Not all architectures guarantee that uncached read will flush the write combining buffer. So marking it explicitly is recommended [1].
However we know the architecture we are operating on and can avoid wmb as the UC store will flush the wcb [2]. Omit the wmb() on gen6_ppgtt_invalidate as redundant. References: http://yarchive.net/comp/linux/write_combining.html [1] References: http://download.intel.com/design/PentiumII/applnots/24442201.pdf [2] Cc: Chris Wilson <ch...@chris-wilson.co.uk> Cc: Matthew Auld <matthew.a...@intel.com> Signed-off-by: Mika Kuoppala <mika.kuopp...@linux.intel.com> --- drivers/gpu/drm/i915/i915_gem_gtt.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c index dcac8bd604ab..ef2727f4b6a6 100644 --- a/drivers/gpu/drm/i915/i915_gem_gtt.c +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c @@ -125,10 +125,7 @@ static void gen6_ppgtt_invalidate(struct i915_address_space * const vm) static void gen6_ggtt_invalidate(struct drm_i915_private *dev_priv) { - /* Flush write combining buffer */ - wmb(); - - /* Note that as an uncached mmio write, this should flush the + /* Note that as an uncached mmio write, this will flush the * WCB of the writes into the GGTT before it triggers the invalidate. */ I915_WRITE(GFX_FLSH_CNTL_GEN6, GFX_FLSH_CNTL_EN); -- 2.14.1 _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
