The dw-dp bridge already filters candidate output formats on conn_state->max_bpc in dw_dp_bridge_atomic_get_output_bus_fmts() and validates the result against the link bandwidth, but the connector never exposes the "max bpc" property, so userspace cannot limit the bit depth. Attach the property with a range of 6 to 10, matching dw_dp_output_formats[]: the smallest entry is 6 bpc RGB and the deepest entries are 10 bpc.
drm_connector_attach_max_bpc_property() initializes connector->state->max_requested_bpc and therefore requires the connector to have a state. Rockchip binds its components before drm_mode_config_reset() runs, so the freshly created bridge connector does not have one yet - create the connector state before attaching the property, exactly like drmm_connector_hdmi_init() does for HDMI bridge connectors. The later drm_mode_config_reset() then re-creates the connector state, and the preceding patch makes drm_bridge_connector_create_state() restore max_requested_bpc from connector->max_bpc, so clients that never set the property (fbcon in particular) keep the full range instead of ending up with 0. With the property attached, compositors such as KWin write "max bpc" on every atomic modeset; any in-range value is handled by the existing format filter and bandwidth checks. Signed-off-by: Igor Paunovic <[email protected]> --- drivers/gpu/drm/rockchip/dw_dp-rockchip.c | 26 +++++++++++++++++++++++ 1 file changed, 26 insertions(+) diff --git a/drivers/gpu/drm/rockchip/dw_dp-rockchip.c b/drivers/gpu/drm/rockchip/dw_dp-rockchip.c index 770ab042a187..4dc29963b5d8 100644 --- a/drivers/gpu/drm/rockchip/dw_dp-rockchip.c +++ b/drivers/gpu/drm/rockchip/dw_dp-rockchip.c @@ -172,6 +172,32 @@ static int dw_dp_rockchip_bind(struct device *dev, struct device *master, void * "Failed to init bridge connector\n"); } + /* + * The components are bound before drm_mode_config_reset() runs, so + * the connector has no state yet, but + * drm_connector_attach_max_bpc_property() requires one. Create the + * connector state first, like drmm_connector_hdmi_init() does. + */ + if (connector->funcs->atomic_create_state) { + struct drm_connector_state *state; + + state = connector->funcs->atomic_create_state(connector); + if (IS_ERR(state)) { + dw_dp_unbind(dp->base); + return PTR_ERR(state); + } + + connector->state = state; + } else if (connector->funcs->reset) { + connector->funcs->reset(connector); + } + + ret = drm_connector_attach_max_bpc_property(connector, 6, 10); + if (ret) { + dw_dp_unbind(dp->base); + return ret; + } + return 0; } -- 2.43.0
