On Thu, 24 Jan 2019 at 13:31, Koenig, Christian <Christian.Koenig@xxxxxxx> wrote: > > Am 24.01.19 um 13:06 schrieb Ard Biesheuvel: > > The DRM driver stack is designed to work with cache coherent devices > > only, but permits an optimization to be enabled in some cases, where > > for some buffers, both the CPU and the GPU use uncached mappings, > > removing the need for DMA snooping and allocation in the CPU caches. > > > > The use of uncached GPU mappings relies on the correct implementation > > of the PCIe NoSnoop TLP attribute by the platform, otherwise the GPU > > will use cached mappings nonetheless. On x86 platforms, this does not > > seem to matter, as uncached CPU mappings will snoop the caches in any > > case. However, on ARM and arm64, enabling this optimization on a > > platform where NoSnoop is ignored results in loss of coherency, which > > breaks correct operation of the device. Since we have no way of > > detecting whether NoSnoop works or not, just disable this > > optimization entirely for ARM and arm64. > > > > Cc: Christian Koenig <christian.koenig@xxxxxxx> > > Cc: Alex Deucher <alexander.deucher@xxxxxxx> > > Cc: David Zhou <David1.Zhou@xxxxxxx> > > Cc: Huang Rui <ray.huang@xxxxxxx> > > Cc: Junwei Zhang <Jerry.Zhang@xxxxxxx> > > Cc: Michel Daenzer <michel.daenzer@xxxxxxx> > > Cc: David Airlie <airlied@xxxxxxxx> > > Cc: Daniel Vetter <daniel@xxxxxxxx> > > Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx> > > Cc: Maxime Ripard <maxime.ripard@xxxxxxxxxxx> > > Cc: Sean Paul <sean@xxxxxxxxxx> > > Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> > > Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> > > Cc: Will Deacon <will.deacon@xxxxxxx> > > Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> > > Cc: Robin Murphy <robin.murphy@xxxxxxx> > > Cc: amd-gfx list <amd-gfx@xxxxxxxxxxxxxxxxxxxxx> > > Cc: dri-devel <dri-devel@xxxxxxxxxxxxxxxxxxxxx> > > Reported-by: Carsten Haitzler <Carsten.Haitzler@xxxxxxx> > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > > The subject line should probably read "disable uncached...". > Ugh, of course ... > With that fixed the patch is Reviewed-by: Christian König > <christian.koenig@xxxxxxx>. > Thanks. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
