dma-fence: remove fill_driver_data callback

Noticed while I was typing docs. Entirely unused.

v2: Remove reference in @timeline_value_str too. While at it clarify
why timeline_value_str has a fence parameter - we don't have an
explicit timeline structure unfortunately.

Cc: Eric Anholt <eric@anholt.net>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Christian König <christian.koenig@amd.com> (v1)
Cc: Christian König <christian.koenig@amd.com> (v1)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180503142603.28513-2-daniel.vetter@ffwll.ch

include/linux/dma-fence.h

@@ -217,17 +217,6 @@ struct dma_fence_ops {
 	 */
 	void (*release)(struct dma_fence *fence);
 
-	/**
-	 * @fill_driver_data:
-	 *
-	 * Callback to fill in free-form debug info.
-	 *
-	 * Returns amount of bytes filled, or negative error on failure.
-	 *
-	 * This callback is optional.
-	 */
-	int (*fill_driver_data)(struct dma_fence *fence, void *data, int size);
-
 	/**
 	 * @fence_value_str:
 	 *
@@ -242,8 +231,9 @@ struct dma_fence_ops {
 	 * @timeline_value_str:
 	 *
 	 * Fills in the current value of the timeline as a string, like the
-	 * sequence number. This should match what @fill_driver_data prints for
+	 * sequence number. Note that the specific fence passed to this function
-	 * the most recently signalled fence (assuming no delayed signalling).
+	 * should not matter, drivers should only use it to look up the
+	 * corresponding timeline structures.
 	 */
 	void (*timeline_value_str)(struct dma_fence *fence,
 				   char *str, int size);