dma-buf: clarify dma_fence_ops->wait documentation

This callback is pretty much deprecated and should not be used by new implementations.

Clarify that in the documentation as well.
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210901120240.7339-2-christian.koenig@amd.com

include/linux/dma-fence.h

@@ -214,19 +214,15 @@ struct dma_fence_ops {
 	 * Custom wait implementation, defaults to dma_fence_default_wait() if
 	 * not set.
 	 *
-	 * The dma_fence_default_wait implementation should work for any fence, as long
-	 * as @enable_signaling works correctly. This hook allows drivers to
-	 * have an optimized version for the case where a process context is
-	 * already available, e.g. if @enable_signaling for the general case
-	 * needs to set up a worker thread.
+	 * Deprecated and should not be used by new implementations. Only used
+	 * by existing implementations which need special handling for their
+	 * hardware reset procedure.
 	 *
 	 * Must return -ERESTARTSYS if the wait is intr = true and the wait was
 	 * interrupted, and remaining jiffies if fence has signaled, or 0 if wait
 	 * timed out. Can also return other error values on custom implementations,
 	 * which should be treated as if the fence is signaled. For example a hardware
 	 * lockup could be reported like that.
-	 *
-	 * This callback is optional.
 	 */
 	signed long (*wait)(struct dma_fence *fence,
 			    bool intr, signed long timeout);