[Intel-gfx] [PATCH 17/30] drm/i915: Do not clflush snooped objects

[Chris Wilson]

Rely on the GPU snooping into the CPU cache for appropriately bound
objects on MI_FLUSH. Or perhaps one day we will have a cache-coherent
CPU/GPU package...

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Eric Anholt <eric at anholt.net>
---
 drivers/gpu/drm/i915/i915_gem.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 264bec8..fa483d8 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2878,6 +2878,14 @@ i915_gem_clflush_object(struct drm_i915_gem_object *obj)
 	if (obj->pages == NULL)
 		return;
 
+	/* If the GPU is snooping the contents of the CPU cache,
+	 * we do not need to clear the CPU cache lines. Instead we need
+	 * to be sure to flush/invalidate the RENDER cache when the contents
+	 * must be refreshed.
+	 */
+	if (obj->cache_level != I915_CACHE_NONE)
+		return;
+
 	trace_i915_gem_object_clflush(obj);
 
 	drm_clflush_pages(obj->pages, obj->base.size / PAGE_SIZE);
-- 
1.7.4.1