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>
diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
index b8e8646..b462bb1 100644
--- a/Documentation/DMA-API.txt
+++ b/Documentation/DMA-API.txt
@@ -316,12 +316,10 @@
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.