drm: rcar-du: Cache DSYSR value to ensure known initial value

DSYSR is a DU channel register that also contains group fields. It is
thus written to by both the group and CRTC code, using read-update-write
sequences. As the register isn't initialized explicitly at startup time,
this can lead to invalid or otherwise unexpected values being written to
some of the fields if they have been modified by the firmware or just
not reset properly.

To fix this we can write a fully known value to the DSYSR register when
turning a channel's functional clock on. However, the mix of group and
channel fields complicate this. A simpler solution is to cache the
register and initialize the cached value to the desired hardware
defaults.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>

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

@@ -57,13 +57,12 @@ static void rcar_du_crtc_set(struct rcar_du_crtc *rcrtc, u32 reg, u32 set)
 		      rcar_du_read(rcdu, rcrtc->mmio_offset + reg) | set);
 }
 
-static void rcar_du_crtc_clr_set(struct rcar_du_crtc *rcrtc, u32 reg,
-				 u32 clr, u32 set)
+void rcar_du_crtc_dsysr_clr_set(struct rcar_du_crtc *rcrtc, u32 clr, u32 set)
 {
 	struct rcar_du_device *rcdu = rcrtc->group->dev;
-	u32 value = rcar_du_read(rcdu, rcrtc->mmio_offset + reg);
 
-	rcar_du_write(rcdu, rcrtc->mmio_offset + reg, (value & ~clr) | set);
+	rcrtc->dsysr = (rcrtc->dsysr & ~clr) | set;
+	rcar_du_write(rcdu, rcrtc->mmio_offset + DSYSR, rcrtc->dsysr);
 }
 
 /* -----------------------------------------------------------------------------
@@ -576,9 +575,9 @@ static void rcar_du_crtc_start(struct rcar_du_crtc *rcrtc)
 	 * actively driven).
 	 */
 	interlaced = rcrtc->crtc.mode.flags & DRM_MODE_FLAG_INTERLACE;
-	rcar_du_crtc_clr_set(rcrtc, DSYSR, DSYSR_TVM_MASK | DSYSR_SCM_MASK,
-			     (interlaced ? DSYSR_SCM_INT_VIDEO : 0) |
-			     DSYSR_TVM_MASTER);
+	rcar_du_crtc_dsysr_clr_set(rcrtc, DSYSR_TVM_MASK | DSYSR_SCM_MASK,
+				   (interlaced ? DSYSR_SCM_INT_VIDEO : 0) |
+				   DSYSR_TVM_MASTER);
 
 	rcar_du_group_start_stop(rcrtc->group, true);
 }
@@ -645,7 +644,7 @@ static void rcar_du_crtc_stop(struct rcar_du_crtc *rcrtc)
 	 * Select switch sync mode. This stops display operation and configures
 	 * the HSYNC and VSYNC signals as inputs.
 	 */
-	rcar_du_crtc_clr_set(rcrtc, DSYSR, DSYSR_TVM_MASK, DSYSR_TVM_SWITCH);
+	rcar_du_crtc_dsysr_clr_set(rcrtc, DSYSR_TVM_MASK, DSYSR_TVM_SWITCH);
 
 	rcar_du_group_start_stop(rcrtc->group, false);
 }
@@ -1121,6 +1120,7 @@ int rcar_du_crtc_create(struct rcar_du_group *rgrp, unsigned int swindex,
 	rcrtc->group = rgrp;
 	rcrtc->mmio_offset = mmio_offsets[hwindex];
 	rcrtc->index = hwindex;
+	rcrtc->dsysr = (rcrtc->index % 2 ? 0 : DSYSR_DRES) | DSYSR_TVM_TVSYNC;
 
 	if (rcar_du_has(rcdu, RCAR_DU_FEATURE_VSP1_SOURCE))
 		primary = &rcrtc->vsp->planes[rcrtc->vsp_pipe].plane;

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

@@ -30,6 +30,7 @@ struct rcar_du_vsp;
  * @mmio_offset: offset of the CRTC registers in the DU MMIO block
  * @index: CRTC software and hardware index
  * @initialized: whether the CRTC has been initialized and clocks enabled
+ * @dsysr: cached value of the DSYSR register
  * @vblank_enable: whether vblank events are enabled on this CRTC
  * @event: event to post when the pending page flip completes
  * @flip_wait: wait queue used to signal page flip completion
@@ -50,6 +51,8 @@ struct rcar_du_crtc {
 	unsigned int index;
 	bool initialized;
 
+	u32 dsysr;
+
 	bool vblank_enable;
 	struct drm_pending_vblank_event *event;
 	wait_queue_head_t flip_wait;
@@ -103,4 +106,6 @@ void rcar_du_crtc_route_output(struct drm_crtc *crtc,
 			       enum rcar_du_output output);
 void rcar_du_crtc_finish_page_flip(struct rcar_du_crtc *rcrtc);
 
+void rcar_du_crtc_dsysr_clr_set(struct rcar_du_crtc *rcrtc, u32 clr, u32 set);
+
 #endif /* __RCAR_DU_CRTC_H__ */

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

@@ -202,9 +202,10 @@ void rcar_du_group_put(struct rcar_du_group *rgrp)
 
 static void __rcar_du_group_start_stop(struct rcar_du_group *rgrp, bool start)
 {
-	rcar_du_group_write(rgrp, DSYSR,
-		(rcar_du_group_read(rgrp, DSYSR) & ~(DSYSR_DRES | DSYSR_DEN)) |
-		(start ? DSYSR_DEN : DSYSR_DRES));
+	struct rcar_du_crtc *rcrtc = &rgrp->dev->crtcs[rgrp->index * 2];
+
+	rcar_du_crtc_dsysr_clr_set(rcrtc, DSYSR_DRES | DSYSR_DEN,
+				   start ? DSYSR_DEN : DSYSR_DRES);
 }
 
 void rcar_du_group_start_stop(struct rcar_du_group *rgrp, bool start)