On Tue, Apr 03, 2018 at 08:08:32PM +0200, Daniel Vetter wrote: > I did not mean you should dma_map_sg/page. I just meant that using > dma_map_resource to fill only the dma address part of the sg table seems > perfectly sufficient. But that is not how the interface work, especially facing sg_dma_len. > Assuming you get an sg table that's been mapping by calling dma_map_sg was > always a bit a case of bending the abstraction to avoid typing code. The > only thing an importer ever should have done is look at the dma addresses > in that sg table, nothing else. The scatterlist is not a very good abstraction unfortunately, but it it is spread all over the kernel. And we do expect that anyone who gets passed a scatterlist can use sg_page() or sg_virt() (which calls sg_page()) on it. Your changes would break that, and will cause major trouble because of that. If you want to expose p2p memory returned from dma_map_resource in dmabuf do not use scatterlists for this please, but with a new interface that explicitly passes a virtual address, a dma address and a length and make it very clear that virt_to_page will not work on the virtual address.
