linux-3.3/Documentation/DMA-API.txt

6 This document describes the DMA API.  For a more gentle introduction
7 of the API (and actual examples) see
8 Documentation/DMA-API-HOWTO.txt.
10 This API is split into two pieces.  Part I describes the API.  Part II
11 describes the extensions to the API for supporting non-consistent
14 platforms) you should only use the API described in part I.
16 Part I - dma_ API
19 To get the dma_ API, you must #include <linux/dma-mapping.h>
76 To get this part of the dma_ API, you must #include <linux/dmapool.h>
141 internal API for use by the platform than an external API for use by
163 This API returns the mask that the platform requires to
184 The direction for both api's may be converted freely by casting.
185 However the dma_ API uses a strongly typed enumerator for its
194 API.  Further, regions that appear to be physically contiguous in
196 this API does not provide any scatter/gather capability, it will fail
198 For this reason, it is recommended that memory mapped by this API be
220 line width.  In order for memory mapped by this API to operate
224 may not be known at compile time, the API will not enforce this
257 API.
267 API for mapping and unmapping for pages.  All the notes and warnings
327 API.
346 and device. With the sync_sg API, all the parameters must be the same
347 as those passed into the single mapping API. With the sync_single API,
349 those passed into the single mapping API to do a partial sync.
431 Warning: These pieces of the DMA API should not be used in the
437 API at all.
445 fit.  By using this API, you are guaranteeing to the platform that you
453 only ever use this API if you positively know your driver will be
461 Free memory allocated by the nonconsistent API.  All parameters must
472 Notes: This API may return a number *larger* than the actual cache
538 you should use the dma_pool() API.
544 API performs *no* in-use checking for this region and will return
564 Part III - Debug drivers use of the DMA-API
567 The DMA-API as described above as some constraints. DMA addresses must be
573 To debug drivers and find bugs in the usage of the DMA-API checking code can
576 debugging of DMA-API usage" option in your kernel configuration. Enabling this
588 forcedeth 0000:00:08.0: DMA-API: device driver frees DMA memory with wrong
616 of the DMA-API call which caused this warning.
624 The debugfs directory for the DMA-API debugging code is called dma-api/. In
627 	dma-api/all_errors	This file contains a numeric value. If this
633 	dma-api/disabled	This read-only file contains the character 'Y'
638 	dma-api/error_count	This file is read-only and shows the total
641 	dma-api/num_errors	The number in this file shows how many
647 	dma-api/min_free_entries
654 	dma-api/num_free_entries
658 	dma-api/driver-filter
667 'dma_debug=off' as a boot parameter. This will disable DMA-API debugging.