Messages in this thread Patch in this message | | | Date | Wed, 19 Nov 2008 16:58:30 +0900 | Subject | Re: pci_map_sg() does not coalesce adjacent physical memory? x86 | From | FUJITA Tomonori <> |
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On Wed, 19 Nov 2008 15:58:12 +0900 FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> wrote:
> On Wed, 19 Nov 2008 07:22:31 +0100 > "Leon Woestenberg" <leon.woestenberg@gmail.com> wrote: > > > Hello, > > > > On Wed, Nov 19, 2008 at 6:19 AM, FUJITA Tomonori > > <fujita.tomonori@lab.ntt.co.jp> wrote: > > > On Mon, 17 Nov 2008 19:15:32 -0800 > > >> > pci_map_sg() does not coalesce the scattergather list for me on x86. > > >> [ Marked as Bogus Report ] > > >> > > >> > Is this expected? Documentation mentions that coalescing is typically > > >> > done by pci_map_sg(). > > > > > > Hm, what document did you read? We might need to fix it. > > > > > http://lxr.linux.no/linux+v2.6.27.6/Documentation/DMA-API.txt > > > > 316 pci_map_sg(struct pci_dev *hwdev, struct scatterlist *sg, > > 317 int nents, int direction) > > 318 > > 319Maps a scatter gather list from the block layer. > > 320 > > 321Returns: the number of physical segments mapped (this may be shorter > > 322than <nents> passed in if the block layer determines that some > > 323elements of the scatter/gather list are physically adjacent and thus > > 324may be mapped with a single entry). > > Hmm, the description looks confusing. The block layer coalesces > physically adjacent entries before pci_map_sg(). pci_map_sg() could > coalesces physically or virtually adjacent entries.
How about this?
= From: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> Subject: [PATCH] fix pci_map_sg/dma_map_sg scatterlists handling in DMA-API.txt
- 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> --- Documentation/DMA-API.txt | 8 +++----- 1 files changed, 3 insertions(+), 5 deletions(-)
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 @@ 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. -- 1.5.5.GIT
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