drm/vram-helpers: Set plane fence for display update

Calling the VRAM helper's prepare_fb() helper now sets the plane's
fence object. This will be useful for PRIME support. VRAM helpers
don't support buffer sharing ATM, so for now there are no drivers
requiring this change.

v2:
	* removed a TODO comment about buffer synchronization
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200331092740.29282-1-tzimmermann@suse.de

drivers/gpu/drm/drm_gem_vram_helper.c

@@ -5,6 +5,7 @@
 #include <drm/drm_drv.h>
 #include <drm/drm_file.h>
 #include <drm/drm_framebuffer.h>
+#include <drm/drm_gem_framebuffer_helper.h>
 #include <drm/drm_gem_ttm_helper.h>
 #include <drm/drm_gem_vram_helper.h>
 #include <drm/drm_mode.h>
@@ -670,9 +671,9 @@ EXPORT_SYMBOL(drm_gem_vram_driver_dumb_mmap_offset);
  * @plane:	a DRM plane
  * @new_state:	the plane's new state
  *
- * During plane updates, this function pins the GEM VRAM
- * objects of the plane's new framebuffer to VRAM. Call
- * drm_gem_vram_plane_helper_cleanup_fb() to unpin them.
+ * During plane updates, this function sets the plane's fence and
+ * pins the GEM VRAM objects of the plane's new framebuffer to VRAM.
+ * Call drm_gem_vram_plane_helper_cleanup_fb() to unpin them.
  *
  * Returns:
  *	0 on success, or
@@ -698,6 +699,10 @@ drm_gem_vram_plane_helper_prepare_fb(struct drm_plane *plane,
 			goto err_drm_gem_vram_unpin;
 	}
 
+	ret = drm_gem_fb_prepare_fb(plane, new_state);
+	if (ret)
+		goto err_drm_gem_vram_unpin;
+
 	return 0;
 
 err_drm_gem_vram_unpin: