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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: Imre Deak <imre.deak@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This commit is contained in:
Imre Deak 2015-08-14 18:43:30 +03:00 committed by Daniel Vetter
parent 319404df2f
commit e5756c10d8
1 changed files with 9 additions and 0 deletions
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9
drivers/gpu/drm/i915/i915_gem.c
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@ -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: