Hi Xilin,
On 10/9/2026 11:15 AM, Xilin Wu wrote:
> 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 <[email protected]>
> ---
> 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;
> +
The check on chain_max_bpc here doesn't seem to make any sense.
> 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;
>
>
--
Best,
Chaoyi
