[Intel-gfx] [PATCH 02/13] 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>
Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/gpu/drm/i915/i915_gem.c |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 264bec8..bf32527 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2878,6 +2878,17 @@ 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 manually clear the CPU cache lines.  However,
+	 * the caches are only snooped when the render cache is
+	 * flushed/invalidated.  As we always have to emit invalidations
+	 * and flushes when moving into and out of the RENDER domain, correct
+	 * snooping behaviour occurs naturally as the result of our domain
+	 * tracking.
+	 */
+	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