On Tue, Feb 3, 2015 at 2:48 AM, Daniel Vetter <daniel@xxxxxxxx> wrote: > On Mon, Feb 02, 2015 at 03:30:21PM -0500, Rob Clark wrote: >> On Mon, Feb 2, 2015 at 11:54 AM, Daniel Vetter <daniel@xxxxxxxx> wrote: >> >> My initial thought is for dma-buf to not try to prevent something than >> >> an exporter can actually do.. I think the scenario you describe could >> >> be handled by two sg-lists, if the exporter was clever enough. >> > >> > That's already needed, each attachment has it's own sg-list. After all >> > there's no array of dma_addr_t in the sg tables, so you can't use one sg >> > for more than one mapping. And due to different iommu different devices >> > can easily end up with different addresses. >> >> >> Well, to be fair it may not be explicitly stated, but currently one >> should assume the dma_addr_t's in the dmabuf sglist are bogus. With >> gpu's that implement per-process/context page tables, I'm not really >> sure that there is a sane way to actually do anything else.. > > Hm, what does per-process/context page tables have to do here? At least on > i915 we have a two levels of page tables: > - first level for vm/device isolation, used through dma api > - 2nd level for per-gpu-context isolation and context switching, handled > internally. > > Since atm the dma api doesn't have any context of contexts or different > pagetables, I don't see who you could use that at all. Since I'm stuck w/ an iommu, instead of built in mmu, my plan was to drop use of dma-mapping entirely (incl the current call to dma_map_sg, which I just need until we can use drm_cflush on arm), and attach/detach iommu domains directly to implement context switches. At that point, dma_addr_t really has no sensible meaning for me. BR, -R > -Daniel > -- > Daniel Vetter > Software Engineer, Intel Corporation > +41 (0) 79 365 57 48 - http://blog.ffwll.ch -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>