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...". With that fixed the patch is Reviewed-by: Christian König <christian.koenig@xxxxxxx>. Regards, Christian. > --- > include/drm/drm_cache.h | 18 ++++++++++++++++++ > 1 file changed, 18 insertions(+) > > diff --git a/include/drm/drm_cache.h b/include/drm/drm_cache.h > index bfe1639df02d..97fc498dc767 100644 > --- a/include/drm/drm_cache.h > +++ b/include/drm/drm_cache.h > @@ -47,6 +47,24 @@ static inline bool drm_arch_can_wc_memory(void) > return false; > #elif defined(CONFIG_MIPS) && defined(CONFIG_CPU_LOONGSON3) > return false; > +#elif defined(CONFIG_ARM) || defined(CONFIG_ARM64) > + /* > + * 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. > + */ > + return false; > #else > return true; > #endif _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
