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1da177e4 LT |
1 | Dynamic DMA mapping using the generic device |
2 | ============================================ | |
3 | ||
4 | James E.J. Bottomley <James.Bottomley@HansenPartnership.com> | |
5 | ||
6 | This document describes the DMA API. For a more gentle introduction | |
77f2ea2f | 7 | of the API (and actual examples), see Documentation/DMA-API-HOWTO.txt. |
1da177e4 | 8 | |
77f2ea2f BH |
9 | This API is split into two pieces. Part I describes the basic API. |
10 | Part II describes extensions for supporting non-consistent memory | |
11 | machines. Unless you know that your driver absolutely has to support | |
12 | non-consistent platforms (this is usually only legacy platforms) you | |
13 | should only use the API described in part I. | |
1da177e4 | 14 | |
f5a69f4c | 15 | Part I - dma_ API |
1da177e4 LT |
16 | ------------------------------------- |
17 | ||
77f2ea2f BH |
18 | To get the dma_ API, you must #include <linux/dma-mapping.h>. This |
19 | provides dma_addr_t and the interfaces described below. | |
1da177e4 | 20 | |
3a9ad0b4 YL |
21 | A dma_addr_t can hold any valid DMA address for the platform. It can be |
22 | given to a device to use as a DMA source or target. A CPU cannot reference | |
23 | a dma_addr_t directly because there may be translation between its physical | |
24 | address space and the DMA address space. | |
1da177e4 | 25 | |
77f2ea2f | 26 | Part Ia - Using large DMA-coherent buffers |
1da177e4 LT |
27 | ------------------------------------------ |
28 | ||
29 | void * | |
30 | dma_alloc_coherent(struct device *dev, size_t size, | |
a12e2c6c | 31 | dma_addr_t *dma_handle, gfp_t flag) |
1da177e4 LT |
32 | |
33 | Consistent memory is memory for which a write by either the device or | |
34 | the processor can immediately be read by the processor or device | |
21440d31 DB |
35 | without having to worry about caching effects. (You may however need |
36 | to make sure to flush the processor's write buffers before telling | |
37 | devices to read that memory.) | |
1da177e4 LT |
38 | |
39 | This routine allocates a region of <size> bytes of consistent memory. | |
1da177e4 | 40 | |
77f2ea2f | 41 | It returns a pointer to the allocated region (in the processor's virtual |
1da177e4 LT |
42 | address space) or NULL if the allocation failed. |
43 | ||
77f2ea2f | 44 | It also returns a <dma_handle> which may be cast to an unsigned integer the |
3a9ad0b4 | 45 | same width as the bus and given to the device as the DMA address base of |
77f2ea2f BH |
46 | the region. |
47 | ||
1da177e4 LT |
48 | Note: consistent memory can be expensive on some platforms, and the |
49 | minimum allocation length may be as big as a page, so you should | |
50 | consolidate your requests for consistent memory as much as possible. | |
51 | The simplest way to do that is to use the dma_pool calls (see below). | |
52 | ||
77f2ea2f BH |
53 | The flag parameter (dma_alloc_coherent() only) allows the caller to |
54 | specify the GFP_ flags (see kmalloc()) for the allocation (the | |
a12e2c6c | 55 | implementation may choose to ignore flags that affect the location of |
f5a69f4c | 56 | the returned memory, like GFP_DMA). |
1da177e4 | 57 | |
842fa69f AM |
58 | void * |
59 | dma_zalloc_coherent(struct device *dev, size_t size, | |
60 | dma_addr_t *dma_handle, gfp_t flag) | |
61 | ||
62 | Wraps dma_alloc_coherent() and also zeroes the returned memory if the | |
63 | allocation attempt succeeded. | |
64 | ||
1da177e4 | 65 | void |
a12e2c6c | 66 | dma_free_coherent(struct device *dev, size_t size, void *cpu_addr, |
1da177e4 | 67 | dma_addr_t dma_handle) |
1da177e4 | 68 | |
77f2ea2f BH |
69 | Free a region of consistent memory you previously allocated. dev, |
70 | size and dma_handle must all be the same as those passed into | |
71 | dma_alloc_coherent(). cpu_addr must be the virtual address returned by | |
72 | the dma_alloc_coherent(). | |
1da177e4 | 73 | |
aa24886e DB |
74 | Note that unlike their sibling allocation calls, these routines |
75 | may only be called with IRQs enabled. | |
76 | ||
1da177e4 | 77 | |
77f2ea2f | 78 | Part Ib - Using small DMA-coherent buffers |
1da177e4 LT |
79 | ------------------------------------------ |
80 | ||
81 | To get this part of the dma_ API, you must #include <linux/dmapool.h> | |
82 | ||
77f2ea2f | 83 | Many drivers need lots of small DMA-coherent memory regions for DMA |
1da177e4 LT |
84 | descriptors or I/O buffers. Rather than allocating in units of a page |
85 | or more using dma_alloc_coherent(), you can use DMA pools. These work | |
77f2ea2f | 86 | much like a struct kmem_cache, except that they use the DMA-coherent allocator, |
1da177e4 | 87 | not __get_free_pages(). Also, they understand common hardware constraints |
a12e2c6c | 88 | for alignment, like queue heads needing to be aligned on N-byte boundaries. |
1da177e4 LT |
89 | |
90 | ||
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 | ||
106 | ||
ad82362b SS |
107 | void *dma_pool_zalloc(struct dma_pool *pool, gfp_t mem_flags, |
108 | dma_addr_t *handle) | |
109 | ||
110 | Wraps dma_pool_alloc() and also zeroes the returned memory if the | |
111 | allocation attempt succeeded. | |
112 | ||
113 | ||
a12e2c6c | 114 | void *dma_pool_alloc(struct dma_pool *pool, gfp_t gfp_flags, |
1da177e4 LT |
115 | dma_addr_t *dma_handle); |
116 | ||
77f2ea2f BH |
117 | This allocates memory from the pool; the returned memory will meet the |
118 | size and alignment requirements specified at creation time. Pass | |
119 | GFP_ATOMIC to prevent blocking, or if it's permitted (not | |
120 | in_interrupt, not holding SMP locks), pass GFP_KERNEL to allow | |
121 | blocking. Like dma_alloc_coherent(), this returns two values: an | |
f311a724 | 122 | address usable by the CPU, and the DMA address usable by the pool's |
77f2ea2f | 123 | device. |
1da177e4 LT |
124 | |
125 | ||
126 | void dma_pool_free(struct dma_pool *pool, void *vaddr, | |
127 | dma_addr_t addr); | |
128 | ||
1da177e4 | 129 | This puts memory back into the pool. The pool is what was passed to |
f311a724 | 130 | dma_pool_alloc(); the CPU (vaddr) and DMA addresses are what |
1da177e4 LT |
131 | were returned when that routine allocated the memory being freed. |
132 | ||
133 | ||
134 | void dma_pool_destroy(struct dma_pool *pool); | |
135 | ||
77f2ea2f | 136 | dma_pool_destroy() frees the resources of the pool. It must be |
1da177e4 LT |
137 | called in a context which can sleep. Make sure you've freed all allocated |
138 | memory back to the pool before you destroy it. | |
139 | ||
140 | ||
141 | Part Ic - DMA addressing limitations | |
142 | ------------------------------------ | |
143 | ||
4aa806b7 RK |
144 | int |
145 | dma_set_mask_and_coherent(struct device *dev, u64 mask) | |
146 | ||
147 | Checks to see if the mask is possible and updates the device | |
148 | streaming and coherent DMA mask parameters if it is. | |
149 | ||
150 | Returns: 0 if successful and a negative error if not. | |
151 | ||
1da177e4 LT |
152 | int |
153 | dma_set_mask(struct device *dev, u64 mask) | |
1da177e4 LT |
154 | |
155 | Checks to see if the mask is possible and updates the device | |
156 | parameters if it is. | |
157 | ||
158 | Returns: 0 if successful and a negative error if not. | |
159 | ||
6a1961f4 FT |
160 | int |
161 | dma_set_coherent_mask(struct device *dev, u64 mask) | |
6a1961f4 FT |
162 | |
163 | Checks to see if the mask is possible and updates the device | |
164 | parameters if it is. | |
165 | ||
166 | Returns: 0 if successful and a negative error if not. | |
167 | ||
1da177e4 LT |
168 | u64 |
169 | dma_get_required_mask(struct device *dev) | |
170 | ||
175add19 JK |
171 | This API returns the mask that the platform requires to |
172 | operate efficiently. Usually this means the returned mask | |
1da177e4 LT |
173 | is the minimum required to cover all of memory. Examining the |
174 | required mask gives drivers with variable descriptor sizes the | |
175 | opportunity to use smaller descriptors as necessary. | |
176 | ||
177 | Requesting the required mask does not alter the current mask. If you | |
175add19 JK |
178 | wish to take advantage of it, you should issue a dma_set_mask() |
179 | call to set the mask to the value returned. | |
1da177e4 LT |
180 | |
181 | ||
182 | Part Id - Streaming DMA mappings | |
183 | -------------------------------- | |
184 | ||
185 | dma_addr_t | |
186 | dma_map_single(struct device *dev, void *cpu_addr, size_t size, | |
187 | enum dma_data_direction direction) | |
1da177e4 LT |
188 | |
189 | Maps a piece of processor virtual memory so it can be accessed by the | |
3a9ad0b4 | 190 | device and returns the DMA address of the memory. |
1da177e4 | 191 | |
77f2ea2f | 192 | The direction for both APIs may be converted freely by casting. |
1da177e4 LT |
193 | However the dma_ API uses a strongly typed enumerator for its |
194 | direction: | |
195 | ||
f5a69f4c FT |
196 | DMA_NONE no direction (used for debugging) |
197 | DMA_TO_DEVICE data is going from the memory to the device | |
198 | DMA_FROM_DEVICE data is coming from the device to the memory | |
199 | DMA_BIDIRECTIONAL direction isn't known | |
1da177e4 | 200 | |
77f2ea2f BH |
201 | Notes: Not all memory regions in a machine can be mapped by this API. |
202 | Further, contiguous kernel virtual space may not be contiguous as | |
203 | physical memory. Since this API does not provide any scatter/gather | |
204 | capability, it will fail if the user tries to map a non-physically | |
205 | contiguous piece of memory. For this reason, memory to be mapped by | |
206 | this API should be obtained from sources which guarantee it to be | |
207 | physically contiguous (like kmalloc). | |
208 | ||
3a9ad0b4 | 209 | Further, the DMA address of the memory must be within the |
77f2ea2f | 210 | dma_mask of the device (the dma_mask is a bit mask of the |
3a9ad0b4 YL |
211 | addressable region for the device, i.e., if the DMA address of |
212 | the memory ANDed with the dma_mask is still equal to the DMA | |
77f2ea2f | 213 | address, then the device can perform DMA to the memory). To |
1da177e4 | 214 | ensure that the memory allocated by kmalloc is within the dma_mask, |
a12e2c6c | 215 | the driver may specify various platform-dependent flags to restrict |
3a9ad0b4 YL |
216 | the DMA address range of the allocation (e.g., on x86, GFP_DMA |
217 | guarantees to be within the first 16MB of available DMA addresses, | |
1da177e4 LT |
218 | as required by ISA devices). |
219 | ||
220 | Note also that the above constraints on physical contiguity and | |
221 | dma_mask may not apply if the platform has an IOMMU (a device which | |
3a9ad0b4 | 222 | maps an I/O DMA address to a physical memory address). However, to be |
77f2ea2f BH |
223 | portable, device driver writers may *not* assume that such an IOMMU |
224 | exists. | |
1da177e4 LT |
225 | |
226 | Warnings: Memory coherency operates at a granularity called the cache | |
227 | line width. In order for memory mapped by this API to operate | |
228 | correctly, the mapped region must begin exactly on a cache line | |
229 | boundary and end exactly on one (to prevent two separately mapped | |
230 | regions from sharing a single cache line). Since the cache line size | |
231 | may not be known at compile time, the API will not enforce this | |
232 | requirement. Therefore, it is recommended that driver writers who | |
233 | don't take special care to determine the cache line size at run time | |
234 | only map virtual regions that begin and end on page boundaries (which | |
235 | are guaranteed also to be cache line boundaries). | |
236 | ||
237 | DMA_TO_DEVICE synchronisation must be done after the last modification | |
238 | of the memory region by the software and before it is handed off to | |
000afe89 | 239 | the device. Once this primitive is used, memory covered by this |
a12e2c6c | 240 | primitive should be treated as read-only by the device. If the device |
1da177e4 LT |
241 | may write to it at any point, it should be DMA_BIDIRECTIONAL (see |
242 | below). | |
243 | ||
244 | DMA_FROM_DEVICE synchronisation must be done before the driver | |
245 | accesses data that may be changed by the device. This memory should | |
a12e2c6c | 246 | be treated as read-only by the driver. If the driver needs to write |
1da177e4 LT |
247 | to it at any point, it should be DMA_BIDIRECTIONAL (see below). |
248 | ||
249 | DMA_BIDIRECTIONAL requires special handling: it means that the driver | |
250 | isn't sure if the memory was modified before being handed off to the | |
251 | device and also isn't sure if the device will also modify it. Thus, | |
252 | you must always sync bidirectional memory twice: once before the | |
253 | memory is handed off to the device (to make sure all memory changes | |
254 | are flushed from the processor) and once before the data may be | |
255 | accessed after being used by the device (to make sure any processor | |
a12e2c6c | 256 | cache lines are updated with data that the device may have changed). |
1da177e4 LT |
257 | |
258 | void | |
259 | dma_unmap_single(struct device *dev, dma_addr_t dma_addr, size_t size, | |
260 | enum dma_data_direction direction) | |
1da177e4 LT |
261 | |
262 | Unmaps the region previously mapped. All the parameters passed in | |
263 | must be identical to those passed in (and returned) by the mapping | |
264 | API. | |
265 | ||
266 | dma_addr_t | |
267 | dma_map_page(struct device *dev, struct page *page, | |
268 | unsigned long offset, size_t size, | |
269 | enum dma_data_direction direction) | |
1da177e4 LT |
270 | void |
271 | dma_unmap_page(struct device *dev, dma_addr_t dma_address, size_t size, | |
272 | enum dma_data_direction direction) | |
1da177e4 LT |
273 | |
274 | API for mapping and unmapping for pages. All the notes and warnings | |
275 | for the other mapping APIs apply here. Also, although the <offset> | |
276 | and <size> parameters are provided to do partial page mapping, it is | |
277 | recommended that you never use these unless you really know what the | |
278 | cache width is. | |
279 | ||
6f3d8796 NS |
280 | dma_addr_t |
281 | dma_map_resource(struct device *dev, phys_addr_t phys_addr, size_t size, | |
282 | enum dma_data_direction dir, unsigned long attrs) | |
283 | ||
284 | void | |
285 | dma_unmap_resource(struct device *dev, dma_addr_t addr, size_t size, | |
286 | enum dma_data_direction dir, unsigned long attrs) | |
287 | ||
288 | API for mapping and unmapping for MMIO resources. All the notes and | |
289 | warnings for the other mapping APIs apply here. The API should only be | |
290 | used to map device MMIO resources, mapping of RAM is not permitted. | |
291 | ||
1da177e4 | 292 | int |
8d8bb39b | 293 | dma_mapping_error(struct device *dev, dma_addr_t dma_addr) |
1da177e4 | 294 | |
6f3d8796 NS |
295 | In some circumstances dma_map_single(), dma_map_page() and dma_map_resource() |
296 | will fail to create a mapping. A driver can check for these errors by testing | |
297 | the returned DMA address with dma_mapping_error(). A non-zero return value | |
298 | means the mapping could not be created and the driver should take appropriate | |
299 | action (e.g. reduce current DMA mapping usage or delay and try again later). | |
1da177e4 | 300 | |
21440d31 DB |
301 | int |
302 | dma_map_sg(struct device *dev, struct scatterlist *sg, | |
303 | int nents, enum dma_data_direction direction) | |
1da177e4 | 304 | |
3a9ad0b4 | 305 | Returns: the number of DMA address segments mapped (this may be shorter |
1d678f36 FT |
306 | than <nents> passed in if some elements of the scatter/gather list are |
307 | physically or virtually adjacent and an IOMMU maps them with a single | |
308 | entry). | |
1da177e4 LT |
309 | |
310 | Please note that the sg cannot be mapped again if it has been mapped once. | |
311 | The mapping process is allowed to destroy information in the sg. | |
312 | ||
77f2ea2f | 313 | As with the other mapping interfaces, dma_map_sg() can fail. When it |
1da177e4 LT |
314 | does, 0 is returned and a driver must take appropriate action. It is |
315 | critical that the driver do something, in the case of a block driver | |
316 | aborting the request or even oopsing is better than doing nothing and | |
317 | corrupting the filesystem. | |
318 | ||
21440d31 DB |
319 | With scatterlists, you use the resulting mapping like this: |
320 | ||
321 | int i, count = dma_map_sg(dev, sglist, nents, direction); | |
322 | struct scatterlist *sg; | |
323 | ||
79eb0145 | 324 | for_each_sg(sglist, sg, count, i) { |
21440d31 DB |
325 | hw_address[i] = sg_dma_address(sg); |
326 | hw_len[i] = sg_dma_len(sg); | |
327 | } | |
328 | ||
329 | where nents is the number of entries in the sglist. | |
330 | ||
331 | The implementation is free to merge several consecutive sglist entries | |
332 | into one (e.g. with an IOMMU, or if several pages just happen to be | |
333 | physically contiguous) and returns the actual number of sg entries it | |
334 | mapped them to. On failure 0, is returned. | |
335 | ||
336 | Then you should loop count times (note: this can be less than nents times) | |
337 | and use sg_dma_address() and sg_dma_len() macros where you previously | |
338 | accessed sg->address and sg->length as shown above. | |
339 | ||
340 | void | |
341 | dma_unmap_sg(struct device *dev, struct scatterlist *sg, | |
7bc590b2 | 342 | int nents, enum dma_data_direction direction) |
1da177e4 | 343 | |
a12e2c6c | 344 | Unmap the previously mapped scatter/gather list. All the parameters |
1da177e4 LT |
345 | must be the same as those and passed in to the scatter/gather mapping |
346 | API. | |
347 | ||
348 | Note: <nents> must be the number you passed in, *not* the number of | |
3a9ad0b4 | 349 | DMA address entries returned. |
1da177e4 | 350 | |
9705ef7e FT |
351 | void |
352 | dma_sync_single_for_cpu(struct device *dev, dma_addr_t dma_handle, size_t size, | |
353 | enum dma_data_direction direction) | |
354 | void | |
9705ef7e FT |
355 | dma_sync_single_for_device(struct device *dev, dma_addr_t dma_handle, size_t size, |
356 | enum dma_data_direction direction) | |
357 | void | |
7bc590b2 | 358 | dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg, int nents, |
9705ef7e FT |
359 | enum dma_data_direction direction) |
360 | void | |
7bc590b2 | 361 | dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg, int nents, |
9705ef7e | 362 | enum dma_data_direction direction) |
9705ef7e | 363 | |
f311a724 | 364 | Synchronise a single contiguous or scatter/gather mapping for the CPU |
9705ef7e FT |
365 | and device. With the sync_sg API, all the parameters must be the same |
366 | as those passed into the single mapping API. With the sync_single API, | |
367 | you can use dma_handle and size parameters that aren't identical to | |
368 | those passed into the single mapping API to do a partial sync. | |
369 | ||
370 | Notes: You must do this: | |
371 | ||
372 | - Before reading values that have been written by DMA from the device | |
373 | (use the DMA_FROM_DEVICE direction) | |
374 | - After writing values that will be written to the device using DMA | |
375 | (use the DMA_TO_DEVICE) direction | |
376 | - before *and* after handing memory to the device if the memory is | |
377 | DMA_BIDIRECTIONAL | |
378 | ||
379 | See also dma_map_single(). | |
380 | ||
a75b0a2f AK |
381 | dma_addr_t |
382 | dma_map_single_attrs(struct device *dev, void *cpu_addr, size_t size, | |
383 | enum dma_data_direction dir, | |
00085f1e | 384 | unsigned long attrs) |
a75b0a2f AK |
385 | |
386 | void | |
387 | dma_unmap_single_attrs(struct device *dev, dma_addr_t dma_addr, | |
388 | size_t size, enum dma_data_direction dir, | |
00085f1e | 389 | unsigned long attrs) |
a75b0a2f AK |
390 | |
391 | int | |
392 | dma_map_sg_attrs(struct device *dev, struct scatterlist *sgl, | |
393 | int nents, enum dma_data_direction dir, | |
00085f1e | 394 | unsigned long attrs) |
a75b0a2f AK |
395 | |
396 | void | |
397 | dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sgl, | |
398 | int nents, enum dma_data_direction dir, | |
00085f1e | 399 | unsigned long attrs) |
a75b0a2f AK |
400 | |
401 | The four functions above are just like the counterpart functions | |
402 | without the _attrs suffixes, except that they pass an optional | |
00085f1e | 403 | dma_attrs. |
a75b0a2f | 404 | |
77f2ea2f | 405 | The interpretation of DMA attributes is architecture-specific, and |
a75b0a2f AK |
406 | each attribute should be documented in Documentation/DMA-attributes.txt. |
407 | ||
00085f1e KK |
408 | If dma_attrs are 0, the semantics of each of these functions |
409 | is identical to those of the corresponding function | |
a75b0a2f AK |
410 | without the _attrs suffix. As a result dma_map_single_attrs() |
411 | can generally replace dma_map_single(), etc. | |
412 | ||
413 | As an example of the use of the *_attrs functions, here's how | |
414 | you could pass an attribute DMA_ATTR_FOO when mapping memory | |
415 | for DMA: | |
416 | ||
00085f1e KK |
417 | #include <linux/dma-mapping.h> |
418 | /* DMA_ATTR_FOO should be defined in linux/dma-mapping.h and | |
a75b0a2f AK |
419 | * documented in Documentation/DMA-attributes.txt */ |
420 | ... | |
421 | ||
00085f1e KK |
422 | unsigned long attr; |
423 | attr |= DMA_ATTR_FOO; | |
a75b0a2f | 424 | .... |
00085f1e | 425 | n = dma_map_sg_attrs(dev, sg, nents, DMA_TO_DEVICE, attr); |
a75b0a2f AK |
426 | .... |
427 | ||
428 | Architectures that care about DMA_ATTR_FOO would check for its | |
429 | presence in their implementations of the mapping and unmapping | |
430 | routines, e.g.: | |
431 | ||
432 | void whizco_dma_map_sg_attrs(struct device *dev, dma_addr_t dma_addr, | |
433 | size_t size, enum dma_data_direction dir, | |
00085f1e | 434 | unsigned long attrs) |
a75b0a2f AK |
435 | { |
436 | .... | |
00085f1e | 437 | if (attrs & DMA_ATTR_FOO) |
a75b0a2f AK |
438 | /* twizzle the frobnozzle */ |
439 | .... | |
440 | ||
1da177e4 LT |
441 | |
442 | Part II - Advanced dma_ usage | |
443 | ----------------------------- | |
444 | ||
f5a69f4c FT |
445 | Warning: These pieces of the DMA API should not be used in the |
446 | majority of cases, since they cater for unlikely corner cases that | |
447 | don't belong in usual drivers. | |
1da177e4 LT |
448 | |
449 | If you don't understand how cache line coherency works between a | |
450 | processor and an I/O device, you should not be using this part of the | |
451 | API at all. | |
452 | ||
453 | void * | |
454 | dma_alloc_noncoherent(struct device *dev, size_t size, | |
a12e2c6c | 455 | dma_addr_t *dma_handle, gfp_t flag) |
1da177e4 LT |
456 | |
457 | Identical to dma_alloc_coherent() except that the platform will | |
458 | choose to return either consistent or non-consistent memory as it sees | |
459 | fit. By using this API, you are guaranteeing to the platform that you | |
460 | have all the correct and necessary sync points for this memory in the | |
461 | driver should it choose to return non-consistent memory. | |
462 | ||
463 | Note: where the platform can return consistent memory, it will | |
464 | guarantee that the sync points become nops. | |
465 | ||
466 | Warning: Handling non-consistent memory is a real pain. You should | |
77f2ea2f | 467 | only use this API if you positively know your driver will be |
1da177e4 LT |
468 | required to work on one of the rare (usually non-PCI) architectures |
469 | that simply cannot make consistent memory. | |
470 | ||
471 | void | |
472 | dma_free_noncoherent(struct device *dev, size_t size, void *cpu_addr, | |
473 | dma_addr_t dma_handle) | |
474 | ||
a12e2c6c | 475 | Free memory allocated by the nonconsistent API. All parameters must |
1da177e4 LT |
476 | be identical to those passed in (and returned by |
477 | dma_alloc_noncoherent()). | |
478 | ||
1da177e4 LT |
479 | int |
480 | dma_get_cache_alignment(void) | |
481 | ||
a12e2c6c | 482 | Returns the processor cache alignment. This is the absolute minimum |
1da177e4 LT |
483 | alignment *and* width that you must observe when either mapping |
484 | memory or doing partial flushes. | |
485 | ||
486 | Notes: This API may return a number *larger* than the actual cache | |
487 | line, but it will guarantee that one or more cache lines fit exactly | |
488 | into the width returned by this call. It will also always be a power | |
a12e2c6c | 489 | of two for easy alignment. |
1da177e4 | 490 | |
1da177e4 | 491 | void |
d3fa72e4 | 492 | dma_cache_sync(struct device *dev, void *vaddr, size_t size, |
1da177e4 LT |
493 | enum dma_data_direction direction) |
494 | ||
495 | Do a partial sync of memory that was allocated by | |
496 | dma_alloc_noncoherent(), starting at virtual address vaddr and | |
497 | continuing on for size. Again, you *must* observe the cache line | |
498 | boundaries when doing this. | |
499 | ||
500 | int | |
88a984ba | 501 | dma_declare_coherent_memory(struct device *dev, phys_addr_t phys_addr, |
1da177e4 LT |
502 | dma_addr_t device_addr, size_t size, int |
503 | flags) | |
504 | ||
77f2ea2f | 505 | Declare region of memory to be handed out by dma_alloc_coherent() when |
1da177e4 LT |
506 | it's asked for coherent memory for this device. |
507 | ||
f311a724 BH |
508 | phys_addr is the CPU physical address to which the memory is currently |
509 | assigned (this will be ioremapped so the CPU can access the region). | |
1da177e4 | 510 | |
3a9ad0b4 | 511 | device_addr is the DMA address the device needs to be programmed |
88a984ba | 512 | with to actually address this memory (this will be handed out as the |
a12e2c6c | 513 | dma_addr_t in dma_alloc_coherent()). |
1da177e4 LT |
514 | |
515 | size is the size of the area (must be multiples of PAGE_SIZE). | |
516 | ||
77f2ea2f | 517 | flags can be ORed together and are: |
1da177e4 LT |
518 | |
519 | DMA_MEMORY_MAP - request that the memory returned from | |
4ae0edc2 | 520 | dma_alloc_coherent() be directly writable. |
1da177e4 LT |
521 | |
522 | DMA_MEMORY_IO - request that the memory returned from | |
77f2ea2f | 523 | dma_alloc_coherent() be addressable using read()/write()/memcpy_toio() etc. |
1da177e4 | 524 | |
a12e2c6c | 525 | One or both of these flags must be present. |
1da177e4 LT |
526 | |
527 | DMA_MEMORY_INCLUDES_CHILDREN - make the declared memory be allocated by | |
528 | dma_alloc_coherent of any child devices of this one (for memory residing | |
529 | on a bridge). | |
530 | ||
531 | DMA_MEMORY_EXCLUSIVE - only allocate memory from the declared regions. | |
532 | Do not allow dma_alloc_coherent() to fall back to system memory when | |
533 | it's out of memory in the declared region. | |
534 | ||
535 | The return value will be either DMA_MEMORY_MAP or DMA_MEMORY_IO and | |
536 | must correspond to a passed in flag (i.e. no returning DMA_MEMORY_IO | |
537 | if only DMA_MEMORY_MAP were passed in) for success or zero for | |
538 | failure. | |
539 | ||
540 | Note, for DMA_MEMORY_IO returns, all subsequent memory returned by | |
541 | dma_alloc_coherent() may no longer be accessed directly, but instead | |
542 | must be accessed using the correct bus functions. If your driver | |
543 | isn't prepared to handle this contingency, it should not specify | |
544 | DMA_MEMORY_IO in the input flags. | |
545 | ||
546 | As a simplification for the platforms, only *one* such region of | |
547 | memory may be declared per device. | |
548 | ||
549 | For reasons of efficiency, most platforms choose to track the declared | |
550 | region only at the granularity of a page. For smaller allocations, | |
551 | you should use the dma_pool() API. | |
552 | ||
553 | void | |
554 | dma_release_declared_memory(struct device *dev) | |
555 | ||
556 | Remove the memory region previously declared from the system. This | |
557 | API performs *no* in-use checking for this region and will return | |
558 | unconditionally having removed all the required structures. It is the | |
a12e2c6c | 559 | driver's job to ensure that no parts of this memory region are |
1da177e4 LT |
560 | currently in use. |
561 | ||
562 | void * | |
563 | dma_mark_declared_memory_occupied(struct device *dev, | |
564 | dma_addr_t device_addr, size_t size) | |
565 | ||
566 | This is used to occupy specific regions of the declared space | |
567 | (dma_alloc_coherent() will hand out the first free region it finds). | |
568 | ||
a12e2c6c | 569 | device_addr is the *device* address of the region requested. |
1da177e4 | 570 | |
a12e2c6c | 571 | size is the size (and should be a page-sized multiple). |
1da177e4 LT |
572 | |
573 | The return value will be either a pointer to the processor virtual | |
574 | address of the memory, or an error (via PTR_ERR()) if any part of the | |
575 | region is occupied. | |
187f9c3f JR |
576 | |
577 | Part III - Debug drivers use of the DMA-API | |
578 | ------------------------------------------- | |
579 | ||
77f2ea2f | 580 | The DMA-API as described above has some constraints. DMA addresses must be |
187f9c3f JR |
581 | released with the corresponding function with the same size for example. With |
582 | the advent of hardware IOMMUs it becomes more and more important that drivers | |
583 | do not violate those constraints. In the worst case such a violation can | |
584 | result in data corruption up to destroyed filesystems. | |
585 | ||
586 | To debug drivers and find bugs in the usage of the DMA-API checking code can | |
587 | be compiled into the kernel which will tell the developer about those | |
588 | violations. If your architecture supports it you can select the "Enable | |
589 | debugging of DMA-API usage" option in your kernel configuration. Enabling this | |
590 | option has a performance impact. Do not enable it in production kernels. | |
591 | ||
592 | If you boot the resulting kernel will contain code which does some bookkeeping | |
593 | about what DMA memory was allocated for which device. If this code detects an | |
594 | error it prints a warning message with some details into your kernel log. An | |
595 | example warning message may look like this: | |
596 | ||
597 | ------------[ cut here ]------------ | |
598 | WARNING: at /data2/repos/linux-2.6-iommu/lib/dma-debug.c:448 | |
599 | check_unmap+0x203/0x490() | |
600 | Hardware name: | |
601 | forcedeth 0000:00:08.0: DMA-API: device driver frees DMA memory with wrong | |
602 | function [device address=0x00000000640444be] [size=66 bytes] [mapped as | |
603 | single] [unmapped as page] | |
604 | Modules linked in: nfsd exportfs bridge stp llc r8169 | |
605 | Pid: 0, comm: swapper Tainted: G W 2.6.28-dmatest-09289-g8bb99c0 #1 | |
606 | Call Trace: | |
607 | <IRQ> [<ffffffff80240b22>] warn_slowpath+0xf2/0x130 | |
608 | [<ffffffff80647b70>] _spin_unlock+0x10/0x30 | |
609 | [<ffffffff80537e75>] usb_hcd_link_urb_to_ep+0x75/0xc0 | |
610 | [<ffffffff80647c22>] _spin_unlock_irqrestore+0x12/0x40 | |
611 | [<ffffffff8055347f>] ohci_urb_enqueue+0x19f/0x7c0 | |
612 | [<ffffffff80252f96>] queue_work+0x56/0x60 | |
613 | [<ffffffff80237e10>] enqueue_task_fair+0x20/0x50 | |
614 | [<ffffffff80539279>] usb_hcd_submit_urb+0x379/0xbc0 | |
615 | [<ffffffff803b78c3>] cpumask_next_and+0x23/0x40 | |
616 | [<ffffffff80235177>] find_busiest_group+0x207/0x8a0 | |
617 | [<ffffffff8064784f>] _spin_lock_irqsave+0x1f/0x50 | |
618 | [<ffffffff803c7ea3>] check_unmap+0x203/0x490 | |
619 | [<ffffffff803c8259>] debug_dma_unmap_page+0x49/0x50 | |
620 | [<ffffffff80485f26>] nv_tx_done_optimized+0xc6/0x2c0 | |
621 | [<ffffffff80486c13>] nv_nic_irq_optimized+0x73/0x2b0 | |
622 | [<ffffffff8026df84>] handle_IRQ_event+0x34/0x70 | |
623 | [<ffffffff8026ffe9>] handle_edge_irq+0xc9/0x150 | |
624 | [<ffffffff8020e3ab>] do_IRQ+0xcb/0x1c0 | |
625 | [<ffffffff8020c093>] ret_from_intr+0x0/0xa | |
626 | <EOI> <4>---[ end trace f6435a98e2a38c0e ]--- | |
627 | ||
628 | The driver developer can find the driver and the device including a stacktrace | |
629 | of the DMA-API call which caused this warning. | |
630 | ||
631 | Per default only the first error will result in a warning message. All other | |
632 | errors will only silently counted. This limitation exist to prevent the code | |
633 | from flooding your kernel log. To support debugging a device driver this can | |
634 | be disabled via debugfs. See the debugfs interface documentation below for | |
635 | details. | |
636 | ||
637 | The debugfs directory for the DMA-API debugging code is called dma-api/. In | |
638 | this directory the following files can currently be found: | |
639 | ||
640 | dma-api/all_errors This file contains a numeric value. If this | |
641 | value is not equal to zero the debugging code | |
642 | will print a warning for every error it finds | |
19f59460 ML |
643 | into the kernel log. Be careful with this |
644 | option, as it can easily flood your logs. | |
187f9c3f JR |
645 | |
646 | dma-api/disabled This read-only file contains the character 'Y' | |
647 | if the debugging code is disabled. This can | |
648 | happen when it runs out of memory or if it was | |
649 | disabled at boot time | |
650 | ||
651 | dma-api/error_count This file is read-only and shows the total | |
652 | numbers of errors found. | |
653 | ||
654 | dma-api/num_errors The number in this file shows how many | |
655 | warnings will be printed to the kernel log | |
656 | before it stops. This number is initialized to | |
657 | one at system boot and be set by writing into | |
658 | this file | |
659 | ||
660 | dma-api/min_free_entries | |
661 | This read-only file can be read to get the | |
662 | minimum number of free dma_debug_entries the | |
663 | allocator has ever seen. If this value goes | |
664 | down to zero the code will disable itself | |
665 | because it is not longer reliable. | |
666 | ||
667 | dma-api/num_free_entries | |
668 | The current number of free dma_debug_entries | |
669 | in the allocator. | |
670 | ||
016ea687 JR |
671 | dma-api/driver-filter |
672 | You can write a name of a driver into this file | |
673 | to limit the debug output to requests from that | |
674 | particular driver. Write an empty string to | |
675 | that file to disable the filter and see | |
676 | all errors again. | |
677 | ||
187f9c3f JR |
678 | If you have this code compiled into your kernel it will be enabled by default. |
679 | If you want to boot without the bookkeeping anyway you can provide | |
680 | 'dma_debug=off' as a boot parameter. This will disable DMA-API debugging. | |
681 | Notice that you can not enable it again at runtime. You have to reboot to do | |
682 | so. | |
683 | ||
016ea687 JR |
684 | If you want to see debug messages only for a special device driver you can |
685 | specify the dma_debug_driver=<drivername> parameter. This will enable the | |
686 | driver filter at boot time. The debug code will only print errors for that | |
687 | driver afterwards. This filter can be disabled or changed later using debugfs. | |
688 | ||
187f9c3f JR |
689 | When the code disables itself at runtime this is most likely because it ran |
690 | out of dma_debug_entries. These entries are preallocated at boot. The number | |
691 | of preallocated entries is defined per architecture. If it is too low for you | |
692 | boot with 'dma_debug_entries=<your_desired_number>' to overwrite the | |
693 | architectural default. | |
6c9c6d63 | 694 | |
6a08d83e | 695 | void debug_dma_mapping_error(struct device *dev, dma_addr_t dma_addr); |
6c9c6d63 SK |
696 | |
697 | dma-debug interface debug_dma_mapping_error() to debug drivers that fail | |
77f2ea2f | 698 | to check DMA mapping errors on addresses returned by dma_map_single() and |
6c9c6d63 SK |
699 | dma_map_page() interfaces. This interface clears a flag set by |
700 | debug_dma_map_page() to indicate that dma_mapping_error() has been called by | |
701 | the driver. When driver does unmap, debug_dma_unmap() checks the flag and if | |
702 | this flag is still set, prints warning message that includes call trace that | |
703 | leads up to the unmap. This interface can be called from dma_mapping_error() | |
77f2ea2f | 704 | routines to enable DMA mapping error check debugging. |
6c9c6d63 | 705 |