[Intel-gfx] [PATCH v2 0/2] drm/i915/bxt: work around HW coherency issue

[Chris Wilson]

On Fri, Aug 14, 2015 at 03:38:55PM +0300, Imre Deak wrote:
> This is a v2 of [1]. Since v1 the HW team confirmed that there is an
> HW issue in A steppings with the GPU/CPU snoop logic, which explains why
> we need this workaround.

I've been testing this extensively, and I do believe we can use clflush
for all gen - it is a measurable improvement over using the
heavyweight/locked read of ACTHD, and none of the coherency tests have
thrown any warnings (over a period of a couple of months now).
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre