[Intel-gfx] [PATCH v3 2/2] drm/i915/bxt: don't allow cached GEM mappings on A stepping

[Chris Wilson]

On Fri, Aug 14, 2015 at 06:43:30PM +0300, Imre Deak wrote:
> 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 at intel.com>

I checked in the two userspaces where I have used snooping that both
handle an error correctly, so

Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre