From 1d678f365dae28420fa7329a2a35390b3582678d Mon Sep 17 00:00:00 2001 From: FUJITA Tomonori Date: Mon, 1 Dec 2008 13:14:01 -0800 Subject: [PATCH] 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 Cc: James Bottomley Cc: Tejun Heo Cc: Jens Axboe Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/DMA-API.txt | 8 +++----- 1 file 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 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 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.