drm/bridge: lt9611: Fix handling of 4k panels

4k requires two dsi pipes, so don't report MODE_OK when only a
single pipe is configured. But rather report MODE_PANEL to
signal that requirements of the panel are not being met.
Reported-by: Peter Collingbourne <pcc@google.com>
Suggested-by: Peter Collingbourne <pcc@google.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Tested-by: John Stultz <john.stultz@linaro.org>
Tested-by: Anibal Limon <anibal.limon@linaro.org>
Tested-by: Peter Collingbourne <pcc@google.com>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Acked-by: Vinod Koul <vkoul@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201217140933.1133969-1-robert.foss@linaro.org

drivers/gpu/drm/bridge/lontium-lt9611.c

@@ -867,8 +867,14 @@ static enum drm_mode_status lt9611_bridge_mode_valid(struct drm_bridge *bridge,
 						     const struct drm_display_mode *mode)
 {
 	struct lt9611_mode *lt9611_mode = lt9611_find_mode(mode);
+	struct lt9611 *lt9611 = bridge_to_lt9611(bridge);
 
-	return lt9611_mode ? MODE_OK : MODE_BAD;
+	if (!lt9611_mode)
+		return MODE_BAD;
+	else if (lt9611_mode->intfs > 1 && !lt9611->dsi1)
+		return MODE_PANEL;
+	else
+		return MODE_OK;
 }
 
 static void lt9611_bridge_pre_enable(struct drm_bridge *bridge)