On Thu, 24 Jan 2019 at 15:01, Alex Deucher alexdeucher@gmail.com wrote:
On Thu, Jan 24, 2019 at 9:00 AM Ard Biesheuvel ard.biesheuvel@linaro.org wrote:
On Thu, 24 Jan 2019 at 13:31, Koenig, Christian Christian.Koenig@amd.com 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@amd.com Cc: Alex Deucher alexander.deucher@amd.com Cc: David Zhou David1.Zhou@amd.com Cc: Huang Rui ray.huang@amd.com Cc: Junwei Zhang Jerry.Zhang@amd.com Cc: Michel Daenzer michel.daenzer@amd.com Cc: David Airlie airlied@linux.ie Cc: Daniel Vetter daniel@ffwll.ch Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Maxime Ripard maxime.ripard@bootlin.com Cc: Sean Paul sean@poorly.run Cc: Michael Ellerman mpe@ellerman.id.au Cc: Benjamin Herrenschmidt benh@kernel.crashing.org Cc: Will Deacon will.deacon@arm.com Cc: Christoph Hellwig hch@infradead.org Cc: Robin Murphy robin.murphy@arm.com Cc: amd-gfx list amd-gfx@lists.freedesktop.org Cc: dri-devel dri-devel@lists.freedesktop.org Reported-by: Carsten Haitzler Carsten.Haitzler@arm.com Signed-off-by: Ard Biesheuvel ard.biesheuvel@linaro.org
The subject line should probably read "disable uncached...".
Ugh, of course ...
With that fixed the patch is Reviewed-by: Christian König christian.koenig@amd.com.
Same: Reviewed-by: Alex Deucher alexander.deucher@amd.com
Thanks all
Should I resend the patch with the subject corrected?