[PATCH v2 03/20] drm/bridge-connector: Attach max bpc for non-HDMI bridges

[Xilin Wu]

Allow non-HDMI bridges to advertise their output bit-depth limit through
max_bpc. Attach the max bpc property when the lowest reported limit in the
chain exceeds 8, ignoring bridges that do not report a limit. This lets
DP drivers expose deep-color support without attaching the property in
their connector initialization code.

Use a lower bound of 6 for DP and eDP, which support 6 bpc RGB output, and
8 for other connector types. Keep the existing HDMI registration path.
The property can be attached before connector state allocation; the
atomic state helper initializes its default when state is created.

Assisted-by: LLM
Signed-off-by: Xilin Wu <sophon@xxxxxxxxx>
---
 drivers/gpu/drm/display/drm_bridge_connector.c | 18 ++++++++++++++++++
 include/drm/drm_bridge.h                       | 11 ++++++++---
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/display/drm_bridge_connector.c b/drivers/gpu/drm/display/drm_bridge_connector.c
index 8b54069fa53a..be2e08a3694a 100644
--- a/drivers/gpu/drm/display/drm_bridge_connector.c
+++ b/drivers/gpu/drm/display/drm_bridge_connector.c
@@ -825,6 +825,7 @@ struct drm_connector *drm_bridge_connector_init(struct drm_device *drm,
 	struct drm_bridge *panel_bridge __free(drm_bridge_put) = NULL;
 	unsigned int supported_formats = BIT(DRM_OUTPUT_COLOR_FORMAT_RGB444);
 	unsigned int max_bpc = 8;
+	unsigned int chain_max_bpc = 0;
 	bool support_hdcp = false;
 	int connector_type;
 	int ret;
@@ -985,6 +986,10 @@ struct drm_connector *drm_bridge_connector_init(struct drm_device *drm,
 			panel_bridge = drm_bridge_get(bridge);
 		}
 
+		if (bridge->max_bpc)
+			chain_max_bpc = chain_max_bpc ?
+				min(chain_max_bpc, bridge->max_bpc) : bridge->max_bpc;
+
 		if (bridge->support_hdcp)
 			support_hdcp = true;
 	}
@@ -1026,6 +1031,19 @@ struct drm_connector *drm_bridge_connector_init(struct drm_device *drm,
 					  connector_type, ddc);
 		if (ret)
 			return ERR_PTR(ret);
+
+		if (chain_max_bpc > 8) {
+			unsigned int min_bpc = 8;
+
+			if (connector_type == DRM_MODE_CONNECTOR_DisplayPort ||
+			    connector_type == DRM_MODE_CONNECTOR_eDP)
+				min_bpc = 6;
+
+			ret = drm_connector_attach_max_bpc_property(connector, min_bpc,
+								    chain_max_bpc);
+			if (ret)
+				return ERR_PTR(ret);
+		}
 	}
 
 	if (bridge_connector->bridge_hdmi_audio ||
diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
index 58fff047f43b..01ad1878149e 100644
--- a/include/drm/drm_bridge.h
+++ b/include/drm/drm_bridge.h
@@ -1089,9 +1089,14 @@ struct drm_bridge {
 	unsigned int supported_formats;
 
 	/**
-	 * @max_bpc: Maximum bits per char the HDMI bridge supports. Allowed
-	 * values are 8, 10 and 12. This is only relevant if
-	 * @DRM_BRIDGE_OP_HDMI is set.
+	 * @max_bpc: Maximum bits per color component the bridge supports.
+	 * Zero means that the bridge does not report a limit. For HDMI bridges
+	 * with @DRM_BRIDGE_OP_HDMI set, allowed values are 8, 10 and 12.
+	 *
+	 * For non-HDMI connectors, drm_bridge_connector_init() attaches the
+	 * max bpc property when the lowest nonzero limit in the bridge chain
+	 * exceeds 8. Bridges remain responsible for validating configurations
+	 * against any limits not reported here.
 	 */
 	unsigned int max_bpc;
 

-- 
2.56.0