On Tue, Aug 28, 2018 at 03:14:14PM +0100, Russell King - ARM Linux wrote: > But yes, the fundamental fact is that AMBA devices don't have any > care about the differences between coherent and streaming DMA. The > distinction that we make in the kernel is purely a software one when > it comes to these devices. > > Most AMBA devices themselves are not DMA capable, as they are only > connected to the APB (Amba peripheral bus) and they rely on a > separate DMA engine for their DMA. APB devices should not have DMA > masks - their DMA capabilities are entirely down to the DMA controller. > So, the majority of AMBA devices should not have any DMA masks. > > Only those connected to a bus that they can master on (eg AXI) should > have DMA masks - things like the PL08x DMA controllers, PL11x LCD > controllers, etc. As I've said above, there is no difference between > streaming and coherent DMA for these devices. So for now I plan to apply the patch from Linus to just set a dma mask, as that gets back the previous behavior where dma did just work (as it did without a mask). But if Linus, you or someone else familiar with amba would like to add an explicit opt-in into dma support eventually that would be even better. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
