drm/display/hdmi: implement hotplug functions

The HDMI Connectors need to perform a variety of tasks when the HDMI
connector state changes. Such tasks include setting or invalidating CEC
address, notifying HDMI codec driver, updating scrambler data, etc.

Implementing such tasks in a driver-specific callbacks is error prone.
Start implementing the generic helper function (currently handling only
the HDMI Codec framework) to be used by drivers utilizing HDMI Connector
framework.

Reviewed-by: Maxime Ripard <mripard@kernel.org>
Tested-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241224-drm-bridge-hdmi-connector-v10-6-dc89577cd438@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

drivers/gpu/drm/display/Kconfig

@@ -89,6 +89,7 @@ config DRM_DISPLAY_HDMI_HELPER
 
 config DRM_DISPLAY_HDMI_STATE_HELPER
 	bool
+	select DRM_DISPLAY_HDMI_AUDIO_HELPER
 	select DRM_DISPLAY_HDMI_HELPER
 	help
 	  DRM KMS state helpers for HDMI.

drivers/gpu/drm/display/drm_hdmi_state_helper.c

@@ -5,6 +5,7 @@
 #include <drm/drm_edid.h>
 #include <drm/drm_print.h>
 
+#include <drm/display/drm_hdmi_audio_helper.h>
 #include <drm/display/drm_hdmi_helper.h>
 #include <drm/display/drm_hdmi_state_helper.h>
 
@@ -777,3 +778,59 @@ drm_atomic_helper_connector_hdmi_clear_audio_infoframe(struct drm_connector *con
 	return ret;
 }
 EXPORT_SYMBOL(drm_atomic_helper_connector_hdmi_clear_audio_infoframe);
+
+static void
+drm_atomic_helper_connector_hdmi_update(struct drm_connector *connector,
+					enum drm_connector_status status)
+{
+	const struct drm_edid *drm_edid;
+
+	if (status == connector_status_disconnected) {
+		// TODO: also handle CEC and scramber, HDMI sink disconnected.
+		drm_connector_hdmi_audio_plugged_notify(connector, false);
+	}
+
+	if (connector->hdmi.funcs->read_edid)
+		drm_edid = connector->hdmi.funcs->read_edid(connector);
+	else
+		drm_edid = drm_edid_read(connector);
+
+	drm_edid_connector_update(connector, drm_edid);
+
+	drm_edid_free(drm_edid);
+
+	if (status == connector_status_connected) {
+		// TODO: also handle CEC and scramber, HDMI sink is now connected.
+		drm_connector_hdmi_audio_plugged_notify(connector, true);
+	}
+}
+
+/**
+ * drm_atomic_helper_connector_hdmi_hotplug - Handle the hotplug event for the HDMI connector
+ * @connector: A pointer to the HDMI connector
+ * @status: Connection status
+ *
+ * This function should be called as a part of the .detect() / .detect_ctx()
+ * callbacks, updating the HDMI-specific connector's data.
+ */
+void drm_atomic_helper_connector_hdmi_hotplug(struct drm_connector *connector,
+					      enum drm_connector_status status)
+{
+	drm_atomic_helper_connector_hdmi_update(connector, status);
+}
+EXPORT_SYMBOL(drm_atomic_helper_connector_hdmi_hotplug);
+
+/**
+ * drm_atomic_helper_connector_hdmi_force - HDMI Connector implementation of the force callback
+ * @connector: A pointer to the HDMI connector
+ *
+ * This function implements the .force() callback for the HDMI connectors. It
+ * can either be used directly as the callback or should be called from within
+ * the .force() callback implementation to maintain the HDMI-specific
+ * connector's data.
+ */
+void drm_atomic_helper_connector_hdmi_force(struct drm_connector *connector)
+{
+	drm_atomic_helper_connector_hdmi_update(connector, connector->status);
+}
+EXPORT_SYMBOL(drm_atomic_helper_connector_hdmi_force);

include/drm/display/drm_hdmi_state_helper.h

@@ -8,6 +8,8 @@ struct drm_connector;
 struct drm_connector_state;
 struct hdmi_audio_infoframe;
 
+enum drm_connector_status;
+
 void __drm_atomic_helper_connector_hdmi_reset(struct drm_connector *connector,
 					      struct drm_connector_state *new_conn_state);
 
@@ -19,6 +21,9 @@ int drm_atomic_helper_connector_hdmi_update_audio_infoframe(struct drm_connector
 int drm_atomic_helper_connector_hdmi_clear_audio_infoframe(struct drm_connector *connector);
 int drm_atomic_helper_connector_hdmi_update_infoframes(struct drm_connector *connector,
 						       struct drm_atomic_state *state);
+void drm_atomic_helper_connector_hdmi_hotplug(struct drm_connector *connector,
+					      enum drm_connector_status status);
+void drm_atomic_helper_connector_hdmi_force(struct drm_connector *connector);
 
 enum drm_mode_status
 drm_hdmi_connector_mode_valid(struct drm_connector *connector,

include/drm/drm_connector.h

@@ -45,6 +45,7 @@ struct drm_property;
 struct drm_property_blob;
 struct drm_printer;
 struct drm_privacy_screen;
+struct drm_edid;
 struct edid;
 struct hdmi_codec_daifmt;
 struct hdmi_codec_params;
@@ -1247,6 +1248,21 @@ struct drm_connector_hdmi_funcs {
 	int (*write_infoframe)(struct drm_connector *connector,
 			       enum hdmi_infoframe_type type,
 			       const u8 *buffer, size_t len);
+
+	/**
+	 * @read_edid:
+	 *
+	 * This callback is used by the framework as a replacement for reading
+	 * the EDID from connector->ddc. It is still recommended to provide
+	 * connector->ddc instead of implementing this callback. Returned EDID
+	 * should be freed via the drm_edid_free().
+	 *
+	 * The @read_edid callback is optional.
+	 *
+	 * Returns:
+	 * Valid EDID on success, NULL in case of failure.
+	 */
+	const struct drm_edid *(*read_edid)(struct drm_connector *connector);
 };
 
 /**