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@samsung.com 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