[PATCH v6 01/22] drm: bridge: dw_hdmi: Disable scrambler feature when not supported

[Jonas Karlman]

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@xxxxxxxxxxxxx>
Reviewed-by: Neil Armstrong <neil.armstrong@xxxxxxxxxx>
Tested-by: Diederik de Haas <diederik@xxxxxxxxxxxxxx>  # Rock64, RockPro64, Quartz64-B
Signed-off-by: Jonas Karlman <jonas@xxxxxxxxx>
---
v6: Collect t-b tag
v5: No change
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 41b3a9cfa2f5..d3e6a6562870 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