be compiled into the kernel which will tell the developer about those | |
617 | violations. If your architecture supports it you can select the "Enable | |
618 | debugging of DMA-API usage" option in your kernel configuration. Enabling this | |
619 | option has a performance impact. Do not enable it in production kernels. | |
620 | ||
621 | If you boot the resulting kernel will contain code which does some bookkeeping | |
622 | about what DMA memory was allocated for which device. If this code detects an | |
623 | error it prints a warning message with some details into your kernel log. An | |
03158a70 MCC |
624 | example warning message may look like this:: |
625 | ||
626 | WARNING: at /data2/repos/linux-2.6-iommu/lib/dma-debug.c:448 | |
627 | check_unmap+0x203/0x490() | |
628 | Hardware name: | |
629 | forcedeth 0000:00:08.0: DMA-API: device driver frees DMA memory with wrong | |
630 | function [device address=0x00000000640444be] [size=66 bytes] [mapped as | |
631 | single] [unmapped as page] | |
632 | Modules linked in: nfsd exportfs bridge stp llc r8169 | |
633 | Pid: 0, comm: swapper Tainted: G W 2.6.28-dmatest-09289-g8bb99c0 #1 | |
634 | Call Trace: | |
635 | <IRQ> [<ffffffff80240b22>] warn_slowpath+0xf2/0x130 | |
636 | [<ffffffff80647b70>] _spin_unlock+0x10/0x30 | |
637 | [<ffffffff80537e75>] usb_hcd_link_urb_to_ep+0x75/0xc0 | |
638 | [<ffffffff80647c22>] _spin_unlock_irqrestore+0x12/0x40 | |
639 | [<ffffffff8055347f>] ohci_urb_enqueue+0x19f/0x7c0 | |
640 | [<ffffffff80252f96>] queue_work+0x56/0x60 | |
641 | [<ffffffff80237e10>] enqueue_task_fair+0x20/0x50 | |
642 | [<ffffffff80539279>] usb_hcd_submit_urb+0x379/0xbc0 | |
643 | [<ffffffff803b78c3>] cpumask_next_and+0x23/0x40 | |
644 | [<ffffffff80235177>] find_busiest_group+0x207/0x8a0 | |
645 | [<ffffffff8064784f>] _spin_lock_irqsave+0x1f/0x50 | |
646 | [<ffffffff803c7ea3>] check_unmap+0x203/0x490 | |
647 | [<ffffffff803c8259>] debug_dma_unmap_page+0x49/0x50 | |
648 | [<ffffffff80485f26>] nv_tx_done_optimized+0xc6/0x2c0 | |
649 | [<ffffffff80486c13>] nv_nic_irq_optimized+0x73/0x2b0 | |
650 | [<ffffffff8026df84>] handle_IRQ_event+0x34/0x70 | |
651 | [<ffffffff8026ffe9>] handle_edge_irq+0xc9/0x150 | |
652 | [<ffffffff8020e3ab>] do_IRQ+0xcb/0x1c0 | |
653 | [<ffffffff8020c093>] ret_from_intr+0x0/0xa | |
654 | <EOI> <4>---[ end trace f6435a98e2a38c0e ]--- | |
187f9c3f JR |
655 | |
656 | The driver developer can find the driver and the device including a stacktrace | |
657 | of the DMA-API call which caused this warning. | |
658 | ||
659 | Per default only the first error will result in a warning message. All other | |
660 | errors will only silently counted. This limitation exist to prevent the code | |
661 | from flooding your kernel log. To support debugging a device driver this can | |
662 | be disabled via debugfs. See the debugfs interface documentation below for | |
663 | details. | |
664 | ||
665 | The debugfs directory for the DMA-API debugging code is called dma-api/. In | |
666 | this directory the following files can currently be found: | |
667 | ||
03158a70 MCC |
668 | =============================== =============================================== |
669 | dma-api/all_errors This file contains a numeric value. If this | |
187f9c3f JR |
670 | value is not equal to zero the debugging code |
671 | will print a warning for every error it finds | |
19f59460 ML |
672 | into the kernel log. Be careful with this |
673 | option, as it can easily flood your logs. | |
187f9c3f | 674 | |
03158a70 | 675 | dma-api/disabled This read-only file contains the character 'Y' |
187f9c3f JR |
676 | if the debugging code is disabled. This can |
677 | happen when it runs out of memory or if it was | |
678 | disabled at boot time | |
679 | ||
0a3b192c CL |
680 | dma-api/dump This read-only file contains current DMA |
681 | mappings. | |
682 | ||
03158a70 | 683 | dma-api/error_count This file is read-only and shows the total |
187f9c3f JR |
684 | numbers of errors found. |
685 | ||
03158a70 | 686 | dma-api/num_errors The number in this file shows how many |
187f9c3f JR |
687 | warnings will be printed to the kernel log |
688 | before it stops. This number is initialized to | |
689 | one at system boot and be set by writing into | |
690 | this file | |
691 | ||
03158a70 | 692 | dma-api/min_free_entries This read-only file can be read to get the |
187f9c3f JR |
693 | minimum number of free dma_debug_entries the |
694 | allocator has ever seen. If this value goes | |
2b9d9ac0 RM |
695 | down to zero the code will attempt to increase |
696 | nr_total_entries to compensate. | |
187f9c3f | 697 | |
03158a70 | 698 | dma-api/num_free_entries The current number of free dma_debug_entries |
187f9c3f JR |
699 | in the allocator. |
700 | ||
9f191555 RM |
701 | dma-api/nr_total_entries The total number of dma_debug_entries in the |
702 | allocator, both free and used. | |
703 | ||
31f43330 | 704 | dma-api/driver_filter You can write a name of a driver into this file |
016ea687 JR |
705 | to limit the debug output to requests from that |
706 | particular driver. Write an empty string to | |
707 | that file to disable the filter and see | |
708 | all errors again. | |
03158a70 | 709 | =============================== =============================================== |
016ea687 | 710 | |
187f9c3f JR |
711 | If you have this code compiled into your kernel it will be enabled by default. |
712 | If you want to boot without the bookkeeping anyway you can provide | |
713 | 'dma_debug=off' as a boot parameter. This will disable DMA-API debugging. | |
714 | Notice that you can not enable it again at runtime. You have to reboot to do | |
715 | so. | |
716 | ||
016ea687 JR |
717 | If you want to see debug messages only for a special device driver you can |
718 | specify the dma_debug_driver=<drivername> parameter. This will enable the | |
719 | driver filter at boot time. The debug code will only print errors for that | |
720 | driver afterwards. This filter can be disabled or changed later using debugfs. | |
721 | ||
187f9c3f | 722 | When the code disables itself at runtime this is most likely because it ran |
2b9d9ac0 RM |
723 | out of dma_debug_entries and was unable to allocate more on-demand. 65536 |
724 | entries are preallocated at boot - if this is too low for you boot with | |
ad78dee0 RM |
725 | 'dma_debug_entries=<your_desired_number>' to overwrite the default. Note |
726 | that the code allocates entries in batches, so the exact number of | |
727 | preallocated entries may be greater than the actual number requested. The | |
ceb51173 RM |
728 | code will print to the kernel log each time it has dynamically allocated |
729 | as many entries as were initially preallocated. This is to indicate that a | |
730 | larger preallocation size may be appropriate, or if it happens continually | |
731 | that a driver may be leaking mappings. | |
6c9c6d63 | 732 | |
03158a70 MCC |
733 | :: |
734 | ||
735 | void | |
736 | debug_dma_mapping_error(struct device *dev, dma_addr_t dma_addr); | |
6c9c6d63 SK |
737 | |
738 | dma-debug interface debug_dma_mapping_error() to debug drivers that fail | |
77f2ea2f | 739 | to check DMA mapping errors on addresses returned by dma_map_single() and |
6c9c6d63 SK |
740 | dma_map_page() interfaces. This interface clears a flag set by |
741 | debug_dma_map_page() to indicate that dma_mapping_error() has been called by | |
742 | the driver. When driver does unmap, debug_dma_unmap() checks the flag and if | |
743 | this flag is still set, prints warning message that includes call trace that | |
744 | leads up to the unmap. This interface can be called from dma_mapping_error() | |
77f2ea2f | 745 | routines to enable DMA mapping error check debugging. |