On Wed, Aug 29, 2018 at 07:55:21AM +0200, Christoph Hellwig wrote: > 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). NAK on that at the moment. > 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. Well, as I've no idea what the issue is here, I can't do anything or make any suggestions. I wasn't copied on the initial part of the thread. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 13.8Mbps down 630kbps up According to speedtest.net: 13Mbps down 490kbps up _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
