On Thu, Nov 29, 2018 at 03:43:50PM +0100, Daniel Vetter wrote: > Yeah we had patches to add manual cache management code to drm, so we > don't have to abuse the dma streaming api anymore. Got shouted down. > Abusing the dma streaming api also gets shouted down. It's a gpu, any > idea of these drivers actually being platform independent is out of > the window from the start anyway, so we're ok with tying this to > platforms. Manual or not the iommu API is missing APIs for cache management, which makes it kinda surprising it actually ever worked for non-coherent devices. And fortunately while some people spent the last year ot two bickering about the situation others actually did work, and we now have a generic arch_sync_dma_for_device/arch_sync_dma_for_cpu kernel-internal API. This is only used for DMA API internals so far, and explicitly not intended for direct driver use, but it would be perfect as the backend for iommu API cache maintainance functions. It exists on all but two architectures on mainline. Out of those powerpc is in the works, only arm32 will need some major help.
