linux-kernel - [PATCH v2 01/10] drm: bridge: dw_hdmi: Disable scrambler feature when not supported

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Message-ID: <20240908132823.3308029-2-jonas@kwiboo.se>
Date: Sun,  8 Sep 2024 13:28:03 +0000
From: Jonas Karlman <jonas@...boo.se>
To: Andrzej Hajda <andrzej.hajda@...el.com>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Robert Foss <rfoss@...nel.org>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
	Jonas Karlman <jonas@...boo.se>,
	Jernej Skrabec <jernej.skrabec@...il.com>
Cc: Christian Hewitt <christianshewitt@...il.com>,
	Diederik de Haas <didi.debian@...ow.org>,
	Christopher Obbard <chris.obbard@...labora.com>,
	dri-devel@...ts.freedesktop.org,
	linux-rockchip@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 01/10] drm: bridge: dw_hdmi: Disable scrambler feature when not supported

The scrambler feature can be left enabled when hotplugging from a sink
and mode that require scrambling to a sink that does not support SCDC or
scrambling.

Typically a blank screen or 'no signal' message can be observed after
using a HDMI 2.0 4K@...z mode and then hotplugging to a sink that only
support HDMI 1.4.

Fix this by disabling the scrambler feature when SCDC is not supported.

Fixes: 264fce6cc2c1 ("drm/bridge: dw-hdmi: Add SCDC and TMDS Scrambling support")
Reported-by: Christopher Obbard <chris.obbard@...labora.com>
Signed-off-by: Jonas Karlman <jonas@...boo.se>
---
v2: New patch
---
 drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
index 0031f3c54882..9e7f86a0bf5c 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
@@ -2117,6 +2117,8 @@ static void hdmi_av_composer(struct dw_hdmi *hdmi,
 				    HDMI_MC_SWRSTZ);
 			drm_scdc_set_scrambling(hdmi->curr_conn, 0);
 		}
+	} else if (hdmi->version >= 0x200a) {
+		hdmi_writeb(hdmi, 0, HDMI_FC_SCRAMBLER_CTRL);
 	}
 
 	/* Set up horizontal active pixel width */
-- 
2.46.0