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Linus Torvalds1da177e2005-04-16 15:20:36 -07001 Dynamic DMA mapping using the generic device
2 ============================================
3
4 James E.J. Bottomley <James.Bottomley@HansenPartnership.com>
5
6This document describes the DMA API. For a more gentle introduction
7phrased in terms of the pci_ equivalents (and actual examples) see
Randy Dunlap5872fb92009-01-29 16:28:02 -08008Documentation/PCI/PCI-DMA-mapping.txt.
Linus Torvalds1da177e2005-04-16 15:20:36 -07009
10This API is split into two pieces. Part I describes the API and the
11corresponding pci_ API. Part II describes the extensions to the API
12for supporting non-consistent memory machines. Unless you know that
13your driver absolutely has to support non-consistent platforms (this
14is usually only legacy platforms) you should only use the API
15described in part I.
16
17Part I - pci_ and dma_ Equivalent API
18-------------------------------------
19
20To get the pci_ API, you must #include <linux/pci.h>
21To get the dma_ API, you must #include <linux/dma-mapping.h>
22
23
24Part Ia - Using large dma-coherent buffers
25------------------------------------------
26
27void *
28dma_alloc_coherent(struct device *dev, size_t size,
Randy Dunlapa12e2c62007-07-31 00:38:17 -070029 dma_addr_t *dma_handle, gfp_t flag)
Linus Torvalds1da177e2005-04-16 15:20:36 -070030void *
31pci_alloc_consistent(struct pci_dev *dev, size_t size,
32 dma_addr_t *dma_handle)
33
34Consistent memory is memory for which a write by either the device or
35the processor can immediately be read by the processor or device
David Brownell21440d32006-04-01 10:21:52 -080036without having to worry about caching effects. (You may however need
37to make sure to flush the processor's write buffers before telling
38devices to read that memory.)
Linus Torvalds1da177e2005-04-16 15:20:36 -070039
40This routine allocates a region of <size> bytes of consistent memory.
Randy Dunlapa12e2c62007-07-31 00:38:17 -070041It also returns a <dma_handle> which may be cast to an unsigned
Linus Torvalds1da177e2005-04-16 15:20:36 -070042integer the same width as the bus and used as the physical address
43base of the region.
44
45Returns: a pointer to the allocated region (in the processor's virtual
46address space) or NULL if the allocation failed.
47
48Note: consistent memory can be expensive on some platforms, and the
49minimum allocation length may be as big as a page, so you should
50consolidate your requests for consistent memory as much as possible.
51The simplest way to do that is to use the dma_pool calls (see below).
52
53The flag parameter (dma_alloc_coherent only) allows the caller to
54specify the GFP_ flags (see kmalloc) for the allocation (the
Randy Dunlapa12e2c62007-07-31 00:38:17 -070055implementation may choose to ignore flags that affect the location of
Linus Torvalds1da177e2005-04-16 15:20:36 -070056the returned memory, like GFP_DMA). For pci_alloc_consistent, you
57must assume GFP_ATOMIC behaviour.
58
59void
Randy Dunlapa12e2c62007-07-31 00:38:17 -070060dma_free_coherent(struct device *dev, size_t size, void *cpu_addr,
Linus Torvalds1da177e2005-04-16 15:20:36 -070061 dma_addr_t dma_handle)
62void
Randy Dunlapa12e2c62007-07-31 00:38:17 -070063pci_free_consistent(struct pci_dev *dev, size_t size, void *cpu_addr,
Linus Torvalds1da177e2005-04-16 15:20:36 -070064 dma_addr_t dma_handle)
65
66Free the region of consistent memory you previously allocated. dev,
67size and dma_handle must all be the same as those passed into the
68consistent allocate. cpu_addr must be the virtual address returned by
Randy Dunlapa12e2c62007-07-31 00:38:17 -070069the consistent allocate.
Linus Torvalds1da177e2005-04-16 15:20:36 -070070
David Brownellaa248862007-08-10 13:10:27 -070071Note that unlike their sibling allocation calls, these routines
72may only be called with IRQs enabled.
73
Linus Torvalds1da177e2005-04-16 15:20:36 -070074
75Part Ib - Using small dma-coherent buffers
76------------------------------------------
77
78To get this part of the dma_ API, you must #include <linux/dmapool.h>
79
80Many drivers need lots of small dma-coherent memory regions for DMA
81descriptors or I/O buffers. Rather than allocating in units of a page
82or more using dma_alloc_coherent(), you can use DMA pools. These work
Randy Dunlapa12e2c62007-07-31 00:38:17 -070083much like a struct kmem_cache, except that they use the dma-coherent allocator,
Linus Torvalds1da177e2005-04-16 15:20:36 -070084not __get_free_pages(). Also, they understand common hardware constraints
Randy Dunlapa12e2c62007-07-31 00:38:17 -070085for alignment, like queue heads needing to be aligned on N-byte boundaries.
Linus Torvalds1da177e2005-04-16 15:20:36 -070086
87
88 struct dma_pool *
89 dma_pool_create(const char *name, struct device *dev,
90 size_t size, size_t align, size_t alloc);
91
92 struct pci_pool *
93 pci_pool_create(const char *name, struct pci_device *dev,
94 size_t size, size_t align, size_t alloc);
95
96The pool create() routines initialize a pool of dma-coherent buffers
97for use with a given device. It must be called in a context which
98can sleep.
99
Christoph Lametere18b8902006-12-06 20:33:20 -0800100The "name" is for diagnostics (like a struct kmem_cache name); dev and size
Linus Torvalds1da177e2005-04-16 15:20:36 -0700101are like what you'd pass to dma_alloc_coherent(). The device's hardware
102alignment requirement for this type of data is "align" (which is expressed
103in bytes, and must be a power of two). If your device has no boundary
104crossing restrictions, pass 0 for alloc; passing 4096 says memory allocated
105from this pool must not cross 4KByte boundaries.
106
107
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700108 void *dma_pool_alloc(struct dma_pool *pool, gfp_t gfp_flags,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700109 dma_addr_t *dma_handle);
110
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700111 void *pci_pool_alloc(struct pci_pool *pool, gfp_t gfp_flags,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700112 dma_addr_t *dma_handle);
113
114This allocates memory from the pool; the returned memory will meet the size
115and alignment requirements specified at creation time. Pass GFP_ATOMIC to
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700116prevent blocking, or if it's permitted (not in_interrupt, not holding SMP locks),
Linus Torvalds1da177e2005-04-16 15:20:36 -0700117pass GFP_KERNEL to allow blocking. Like dma_alloc_coherent(), this returns
118two values: an address usable by the cpu, and the dma address usable by the
119pool's device.
120
121
122 void dma_pool_free(struct dma_pool *pool, void *vaddr,
123 dma_addr_t addr);
124
125 void pci_pool_free(struct pci_pool *pool, void *vaddr,
126 dma_addr_t addr);
127
128This puts memory back into the pool. The pool is what was passed to
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700129the pool allocation routine; the cpu (vaddr) and dma addresses are what
Linus Torvalds1da177e2005-04-16 15:20:36 -0700130were returned when that routine allocated the memory being freed.
131
132
133 void dma_pool_destroy(struct dma_pool *pool);
134
135 void pci_pool_destroy(struct pci_pool *pool);
136
137The pool destroy() routines free the resources of the pool. They must be
138called in a context which can sleep. Make sure you've freed all allocated
139memory back to the pool before you destroy it.
140
141
142Part Ic - DMA addressing limitations
143------------------------------------
144
145int
146dma_supported(struct device *dev, u64 mask)
147int
Randy Dunlap02d15c42008-04-29 01:00:35 -0700148pci_dma_supported(struct pci_dev *hwdev, u64 mask)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700149
150Checks to see if the device can support DMA to the memory described by
151mask.
152
153Returns: 1 if it can and 0 if it can't.
154
155Notes: This routine merely tests to see if the mask is possible. It
156won't change the current mask settings. It is more intended as an
157internal API for use by the platform than an external API for use by
158driver writers.
159
160int
161dma_set_mask(struct device *dev, u64 mask)
162int
163pci_set_dma_mask(struct pci_device *dev, u64 mask)
164
165Checks to see if the mask is possible and updates the device
166parameters if it is.
167
168Returns: 0 if successful and a negative error if not.
169
170u64
171dma_get_required_mask(struct device *dev)
172
John Keller175add12008-11-24 16:47:17 -0600173This API returns the mask that the platform requires to
174operate efficiently. Usually this means the returned mask
Linus Torvalds1da177e2005-04-16 15:20:36 -0700175is the minimum required to cover all of memory. Examining the
176required mask gives drivers with variable descriptor sizes the
177opportunity to use smaller descriptors as necessary.
178
179Requesting the required mask does not alter the current mask. If you
John Keller175add12008-11-24 16:47:17 -0600180wish to take advantage of it, you should issue a dma_set_mask()
181call to set the mask to the value returned.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700182
183
184Part Id - Streaming DMA mappings
185--------------------------------
186
187dma_addr_t
188dma_map_single(struct device *dev, void *cpu_addr, size_t size,
189 enum dma_data_direction direction)
190dma_addr_t
Randy Dunlap02d15c42008-04-29 01:00:35 -0700191pci_map_single(struct pci_dev *hwdev, void *cpu_addr, size_t size,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700192 int direction)
193
194Maps a piece of processor virtual memory so it can be accessed by the
195device and returns the physical handle of the memory.
196
197The direction for both api's may be converted freely by casting.
198However the dma_ API uses a strongly typed enumerator for its
199direction:
200
201DMA_NONE = PCI_DMA_NONE no direction (used for
202 debugging)
203DMA_TO_DEVICE = PCI_DMA_TODEVICE data is going from the
204 memory to the device
205DMA_FROM_DEVICE = PCI_DMA_FROMDEVICE data is coming from
206 the device to the
207 memory
208DMA_BIDIRECTIONAL = PCI_DMA_BIDIRECTIONAL direction isn't known
209
210Notes: Not all memory regions in a machine can be mapped by this
211API. Further, regions that appear to be physically contiguous in
212kernel virtual space may not be contiguous as physical memory. Since
213this API does not provide any scatter/gather capability, it will fail
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700214if the user tries to map a non-physically contiguous piece of memory.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700215For this reason, it is recommended that memory mapped by this API be
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700216obtained only from sources which guarantee it to be physically contiguous
Linus Torvalds1da177e2005-04-16 15:20:36 -0700217(like kmalloc).
218
219Further, the physical address of the memory must be within the
220dma_mask of the device (the dma_mask represents a bit mask of the
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700221addressable region for the device. I.e., if the physical address of
Linus Torvalds1da177e2005-04-16 15:20:36 -0700222the memory anded with the dma_mask is still equal to the physical
223address, then the device can perform DMA to the memory). In order to
224ensure that the memory allocated by kmalloc is within the dma_mask,
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700225the driver may specify various platform-dependent flags to restrict
Linus Torvalds1da177e2005-04-16 15:20:36 -0700226the physical memory range of the allocation (e.g. on x86, GFP_DMA
227guarantees to be within the first 16Mb of available physical memory,
228as required by ISA devices).
229
230Note also that the above constraints on physical contiguity and
231dma_mask may not apply if the platform has an IOMMU (a device which
232supplies a physical to virtual mapping between the I/O memory bus and
233the device). However, to be portable, device driver writers may *not*
234assume that such an IOMMU exists.
235
236Warnings: Memory coherency operates at a granularity called the cache
237line width. In order for memory mapped by this API to operate
238correctly, the mapped region must begin exactly on a cache line
239boundary and end exactly on one (to prevent two separately mapped
240regions from sharing a single cache line). Since the cache line size
241may not be known at compile time, the API will not enforce this
242requirement. Therefore, it is recommended that driver writers who
243don't take special care to determine the cache line size at run time
244only map virtual regions that begin and end on page boundaries (which
245are guaranteed also to be cache line boundaries).
246
247DMA_TO_DEVICE synchronisation must be done after the last modification
248of the memory region by the software and before it is handed off to
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700249the driver. Once this primitive is used, memory covered by this
250primitive should be treated as read-only by the device. If the device
Linus Torvalds1da177e2005-04-16 15:20:36 -0700251may write to it at any point, it should be DMA_BIDIRECTIONAL (see
252below).
253
254DMA_FROM_DEVICE synchronisation must be done before the driver
255accesses data that may be changed by the device. This memory should
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700256be treated as read-only by the driver. If the driver needs to write
Linus Torvalds1da177e2005-04-16 15:20:36 -0700257to it at any point, it should be DMA_BIDIRECTIONAL (see below).
258
259DMA_BIDIRECTIONAL requires special handling: it means that the driver
260isn't sure if the memory was modified before being handed off to the
261device and also isn't sure if the device will also modify it. Thus,
262you must always sync bidirectional memory twice: once before the
263memory is handed off to the device (to make sure all memory changes
264are flushed from the processor) and once before the data may be
265accessed after being used by the device (to make sure any processor
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700266cache lines are updated with data that the device may have changed).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700267
268void
269dma_unmap_single(struct device *dev, dma_addr_t dma_addr, size_t size,
270 enum dma_data_direction direction)
271void
272pci_unmap_single(struct pci_dev *hwdev, dma_addr_t dma_addr,
273 size_t size, int direction)
274
275Unmaps the region previously mapped. All the parameters passed in
276must be identical to those passed in (and returned) by the mapping
277API.
278
279dma_addr_t
280dma_map_page(struct device *dev, struct page *page,
281 unsigned long offset, size_t size,
282 enum dma_data_direction direction)
283dma_addr_t
284pci_map_page(struct pci_dev *hwdev, struct page *page,
285 unsigned long offset, size_t size, int direction)
286void
287dma_unmap_page(struct device *dev, dma_addr_t dma_address, size_t size,
288 enum dma_data_direction direction)
289void
290pci_unmap_page(struct pci_dev *hwdev, dma_addr_t dma_address,
291 size_t size, int direction)
292
293API for mapping and unmapping for pages. All the notes and warnings
294for the other mapping APIs apply here. Also, although the <offset>
295and <size> parameters are provided to do partial page mapping, it is
296recommended that you never use these unless you really know what the
297cache width is.
298
299int
FUJITA Tomonori8d8bb392008-07-25 19:44:49 -0700300dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700301
302int
FUJITA Tomonori8d8bb392008-07-25 19:44:49 -0700303pci_dma_mapping_error(struct pci_dev *hwdev, dma_addr_t dma_addr)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700304
305In some circumstances dma_map_single and dma_map_page will fail to create
306a mapping. A driver can check for these errors by testing the returned
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700307dma address with dma_mapping_error(). A non-zero return value means the mapping
308could not be created and the driver should take appropriate action (e.g.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700309reduce current DMA mapping usage or delay and try again later).
310
David Brownell21440d32006-04-01 10:21:52 -0800311 int
312 dma_map_sg(struct device *dev, struct scatterlist *sg,
313 int nents, enum dma_data_direction direction)
314 int
315 pci_map_sg(struct pci_dev *hwdev, struct scatterlist *sg,
316 int nents, int direction)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700317
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700318Returns: the number of physical segments mapped (this may be shorter
FUJITA Tomonori1d678f32008-12-01 13:14:01 -0800319than <nents> passed in if some elements of the scatter/gather list are
320physically or virtually adjacent and an IOMMU maps them with a single
321entry).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700322
323Please note that the sg cannot be mapped again if it has been mapped once.
324The mapping process is allowed to destroy information in the sg.
325
326As with the other mapping interfaces, dma_map_sg can fail. When it
327does, 0 is returned and a driver must take appropriate action. It is
328critical that the driver do something, in the case of a block driver
329aborting the request or even oopsing is better than doing nothing and
330corrupting the filesystem.
331
David Brownell21440d32006-04-01 10:21:52 -0800332With scatterlists, you use the resulting mapping like this:
333
334 int i, count = dma_map_sg(dev, sglist, nents, direction);
335 struct scatterlist *sg;
336
FUJITA Tomonori79eb0142008-09-18 09:35:28 -0700337 for_each_sg(sglist, sg, count, i) {
David Brownell21440d32006-04-01 10:21:52 -0800338 hw_address[i] = sg_dma_address(sg);
339 hw_len[i] = sg_dma_len(sg);
340 }
341
342where nents is the number of entries in the sglist.
343
344The implementation is free to merge several consecutive sglist entries
345into one (e.g. with an IOMMU, or if several pages just happen to be
346physically contiguous) and returns the actual number of sg entries it
347mapped them to. On failure 0, is returned.
348
349Then you should loop count times (note: this can be less than nents times)
350and use sg_dma_address() and sg_dma_len() macros where you previously
351accessed sg->address and sg->length as shown above.
352
353 void
354 dma_unmap_sg(struct device *dev, struct scatterlist *sg,
355 int nhwentries, enum dma_data_direction direction)
356 void
357 pci_unmap_sg(struct pci_dev *hwdev, struct scatterlist *sg,
358 int nents, int direction)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700359
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700360Unmap the previously mapped scatter/gather list. All the parameters
Linus Torvalds1da177e2005-04-16 15:20:36 -0700361must be the same as those and passed in to the scatter/gather mapping
362API.
363
364Note: <nents> must be the number you passed in, *not* the number of
365physical entries returned.
366
367void
368dma_sync_single(struct device *dev, dma_addr_t dma_handle, size_t size,
369 enum dma_data_direction direction)
370void
371pci_dma_sync_single(struct pci_dev *hwdev, dma_addr_t dma_handle,
372 size_t size, int direction)
373void
374dma_sync_sg(struct device *dev, struct scatterlist *sg, int nelems,
375 enum dma_data_direction direction)
376void
377pci_dma_sync_sg(struct pci_dev *hwdev, struct scatterlist *sg,
378 int nelems, int direction)
379
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700380Synchronise a single contiguous or scatter/gather mapping. All the
Linus Torvalds1da177e2005-04-16 15:20:36 -0700381parameters must be the same as those passed into the single mapping
382API.
383
384Notes: You must do this:
385
386- Before reading values that have been written by DMA from the device
387 (use the DMA_FROM_DEVICE direction)
388- After writing values that will be written to the device using DMA
389 (use the DMA_TO_DEVICE) direction
390- before *and* after handing memory to the device if the memory is
391 DMA_BIDIRECTIONAL
392
393See also dma_map_single().
394
Arthur Kepnera75b0a22008-04-29 01:00:31 -0700395dma_addr_t
396dma_map_single_attrs(struct device *dev, void *cpu_addr, size_t size,
397 enum dma_data_direction dir,
398 struct dma_attrs *attrs)
399
400void
401dma_unmap_single_attrs(struct device *dev, dma_addr_t dma_addr,
402 size_t size, enum dma_data_direction dir,
403 struct dma_attrs *attrs)
404
405int
406dma_map_sg_attrs(struct device *dev, struct scatterlist *sgl,
407 int nents, enum dma_data_direction dir,
408 struct dma_attrs *attrs)
409
410void
411dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sgl,
412 int nents, enum dma_data_direction dir,
413 struct dma_attrs *attrs)
414
415The four functions above are just like the counterpart functions
416without the _attrs suffixes, except that they pass an optional
417struct dma_attrs*.
418
419struct dma_attrs encapsulates a set of "dma attributes". For the
420definition of struct dma_attrs see linux/dma-attrs.h.
421
422The interpretation of dma attributes is architecture-specific, and
423each attribute should be documented in Documentation/DMA-attributes.txt.
424
425If struct dma_attrs* is NULL, the semantics of each of these
426functions is identical to those of the corresponding function
427without the _attrs suffix. As a result dma_map_single_attrs()
428can generally replace dma_map_single(), etc.
429
430As an example of the use of the *_attrs functions, here's how
431you could pass an attribute DMA_ATTR_FOO when mapping memory
432for DMA:
433
434#include <linux/dma-attrs.h>
435/* DMA_ATTR_FOO should be defined in linux/dma-attrs.h and
436 * documented in Documentation/DMA-attributes.txt */
437...
438
439 DEFINE_DMA_ATTRS(attrs);
440 dma_set_attr(DMA_ATTR_FOO, &attrs);
441 ....
442 n = dma_map_sg_attrs(dev, sg, nents, DMA_TO_DEVICE, &attr);
443 ....
444
445Architectures that care about DMA_ATTR_FOO would check for its
446presence in their implementations of the mapping and unmapping
447routines, e.g.:
448
449void whizco_dma_map_sg_attrs(struct device *dev, dma_addr_t dma_addr,
450 size_t size, enum dma_data_direction dir,
451 struct dma_attrs *attrs)
452{
453 ....
454 int foo = dma_get_attr(DMA_ATTR_FOO, attrs);
455 ....
456 if (foo)
457 /* twizzle the frobnozzle */
458 ....
459
Linus Torvalds1da177e2005-04-16 15:20:36 -0700460
461Part II - Advanced dma_ usage
462-----------------------------
463
464Warning: These pieces of the DMA API have no PCI equivalent. They
465should also not be used in the majority of cases, since they cater for
466unlikely corner cases that don't belong in usual drivers.
467
468If you don't understand how cache line coherency works between a
469processor and an I/O device, you should not be using this part of the
470API at all.
471
472void *
473dma_alloc_noncoherent(struct device *dev, size_t size,
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700474 dma_addr_t *dma_handle, gfp_t flag)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700475
476Identical to dma_alloc_coherent() except that the platform will
477choose to return either consistent or non-consistent memory as it sees
478fit. By using this API, you are guaranteeing to the platform that you
479have all the correct and necessary sync points for this memory in the
480driver should it choose to return non-consistent memory.
481
482Note: where the platform can return consistent memory, it will
483guarantee that the sync points become nops.
484
485Warning: Handling non-consistent memory is a real pain. You should
486only ever use this API if you positively know your driver will be
487required to work on one of the rare (usually non-PCI) architectures
488that simply cannot make consistent memory.
489
490void
491dma_free_noncoherent(struct device *dev, size_t size, void *cpu_addr,
492 dma_addr_t dma_handle)
493
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700494Free memory allocated by the nonconsistent API. All parameters must
Linus Torvalds1da177e2005-04-16 15:20:36 -0700495be identical to those passed in (and returned by
496dma_alloc_noncoherent()).
497
498int
Ralf Baechlef67637e2006-12-06 20:38:54 -0800499dma_is_consistent(struct device *dev, dma_addr_t dma_handle)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700500
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700501Returns true if the device dev is performing consistent DMA on the memory
Ralf Baechlef67637e2006-12-06 20:38:54 -0800502area pointed to by the dma_handle.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700503
504int
505dma_get_cache_alignment(void)
506
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700507Returns the processor cache alignment. This is the absolute minimum
Linus Torvalds1da177e2005-04-16 15:20:36 -0700508alignment *and* width that you must observe when either mapping
509memory or doing partial flushes.
510
511Notes: This API may return a number *larger* than the actual cache
512line, but it will guarantee that one or more cache lines fit exactly
513into the width returned by this call. It will also always be a power
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700514of two for easy alignment.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700515
516void
517dma_sync_single_range(struct device *dev, dma_addr_t dma_handle,
518 unsigned long offset, size_t size,
519 enum dma_data_direction direction)
520
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700521Does a partial sync, starting at offset and continuing for size. You
Linus Torvalds1da177e2005-04-16 15:20:36 -0700522must be careful to observe the cache alignment and width when doing
523anything like this. You must also be extra careful about accessing
524memory you intend to sync partially.
525
526void
Ralf Baechled3fa72e2006-12-06 20:38:56 -0800527dma_cache_sync(struct device *dev, void *vaddr, size_t size,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700528 enum dma_data_direction direction)
529
530Do a partial sync of memory that was allocated by
531dma_alloc_noncoherent(), starting at virtual address vaddr and
532continuing on for size. Again, you *must* observe the cache line
533boundaries when doing this.
534
535int
536dma_declare_coherent_memory(struct device *dev, dma_addr_t bus_addr,
537 dma_addr_t device_addr, size_t size, int
538 flags)
539
Linus Torvalds1da177e2005-04-16 15:20:36 -0700540Declare region of memory to be handed out by dma_alloc_coherent when
541it's asked for coherent memory for this device.
542
543bus_addr is the physical address to which the memory is currently
544assigned in the bus responding region (this will be used by the
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700545platform to perform the mapping).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700546
547device_addr is the physical address the device needs to be programmed
548with actually to address this memory (this will be handed out as the
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700549dma_addr_t in dma_alloc_coherent()).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700550
551size is the size of the area (must be multiples of PAGE_SIZE).
552
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700553flags can be or'd together and are:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700554
555DMA_MEMORY_MAP - request that the memory returned from
Matt LaPlante4ae0edc2006-11-30 04:58:40 +0100556dma_alloc_coherent() be directly writable.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700557
558DMA_MEMORY_IO - request that the memory returned from
559dma_alloc_coherent() be addressable using read/write/memcpy_toio etc.
560
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700561One or both of these flags must be present.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700562
563DMA_MEMORY_INCLUDES_CHILDREN - make the declared memory be allocated by
564dma_alloc_coherent of any child devices of this one (for memory residing
565on a bridge).
566
567DMA_MEMORY_EXCLUSIVE - only allocate memory from the declared regions.
568Do not allow dma_alloc_coherent() to fall back to system memory when
569it's out of memory in the declared region.
570
571The return value will be either DMA_MEMORY_MAP or DMA_MEMORY_IO and
572must correspond to a passed in flag (i.e. no returning DMA_MEMORY_IO
573if only DMA_MEMORY_MAP were passed in) for success or zero for
574failure.
575
576Note, for DMA_MEMORY_IO returns, all subsequent memory returned by
577dma_alloc_coherent() may no longer be accessed directly, but instead
578must be accessed using the correct bus functions. If your driver
579isn't prepared to handle this contingency, it should not specify
580DMA_MEMORY_IO in the input flags.
581
582As a simplification for the platforms, only *one* such region of
583memory may be declared per device.
584
585For reasons of efficiency, most platforms choose to track the declared
586region only at the granularity of a page. For smaller allocations,
587you should use the dma_pool() API.
588
589void
590dma_release_declared_memory(struct device *dev)
591
592Remove the memory region previously declared from the system. This
593API performs *no* in-use checking for this region and will return
594unconditionally having removed all the required structures. It is the
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700595driver's job to ensure that no parts of this memory region are
Linus Torvalds1da177e2005-04-16 15:20:36 -0700596currently in use.
597
598void *
599dma_mark_declared_memory_occupied(struct device *dev,
600 dma_addr_t device_addr, size_t size)
601
602This is used to occupy specific regions of the declared space
603(dma_alloc_coherent() will hand out the first free region it finds).
604
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700605device_addr is the *device* address of the region requested.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700606
Randy Dunlapa12e2c62007-07-31 00:38:17 -0700607size is the size (and should be a page-sized multiple).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700608
609The return value will be either a pointer to the processor virtual
610address of the memory, or an error (via PTR_ERR()) if any part of the
611region is occupied.
Joerg Roedel187f9c32009-01-09 16:28:07 +0100612
613Part III - Debug drivers use of the DMA-API
614-------------------------------------------
615
616The DMA-API as described above as some constraints. DMA addresses must be
617released with the corresponding function with the same size for example. With
618the advent of hardware IOMMUs it becomes more and more important that drivers
619do not violate those constraints. In the worst case such a violation can
620result in data corruption up to destroyed filesystems.
621
622To debug drivers and find bugs in the usage of the DMA-API checking code can
623be compiled into the kernel which will tell the developer about those
624violations. If your architecture supports it you can select the "Enable
625debugging of DMA-API usage" option in your kernel configuration. Enabling this
626option has a performance impact. Do not enable it in production kernels.
627
628If you boot the resulting kernel will contain code which does some bookkeeping
629about what DMA memory was allocated for which device. If this code detects an
630error it prints a warning message with some details into your kernel log. An
631example warning message may look like this:
632
633------------[ cut here ]------------
634WARNING: at /data2/repos/linux-2.6-iommu/lib/dma-debug.c:448
635 check_unmap+0x203/0x490()
636Hardware name:
637forcedeth 0000:00:08.0: DMA-API: device driver frees DMA memory with wrong
638 function [device address=0x00000000640444be] [size=66 bytes] [mapped as
639single] [unmapped as page]
640Modules linked in: nfsd exportfs bridge stp llc r8169
641Pid: 0, comm: swapper Tainted: G W 2.6.28-dmatest-09289-g8bb99c0 #1
642Call Trace:
643 <IRQ> [<ffffffff80240b22>] warn_slowpath+0xf2/0x130
644 [<ffffffff80647b70>] _spin_unlock+0x10/0x30
645 [<ffffffff80537e75>] usb_hcd_link_urb_to_ep+0x75/0xc0
646 [<ffffffff80647c22>] _spin_unlock_irqrestore+0x12/0x40
647 [<ffffffff8055347f>] ohci_urb_enqueue+0x19f/0x7c0
648 [<ffffffff80252f96>] queue_work+0x56/0x60
649 [<ffffffff80237e10>] enqueue_task_fair+0x20/0x50
650 [<ffffffff80539279>] usb_hcd_submit_urb+0x379/0xbc0
651 [<ffffffff803b78c3>] cpumask_next_and+0x23/0x40
652 [<ffffffff80235177>] find_busiest_group+0x207/0x8a0
653 [<ffffffff8064784f>] _spin_lock_irqsave+0x1f/0x50
654 [<ffffffff803c7ea3>] check_unmap+0x203/0x490
655 [<ffffffff803c8259>] debug_dma_unmap_page+0x49/0x50
656 [<ffffffff80485f26>] nv_tx_done_optimized+0xc6/0x2c0
657 [<ffffffff80486c13>] nv_nic_irq_optimized+0x73/0x2b0
658 [<ffffffff8026df84>] handle_IRQ_event+0x34/0x70
659 [<ffffffff8026ffe9>] handle_edge_irq+0xc9/0x150
660 [<ffffffff8020e3ab>] do_IRQ+0xcb/0x1c0
661 [<ffffffff8020c093>] ret_from_intr+0x0/0xa
662 <EOI> <4>---[ end trace f6435a98e2a38c0e ]---
663
664The driver developer can find the driver and the device including a stacktrace
665of the DMA-API call which caused this warning.
666
667Per default only the first error will result in a warning message. All other
668errors will only silently counted. This limitation exist to prevent the code
669from flooding your kernel log. To support debugging a device driver this can
670be disabled via debugfs. See the debugfs interface documentation below for
671details.
672
673The debugfs directory for the DMA-API debugging code is called dma-api/. In
674this directory the following files can currently be found:
675
676 dma-api/all_errors This file contains a numeric value. If this
677 value is not equal to zero the debugging code
678 will print a warning for every error it finds
679 into the kernel log. Be carefull with this
680 option. It can easily flood your logs.
681
682 dma-api/disabled This read-only file contains the character 'Y'
683 if the debugging code is disabled. This can
684 happen when it runs out of memory or if it was
685 disabled at boot time
686
687 dma-api/error_count This file is read-only and shows the total
688 numbers of errors found.
689
690 dma-api/num_errors The number in this file shows how many
691 warnings will be printed to the kernel log
692 before it stops. This number is initialized to
693 one at system boot and be set by writing into
694 this file
695
696 dma-api/min_free_entries
697 This read-only file can be read to get the
698 minimum number of free dma_debug_entries the
699 allocator has ever seen. If this value goes
700 down to zero the code will disable itself
701 because it is not longer reliable.
702
703 dma-api/num_free_entries
704 The current number of free dma_debug_entries
705 in the allocator.
706
Joerg Roedel016ea682009-05-22 21:57:23 +0200707 dma-api/driver-filter
708 You can write a name of a driver into this file
709 to limit the debug output to requests from that
710 particular driver. Write an empty string to
711 that file to disable the filter and see
712 all errors again.
713
Joerg Roedel187f9c32009-01-09 16:28:07 +0100714If you have this code compiled into your kernel it will be enabled by default.
715If you want to boot without the bookkeeping anyway you can provide
716'dma_debug=off' as a boot parameter. This will disable DMA-API debugging.
717Notice that you can not enable it again at runtime. You have to reboot to do
718so.
719
Joerg Roedel016ea682009-05-22 21:57:23 +0200720If you want to see debug messages only for a special device driver you can
721specify the dma_debug_driver=<drivername> parameter. This will enable the
722driver filter at boot time. The debug code will only print errors for that
723driver afterwards. This filter can be disabled or changed later using debugfs.
724
Joerg Roedel187f9c32009-01-09 16:28:07 +0100725When the code disables itself at runtime this is most likely because it ran
726out of dma_debug_entries. These entries are preallocated at boot. The number
727of preallocated entries is defined per architecture. If it is too low for you
728boot with 'dma_debug_entries=<your_desired_number>' to overwrite the
729architectural default.