drm/i915: Avoid nesting of domain changes when setting display plane

Nesting domain changes will cause confusion when trying to interpret the
tracepoints describing the sequence of changes for the object, as well
as obscuring the order of operations for the reader of the code.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NEric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_gem.c

@@ -2914,18 +2914,16 @@ i915_gem_object_set_to_display_plane(struct drm_gem_object *obj)
 			return ret;
 	}
 
+	i915_gem_object_flush_cpu_write_domain(obj);
+
 	old_write_domain = obj->write_domain;
 	old_read_domains = obj->read_domains;
 
-	obj->read_domains &= I915_GEM_DOMAIN_GTT;
-
-	i915_gem_object_flush_cpu_write_domain(obj);
-
 	/* It should now be out of any other write domains, and we can update
 	 * the domain values for our changes.
 	 */
 	BUG_ON((obj->write_domain & ~I915_GEM_DOMAIN_GTT) != 0);
-	obj->read_domains |= I915_GEM_DOMAIN_GTT;
+	obj->read_domains = I915_GEM_DOMAIN_GTT;
 	obj->write_domain = I915_GEM_DOMAIN_GTT;
 	obj_priv->dirty = 1;