[PATCH RFC v2] drm/bridge: connector: Support the colorspace property for HDMI

["Jan Claußen" <jan.claussen10@web.de>]

Bridge connectors for HDMI do not expose the colorspace property,
so userspace cannot signal the colorimetry (e.g. BT.2020 for HDR).
KWin requires the property before it offers the HDR toggle.

Attach the property for HDMI bridge connectors, next to the other HDMI
properties set up by drmm_connector_hdmi_init().

Force a modeset when the property changes so the new colorimetry
reaches the sink, as vc4 does in its connector atomic_check.

After toggling HDR on, modetest shows that the correct BT.2020 color
space is loaded. After toggling it off, it loads the default color space
again.

Tested in KDE Plasma 6.7.5 on a Radxa Rock 5B (RK3588) with an LG
OLED55B87LC.

Suggested-by: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: Jan Claußen <jan.claussen10@web.de>
---
 .../gpu/drm/display/drm_bridge_connector.c    | 25 ++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/display/drm_bridge_connector.c b/drivers/gpu/drm/display/drm_bridge_connector.c
index 81f3e26f6fdf..885094cc6ddf 100644
--- a/drivers/gpu/drm/display/drm_bridge_connector.c
+++ b/drivers/gpu/drm/display/drm_bridge_connector.c
@@ -414,11 +414,24 @@ static int drm_bridge_connector_atomic_check(struct drm_connector *connector,
 {
 	struct drm_bridge_connector *bridge_connector =
 		to_drm_bridge_connector(connector);
+	struct drm_connector_state *old_state =
+		drm_atomic_get_old_connector_state(state, connector);
+	struct drm_connector_state *new_state =
+		drm_atomic_get_new_connector_state(state, connector);
+	struct drm_crtc_state *crtc_state;
 
-	if (bridge_connector->bridge_hdmi)
-		return drm_atomic_helper_connector_hdmi_check(connector, state);
+	if (!bridge_connector->bridge_hdmi)
+		return 0;
 
-	return 0;
+	if (new_state->crtc && old_state->colorspace != new_state->colorspace) {
+		crtc_state = drm_atomic_get_crtc_state(state, new_state->crtc);
+		if (IS_ERR(crtc_state))
+			return PTR_ERR(crtc_state);
+
+		crtc_state->mode_changed = true;
+	}
+
+	return drm_atomic_helper_connector_hdmi_check(connector, state);
 }
 
 static const struct drm_connector_helper_funcs drm_bridge_connector_helper_funcs = {
@@ -1079,6 +1092,12 @@ struct drm_connector *drm_bridge_connector_init(struct drm_device *drm,
 					       connector_type, ddc);
 		if (ret)
 			return ERR_PTR(ret);
+
+		ret = drm_mode_create_hdmi_colorspace_property(connector, 0);
+		if (ret)
+			return ERR_PTR(ret);
+
+		drm_connector_attach_colorspace_property(connector);
 	} else {
 		ret = drmm_connector_init(drm, connector,
 					  &drm_bridge_connector_funcs,
-- 

Changes in v2:
* Only look up the CRTC state when the connector has a CRTC
* Only apply the check to HDMI bridge connectors
* Move declarations to the top of the function

v1: https://lore.kernel.org/all/20261011132024.2833-1-jan.claussen10@web.de

2.56.0