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DMA-API.txt: fix description of pci_map_sg/dma_map_sg scatterlists handling

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- 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: FUJITA 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
FUJITA Tomonori 2008-12-01 13:14:01 -08:00 committed by Linus Torvalds
parent 4280e3126f
commit 1d678f365d
1 changed files with 3 additions and 5 deletions
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8
Documentation/DMA-API.txt
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@ -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, pci_map_sg(struct pci_dev *hwdev, struct scatterlist *sg,
int nents, int direction) int nents, int direction)
Maps a scatter gather list from the block layer.
Returns: the number of physical segments mapped (this may be shorter Returns: the number of physical segments mapped (this may be shorter
than <nents> passed in if the block layer determines that some than <nents> passed in if some elements of the scatter/gather list are
elements of the scatter/gather list are physically adjacent and thus physically or virtually adjacent and an IOMMU maps them with a single
may be mapped with a single entry). entry).
Please note that the sg cannot be mapped again if it has been mapped once. 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. The mapping process is allowed to destroy information in the sg.