From 630bf10e1c30a4275295e419f9269a461212f174 Mon Sep 17 00:00:00 2001
From: LUU HOAI <hoai.luu.ub@renesas.com>
Date: Tue, 26 Apr 2022 09:41:57 +0100
Subject: drm: rcar-du: Fix Alpha blending issue on Gen3
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Git-commit: b7aaa61726cbc7b941007af14a9f991a828c67e4
Patch-mainline: v6.0-rc1
References: jsc#PED-1166 jsc#PED-1168 jsc#PED-1170 jsc#PED-1218 jsc#PED-1220 jsc#PED-1222 jsc#PED-1223 jsc#PED-1225 jsc#PED-2849

As per R-Car-Gen3_Common_OPC_Customer_Notifications_V30.1.pdf,
unexpected image output(such as incorrect colors or planes being
invisible) can happen on the below conditions, as PnALPHAR register
is not initialized by reset.

When alpha blending (PpMRm.PpSPIM=0b101) is performed and:
	•two Planes are enabled on any DUn (n=0,1,2,3)
		oDSPRn= 0x0000 0031 or 0x0000 0013
	•or DU0 and DU1 is used for display at the same time
		oDSPR0= 0x0000 0001 and DSPR1= 0x0000 0003
		oDSPR0= 0x0000 0003 and DSPR1= 0x0000 0001
	•or DU2 and DU3(H3 Only) is used for display at the same time
		oDSPR2= 0x0000 0001 and DSPR3= 0x0000 0003
		oDSPR2= 0x0000 0003 and DSPR3= 0x0000 0001

This patch set PnALPHAR register to 0 to avoid this issue.

Signed-off-by: LUU HOAI <hoai.luu.ub@renesas.com>
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Patrik Jakobsson <pjakobsson@suse.de>
---
 drivers/gpu/drm/rcar-du/rcar_du_plane.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/rcar-du/rcar_du_plane.c b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
index 9a9bc8bcda30..501d79367e3e 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_plane.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
@@ -512,6 +512,18 @@ static void rcar_du_plane_setup_format_gen3(struct rcar_du_group *rgrp,
 
 	rcar_du_plane_write(rgrp, index, PnDDCR4,
 			    state->format->edf | PnDDCR4_CODE);
+
+	/*
+	 * On Gen3, some DU channels have two planes, each being wired to a
+	 * separate VSPD instance. The DU can then blend two planes. While
+	 * this feature isn't used by the driver, issues related to alpha
+	 * blending (such as incorrect colors or planes being invisible) may
+	 * still occur if the PnALPHAR register has a stale value. Set the
+	 * register to 0 to avoid this.
+	 */
+
+	/* TODO: Check if alpha-blending should be disabled in PnMR. */
+	rcar_du_plane_write(rgrp, index, PnALPHAR, 0);
 }
 
 static void rcar_du_plane_setup_format(struct rcar_du_group *rgrp,
-- 
2.38.1