[PATCH v4 01/17] drm: bridge: dw_hdmi: Disable scrambler feature when not supported

Jonas Karlman
2026-05-04T19:11:37Z

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@60Hz 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@collabora.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
---
v4: No change
v3: Collect r-b tag
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 f4a1ebb79716..248454c45d6b 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
@@ -2135,6 +2135,8 @@ 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 */
--
2.54.0