drm: rcar-du: Restart the DU group when a plane source changes

Plane sources are configured by the VSPS bit in the PnDDCR4 register.
Although the datasheet states that the bit is updated during vertical
blanking, it seems that updates only occur when the DU group is held in
reset through the DSYSR.DRES bit. Restart the group if the source
changes.

Signed-off-by: Laurent Pinchart <[e-mail]>

drivers/gpu/drm/rcar-du/rcar_du_crtc.c

···
 			rcar_du_group_restart(rcrtc->group);
 	}
 
+	/* Restart the group if plane sources have changed. */
+	if (rcrtc->group->need_restart)
+		rcar_du_group_restart(rcrtc->group);
+
 	mutex_unlock(&rcrtc->group->lock);
 
 	rcar_du_group_write(rcrtc->group, rcrtc->index % 2 ? DS2PR : DS1PR,

drivers/gpu/drm/rcar-du/rcar_du_group.c

···
 
 void rcar_du_group_restart(struct rcar_du_group *rgrp)
 {
+	rgrp->need_restart = false;
+
 	__rcar_du_group_start_stop(rgrp, false);
 	__rcar_du_group_start_stop(rgrp, true);
 }

drivers/gpu/drm/rcar-du/rcar_du_group.h

···
  * @dptsr_planes: bitmask of planes driven by dot-clock and timing generator 1
  * @num_planes: number of planes in the group
  * @planes: planes handled by the group
+ * @need_restart: the group needs to be restarted due to a configuration change
  */
 struct rcar_du_group {
 	struct rcar_du_device *dev;
···
 
 	unsigned int num_planes;
 	struct rcar_du_plane planes[RCAR_DU_NUM_KMS_PLANES];
+	bool need_restart;
 };
 
 u32 rcar_du_group_read(struct rcar_du_group *rgrp, u32 reg);

drivers/gpu/drm/rcar-du/rcar_du_plane.c

···
 					struct drm_plane_state *old_state)
 {
 	struct rcar_du_plane *rplane = to_rcar_plane(plane);
+	struct rcar_du_plane_state *old_rstate;
+	struct rcar_du_plane_state *new_rstate;
 
-	if (plane->state->crtc)
-		rcar_du_plane_setup(rplane);
+	if (!plane->state->crtc)
+		return;
+
+	rcar_du_plane_setup(rplane);
+
+	/* Check whether the source has changed from memory to live source or
+	 * from live source to memory. The source has been configured by the
+	 * VSPS bit in the PnDDCR4 register. Although the datasheet states that
+	 * the bit is updated during vertical blanking, it seems that updates
+	 * only occur when the DU group is held in reset through the DSYSR.DRES
+	 * bit. We thus need to restart the group if the source changes.
+	 */
+	old_rstate = to_rcar_plane_state(old_state);
+	new_rstate = to_rcar_plane_state(plane->state);
+
+	if ((old_rstate->source == RCAR_DU_PLANE_MEMORY) !=
+	    (new_rstate->source == RCAR_DU_PLANE_MEMORY))
+		rplane->group->need_restart = true;
 }
 
 static const struct drm_plane_helper_funcs rcar_du_plane_helper_funcs = {