drm/bridge: lt8912b: Add hot plug detection

Enable hot plug detection when it is available on the HDMI port.
Without this connecting to a different monitor with incompatible timing
before the 10 seconds poll period will lead to a broken display output.

Fixes: 30e2ae94 ("drm/bridge: Introduce LT8912B DSI to HDMI bridge")
Signed-off-by: Stefan Eichenberger <stefan.eichenberger@toradex.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Reviewed-by: Adrien Grassein <adrien.grassein@gmail.com>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20221128112320.25708-1-francesco@dolcini.it

drivers/gpu/drm/bridge/lontium-lt8912b.c

@@ -517,14 +517,27 @@ static int lt8912_attach_dsi(struct lt8912 *lt)
 	return 0;
 }
 
+static void lt8912_bridge_hpd_cb(void *data, enum drm_connector_status status)
+{
+	struct lt8912 *lt = data;
+
+	if (lt->bridge.dev)
+		drm_helper_hpd_irq_event(lt->bridge.dev);
+}
+
 static int lt8912_bridge_connector_init(struct drm_bridge *bridge)
 {
 	int ret;
 	struct lt8912 *lt = bridge_to_lt8912(bridge);
 	struct drm_connector *connector = &lt->connector;
 
-	connector->polled = DRM_CONNECTOR_POLL_CONNECT |
-			    DRM_CONNECTOR_POLL_DISCONNECT;
+	if (lt->hdmi_port->ops & DRM_BRIDGE_OP_HPD) {
+		drm_bridge_hpd_enable(lt->hdmi_port, lt8912_bridge_hpd_cb, lt);
+		connector->polled = DRM_CONNECTOR_POLL_HPD;
+	} else {
+		connector->polled = DRM_CONNECTOR_POLL_CONNECT |
+				    DRM_CONNECTOR_POLL_DISCONNECT;
+	}
 
 	ret = drm_connector_init(bridge->dev, connector,
 				 &lt8912_connector_funcs,
@@ -578,6 +591,10 @@ static void lt8912_bridge_detach(struct drm_bridge *bridge)
 
 	if (lt->is_attached) {
 		lt8912_hard_power_off(lt);
+
+		if (lt->hdmi_port->ops & DRM_BRIDGE_OP_HPD)
+			drm_bridge_hpd_disable(lt->hdmi_port);
+
 		drm_connector_unregister(&lt->connector);
 		drm_connector_cleanup(&lt->connector);
 	}