drm/ttm: Introduce ttm_bo_get() and ttm_bo_put() for ref counting

The TTM buffer-object interface provides ttm_bo_reference() and
ttm_bo_unref() for managing reference counts. Replacing them with
ttm_bo_get() and ttm_bo_put() aligns the API with conventions used
throughout the Linux kernel.

The implementation of ttm_bo_unref() clears the supplied pointer
to NULL. This leads to workarounds where the caller saves the
pointer's value before de-referencing the BO. ttm_bo_put() does
not clear the supplied pointer.

Signed-off-by: Thomas Zimmermann <contact@tzimmermann.org>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/ttm/ttm_bo.c

@@ -587,12 +587,18 @@ static void ttm_bo_release(struct kref *kref)
 	kref_put(&bo->list_kref, ttm_bo_release_list);
 }
 
+void ttm_bo_put(struct ttm_buffer_object *bo)
+{
+	kref_put(&bo->kref, ttm_bo_release);
+}
+EXPORT_SYMBOL(ttm_bo_put);
+
 void ttm_bo_unref(struct ttm_buffer_object **p_bo)
 {
 	struct ttm_buffer_object *bo = *p_bo;
 
 	*p_bo = NULL;
-	kref_put(&bo->kref, ttm_bo_release);
+	ttm_bo_put(bo);
 }
 EXPORT_SYMBOL(ttm_bo_unref);
 

include/drm/ttm/ttm_bo_api.h

@@ -283,18 +283,30 @@ struct ttm_operation_ctx {
 /* when serving page fault or suspend, allow alloc anyway */
 #define TTM_OPT_FLAG_FORCE_ALLOC		0x2
 
+/**
+ * ttm_bo_get - reference a struct ttm_buffer_object
+ *
+ * @bo: The buffer object.
+ */
+static inline void ttm_bo_get(struct ttm_buffer_object *bo)
+{
+	kref_get(&bo->kref);
+}
+
 /**
  * ttm_bo_reference - reference a struct ttm_buffer_object
  *
  * @bo: The buffer object.
  *
  * Returns a refcounted pointer to a buffer object.
+ *
+ * This function is deprecated. Use @ttm_bo_get instead.
  */
 
 static inline struct ttm_buffer_object *
 ttm_bo_reference(struct ttm_buffer_object *bo)
 {
-	kref_get(&bo->kref);
+	ttm_bo_get(bo);
 	return bo;
 }
 
@@ -345,12 +357,23 @@ int ttm_bo_validate(struct ttm_buffer_object *bo,
 		    struct ttm_placement *placement,
 		    struct ttm_operation_ctx *ctx);
 
+/**
+ * ttm_bo_put
+ *
+ * @bo: The buffer object.
+ *
+ * Unreference a buffer object.
+ */
+void ttm_bo_put(struct ttm_buffer_object *bo);
+
 /**
  * ttm_bo_unref
  *
  * @bo: The buffer object.
  *
  * Unreference and clear a pointer to a buffer object.
+ *
+ * This function is deprecated. Use @ttm_bo_put instead.
  */
 void ttm_bo_unref(struct ttm_buffer_object **bo);