Hello,
On 10/26/2012 6:24 PM, Pawel Osciak wrote:
Hi Tomasz,
On Wed, Oct 10, 2012 at 7:46 AM, Tomasz Stanislawski
<t.stanislaws@xxxxxxxxxxx> wrote:
This patch introduces usage of dma_map_sg to map memory behind
a userspace pointer to a device as dma-contiguous mapping.
Perhaps I'm missing something, but I don't understand the purpose of
this patch. If the device can do DMA SG, why use videobuf2-dma-contig
and not videobuf2-dma-sg?
This patch is for devices which doesn't do DMA SG, but might be behind
IOMMU. In such case one can call dma_map_sg() with scatterlist of
individual pages gathered from user pointer (anonymous memory of the
process) which in turn will be mapped into contiguous dma adress space
(dma_map_sg() returns only one chunk in such case). This is not very
intuitive, but it was best way to fit such case into existing
dma-mapping design.
What would be the difference design-wise
between them if this patch is merged?
Best regards
--
Marek Szyprowski
Samsung Poland R&D Center
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