[PATCH 3/5] drm/rockchip: dw_dp: Attach "max bpc" connector property

[Igor Paunovic]

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 <royalnet026@xxxxxxxxx>
---
 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