drm/ttm: Add release_notify callback to ttm_bo_driver

This notifies the driver that a BO is about to be released.

Releasing a BO also invokes the move_notify callback from
ttm_bo_cleanup_memtype_use, but that happens too late for anything
that would add fences to the BO and require a delayed delete.
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/ttm/ttm_bo.c

@@ -671,6 +671,9 @@ static void ttm_bo_release(struct kref *kref)
 	struct ttm_bo_device *bdev = bo->bdev;
 	struct ttm_mem_type_manager *man = &bdev->man[bo->mem.mem_type];
 
+	if (bo->bdev->driver->release_notify)
+		bo->bdev->driver->release_notify(bo);
+
 	drm_vma_offset_remove(&bdev->vma_manager, &bo->vma_node);
 	ttm_mem_io_lock(man, false);
 	ttm_mem_io_free_vm(bo);

include/drm/ttm/ttm_bo_driver.h

@@ -390,6 +390,16 @@ struct ttm_bo_driver {
 	 * notify driver that a BO was deleted from LRU.
 	 */
 	void (*del_from_lru_notify)(struct ttm_buffer_object *bo);
+
+	/**
+	 * Notify the driver that we're about to release a BO
+	 *
+	 * @bo: BO that is about to be released
+	 *
+	 * Gives the driver a chance to do any cleanup, including
+	 * adding fences that may force a delayed delete
+	 */
+	void (*release_notify)(struct ttm_buffer_object *bo);
 };
 
 /**