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Commit 1d678f36 authored by FUJITA Tomonori's avatar FUJITA Tomonori Committed by Linus Torvalds
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DMA-API.txt: fix description of pci_map_sg/dma_map_sg scatterlists handling 



- pci_map_sg/dma_map_sg are used with a scatter gather list that doesn't
  come from the block layer (e.g.  some network drivers do).

- how IOMMUs merge adjacent elements of the scatter/gather list is
  independent of how the block layer determines sees elements.

Signed-off-by: default avatarFUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 4280e312

Documentation/DMA-API.txt

+3 −5
Original line number Diff line number Diff line
@@ -316,12 +316,10 @@ reduce current DMA mapping usage or delay and try again later). 
	pci_map_sg(struct pci_dev *hwdev, struct scatterlist *sg,

		int nents, int direction)



Maps a scatter gather list from the block layer.



Returns: the number of physical segments mapped (this may be shorter

than <nents> passed in if the block layer determines that some

elements of the scatter/gather list are physically adjacent and thus

may be mapped with a single entry).

than <nents> passed in if some elements of the scatter/gather list are

physically or virtually adjacent and an IOMMU maps them with a single

entry).



Please note that the sg cannot be mapped again if it has been mapped once.

The mapping process is allowed to destroy information in the sg.