drm/ttm: add lru notify to bo driver v2

allow driver do somethings when lru changed.
v2:
address Michel's comments.
Signed-off-by: Chunming Zhou <david1.zhou@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

@@ -198,19 +198,22 @@ static void ttm_bo_ref_bug(struct kref *list_kref)
 
 void ttm_bo_del_from_lru(struct ttm_buffer_object *bo)
 {
+	struct ttm_bo_device *bdev = bo->bdev;
+	bool notify = false;
+
 	if (!list_empty(&bo->swap)) {
 		list_del_init(&bo->swap);
 		kref_put(&bo->list_kref, ttm_bo_ref_bug);
+		notify = true;
 	}
 	if (!list_empty(&bo->lru)) {
 		list_del_init(&bo->lru);
 		kref_put(&bo->list_kref, ttm_bo_ref_bug);
+		notify = true;
 	}
 
-	/*
-	 * TODO: Add a driver hook to delete from
-	 * driver-specific LRU's here.
-	 */
+	if (notify && bdev->driver->del_from_lru_notify)
+		bdev->driver->del_from_lru_notify(bo);
 }
 
 void ttm_bo_del_sub_from_lru(struct ttm_buffer_object *bo)

include/drm/ttm/ttm_bo_driver.h

@@ -381,6 +381,15 @@ struct ttm_bo_driver {
 	 */
 	int (*access_memory)(struct ttm_buffer_object *bo, unsigned long offset,
 			     void *buf, int len, int write);
+
+	/**
+	 * struct ttm_bo_driver member del_from_lru_notify
+	 *
+	 * @bo: the buffer object deleted from lru
+	 *
+	 * notify driver that a BO was deleted from LRU.
+	 */
+	void (*del_from_lru_notify)(struct ttm_buffer_object *bo);
 };
 
 /**