Due to a coherency issue on BXT A steppings we can't guarantee a coherent view of cached (CPU snooped) GPU mappings, so fail such requests. User space is supposed to fall back to uncached mappings in this case. v2: - limit the WA to A steppings, on later stepping this HW issue is fixed v3: - return error instead of trying to work around the issue in kernel, since that could confuse user space (Chris) Testcast: igt/gem_store_dword_batches_loop/cached-mapping Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx> --- drivers/gpu/drm/i915/i915_gem.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index 407b6b3..95fd4ff 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -3742,6 +3742,15 @@ int i915_gem_set_caching_ioctl(struct drm_device *dev, void *data, level = I915_CACHE_NONE; break; case I915_CACHING_CACHED: + /* + * Due to a HW issue on BXT A stepping, GPU stores via a + * snooped mapping may leave stale data in a corresponding CPU + * cacheline, whereas normally such cachelines would get + * invalidated. + */ + if (IS_BROXTON(dev) && INTEL_REVID(dev) < BXT_REVID_B0) + return -ENODEV; + level = I915_CACHE_LLC; break; case I915_CACHING_DISPLAY: -- 2.1.4 _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
