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authorFUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>2008-12-01 16:14:01 -0500
committerLinus Torvalds <torvalds@linux-foundation.org>2008-12-01 22:55:24 -0500
commit1d678f365dae28420fa7329a2a35390b3582678d (patch)
tree84b6e574a4d913dd2abe59f052b5848424e4ce38
parent4280e3126f641898f0ed1a931645373d3489e2a6 (diff)
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: 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>
-rw-r--r--Documentation/DMA-API.txt8
1 files changed, 3 insertions, 5 deletions
diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
index b8e86460046e..b462bb149543 100644
--- a/Documentation/DMA-API.txt
+++ b/Documentation/DMA-API.txt
@@ -316,12 +316,10 @@ reduce current DMA mapping usage or delay and try again later).
316 pci_map_sg(struct pci_dev *hwdev, struct scatterlist *sg, 316 pci_map_sg(struct pci_dev *hwdev, struct scatterlist *sg,
317 int nents, int direction) 317 int nents, int direction)
318 318
319Maps a scatter gather list from the block layer.
320
321Returns: the number of physical segments mapped (this may be shorter 319Returns: the number of physical segments mapped (this may be shorter
322than <nents> passed in if the block layer determines that some 320than <nents> passed in if some elements of the scatter/gather list are
323elements of the scatter/gather list are physically adjacent and thus 321physically or virtually adjacent and an IOMMU maps them with a single
324may be mapped with a single entry). 322entry).
325 323
326Please note that the sg cannot be mapped again if it has been mapped once. 324Please note that the sg cannot be mapped again if it has been mapped once.
327The mapping process is allowed to destroy information in the sg. 325The mapping process is allowed to destroy information in the sg.