[PATCH v5 2/7] drm/rcar-du: Write DPTSR only if the second source exists

[Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>]

From: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>

Currently the driver always writes DPTSR when setting up the hardware.
However, writing the register is only meaningful when the second source
for a plane is used, and the register is not even documented for SoCs
that do not have the second source.

So move the write behind a condition.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com> # On R-Car M3-N
---
 drivers/gpu/drm/renesas/rcar-du/rcar_du_group.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/renesas/rcar-du/rcar_du_group.c b/drivers/gpu/drm/renesas/rcar-du/rcar_du_group.c
index 2ccd2581f544..1ec806c8e013 100644
--- a/drivers/gpu/drm/renesas/rcar-du/rcar_du_group.c
+++ b/drivers/gpu/drm/renesas/rcar-du/rcar_du_group.c
@@ -185,11 +185,21 @@ static void rcar_du_group_setup(struct rcar_du_group *rgrp)
 		dorcr |= DORCR_PG1T | DORCR_DK1S | DORCR_PG1D_DS1;
 	rcar_du_group_write(rgrp, DORCR, dorcr);
 
-	/* Apply planes to CRTCs association. */
-	mutex_lock(&rgrp->lock);
-	rcar_du_group_write(rgrp, DPTSR, (rgrp->dptsr_planes << 16) |
-			    rgrp->dptsr_planes);
-	mutex_unlock(&rgrp->lock);
+	/*
+	 * DPTSR is used to select the source for the planes of a group. The
+	 * first source is chosen by writing 0 to the respective bits, and this
+	 * is always the default value of the register. In other words, writing
+	 * DPTSR is only needed if the SoC supports choosing the second source.
+	 *
+	 * The SoCs documentations seems to confirm this, as the DPTSR register
+	 * is not documented if only the first source exists on that SoC.
+	 */
+	if (rgrp->channels_mask & BIT(1)) {
+		mutex_lock(&rgrp->lock);
+		rcar_du_group_write(rgrp, DPTSR, (rgrp->dptsr_planes << 16) |
+				    rgrp->dptsr_planes);
+		mutex_unlock(&rgrp->lock);
+	}
 }
 
 /*

-- 
2.43.0