drm/i915: Zap the GTT mapping when transitioning from untiled to tiled.

As of 52dc7d32, we could leave an old
linear GTT mapping in place, so that apps trying to GTT-mapped write in
tiled data wouldn't get the fence added, and garbage would get displayed.
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_drv.h

@@ -673,6 +673,7 @@ void i915_gem_free_object(struct drm_gem_object *obj);
 int i915_gem_object_pin(struct drm_gem_object *obj, uint32_t alignment);
 void i915_gem_object_unpin(struct drm_gem_object *obj);
 int i915_gem_object_unbind(struct drm_gem_object *obj);
+void i915_gem_release_mmap(struct drm_gem_object *obj);
 void i915_gem_lastclose(struct drm_device *dev);
 uint32_t i915_get_gem_seqno(struct drm_device *dev);
 int i915_gem_object_get_fence_reg(struct drm_gem_object *obj);

drivers/gpu/drm/i915/i915_gem.c

@@ -1266,7 +1266,7 @@ i915_gem_create_mmap_offset(struct drm_gem_object *obj)
  * mapping will then trigger a page fault on the next user access, allowing
  * fixup by i915_gem_fault().
  */
-static void
+void
 i915_gem_release_mmap(struct drm_gem_object *obj)
 {
 	struct drm_device *dev = obj->dev;

drivers/gpu/drm/i915/i915_gem_tiling.c

@@ -521,6 +521,12 @@ i915_gem_set_tiling(struct drm_device *dev, void *data,
 			goto err;
 		}
 
+		/* If we've changed tiling, GTT-mappings of the object
+		 * need to re-fault to ensure that the correct fence register
+		 * setup is in place.
+		 */
+		i915_gem_release_mmap(obj);
+
 		obj_priv->tiling_mode = args->tiling_mode;
 		obj_priv->stride = args->stride;
 	}