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authorFUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>2008-12-01 13:14:01 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2008-12-01 19:55:24 -0800
commit1d678f365dae28420fa7329a2a35390b3582678d (patch)
tree84b6e574a4d913dd2abe59f052b5848424e4ce38
parent4280e3126f641898f0ed1a931645373d3489e2a6 (diff)
downloadlinux-2.6.38-lt-ux500-1d678f365dae28420fa7329a2a35390b3582678d.tar.gz
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 b8e86460046..b462bb14954 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).
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.