Version:  2.0.40 2.2.26 2.4.37 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3


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

This page was automatically generated by LXR 0.3.1 (source).  •  Linux is a registered trademark of Linus Torvalds  •  Contact us