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Commit e5756c10 authored by Imre Deak's avatar Imre Deak Committed by Daniel Vetter
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drm/i915/bxt: don't allow cached GEM mappings on A stepping 



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: default avatarImre Deak <imre.deak@intel.com>
Reviewed-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
parent 319404df

drivers/gpu/drm/i915/i915_gem.c

+9 −0
Original line number Diff line number Diff line
@@ -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: