drm/i915: Add an interface to dynamically change the cache level

[anholt v2: Don't forget that when going from cached to uncached, we
haven't been tracking the write domain from the CPU perspective, since
we haven't needed it for GPU coherency.]

[ickle v3: We also need to make sure we relinquish any fences on older
chipsets and clear the GTT for sane domain tracking.]

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 95c4b14..e961568 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -236,7 +236,8 @@
 		ret = -ENOMEM;
 		goto err;
 	}
-	obj->cache_level = I915_CACHE_LLC;
+
+	i915_gem_object_set_cache_level(obj, I915_CACHE_LLC);
 
 	ret = i915_gem_object_pin(obj, 4096, true);
 	if (ret)
@@ -776,7 +777,8 @@
 		ret = -ENOMEM;
 		goto err;
 	}
-	obj->cache_level = I915_CACHE_LLC;
+
+	i915_gem_object_set_cache_level(obj, I915_CACHE_LLC);
 
 	ret = i915_gem_object_pin(obj, 4096, true);
 	if (ret != 0) {