linux-kernel - [PATCH v1 3/5] drm: bridge: dw_hdmi: Enable GCP only for Deep Color

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Date:   Wed,  6 Apr 2022 16:48:35 +0800
From:   Sandor.yu@....com
To:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        andrzej.hajda@...el.com, narmstrong@...libre.com,
        robert.foss@...aro.org, Laurent.pinchart@...asonboard.com,
        jonas@...boo.se, jernej.skrabec@...il.com
Cc:     Sandor.yu@....com, shengjiu.wang@....com, cai.huoqing@...ux.dev,
        maxime@...no.tech, harry.wentland@....com,
        hverkuil-cisco@...all.nl, amuel@...lland.org
Subject: [PATCH v1 3/5] drm: bridge: dw_hdmi: Enable GCP only for Deep Color

From: Sandor Yu <Sandor.yu@....com>

HDMI1.4b specification section 6.5.3:
Source shall only send GCPs with non-zero CD to sinks
that indicate support for Deep Color.

DW HDMI GPC default enabled, clear gpc_auto bit for bpp 24.

Signed-off-by: Sandor Yu <Sandor.yu@....com>
---
 drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
index b11577de4836..c7b11582529e 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
@@ -1160,6 +1160,14 @@ static void hdmi_video_packetize(struct dw_hdmi *hdmi)
 		HDMI_VP_PR_CD_DESIRED_PR_FACTOR_MASK);
 	hdmi_writeb(hdmi, val, HDMI_VP_PR_CD);
 
+	val = hdmi_readb(hdmi, HDMI_FC_DATAUTO3);
+	if (color_depth == 4)
+		/* disable Auto GCP when bpp 24 */
+		val &= ~0x4;
+	else
+		val |= 0x4;
+	hdmi_writeb(hdmi, val, HDMI_FC_DATAUTO3);
+
 	hdmi_modb(hdmi, HDMI_VP_STUFF_PR_STUFFING_STUFFING_MODE,
 		  HDMI_VP_STUFF_PR_STUFFING_MASK, HDMI_VP_STUFF);
 
-- 
2.25.1