drm/connector: Add a fwnode pointer to drm_connector and register with ACPI (v2)

Add a fwnode pointer to struct drm_connector and register an acpi_bus_type
for the connectors with the ACPI subsystem (when CONFIG_ACPI is enabled).

The adding of the fwnode pointer allows drivers to associate a fwnode
that represents a connector with that connector.

When the new fwnode pointer points to an ACPI-companion, then the new
acpi_bus_type will cause the ACPI subsys to bind the device instantiated
for the connector with the fwnode by calling acpi_bind_one(). This will
result in a firmware_node symlink under /sys/class/card#-<connecter-name>/
which helps to verify that the fwnode-s and connectors are properly
matched.

Changes in v2:
- Make drm_connector_cleanup() call fwnode_handle_put() on
  connector->fwnode and document this

Co-developed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Tested-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://lore.kernel.org/r/20210817215201.795062-3-hdegoede@redhat.com

drivers/gpu/drm/drm_connector.c

@@ -474,6 +474,8 @@ void drm_connector_cleanup(struct drm_connector *connector)
 	drm_mode_object_unregister(dev, &connector->base);
 	kfree(connector->name);
 	connector->name = NULL;
+	fwnode_handle_put(connector->fwnode);
+	connector->fwnode = NULL;
 	spin_lock_irq(&dev->mode_config.connector_list_lock);
 	list_del(&connector->head);
 	dev->mode_config.num_connector--;

drivers/gpu/drm/drm_sysfs.c

@@ -10,6 +10,7 @@
  * Copyright (c) 2003-2004 IBM Corp.
  */
 
+#include <linux/acpi.h>
 #include <linux/device.h>
 #include <linux/err.h>
 #include <linux/export.h>
@@ -56,6 +57,39 @@ static struct device_type drm_sysfs_device_connector = {
 
 struct class *drm_class;
 
+#ifdef CONFIG_ACPI
+static bool drm_connector_acpi_bus_match(struct device *dev)
+{
+	return dev->type == &drm_sysfs_device_connector;
+}
+
+static struct acpi_device *drm_connector_acpi_find_companion(struct device *dev)
+{
+	struct drm_connector *connector = to_drm_connector(dev);
+
+	return to_acpi_device_node(connector->fwnode);
+}
+
+static struct acpi_bus_type drm_connector_acpi_bus = {
+	.name = "drm_connector",
+	.match = drm_connector_acpi_bus_match,
+	.find_companion = drm_connector_acpi_find_companion,
+};
+
+static void drm_sysfs_acpi_register(void)
+{
+	register_acpi_bus_type(&drm_connector_acpi_bus);
+}
+
+static void drm_sysfs_acpi_unregister(void)
+{
+	unregister_acpi_bus_type(&drm_connector_acpi_bus);
+}
+#else
+static void drm_sysfs_acpi_register(void) { }
+static void drm_sysfs_acpi_unregister(void) { }
+#endif
+
 static char *drm_devnode(struct device *dev, umode_t *mode)
 {
 	return kasprintf(GFP_KERNEL, "dri/%s", dev_name(dev));
@@ -89,6 +123,8 @@ int drm_sysfs_init(void)
 	}
 
 	drm_class->devnode = drm_devnode;
+
+	drm_sysfs_acpi_register();
 	return 0;
 }
 
@@ -101,6 +137,7 @@ void drm_sysfs_destroy(void)
 {
 	if (IS_ERR_OR_NULL(drm_class))
 		return;
+	drm_sysfs_acpi_unregister();
 	class_remove_file(drm_class, &class_attr_version.attr);
 	class_destroy(drm_class);
 	drm_class = NULL;

include/drm/drm_connector.h

@@ -1228,6 +1228,14 @@ struct drm_connector {
 	struct device *kdev;
 	/** @attr: sysfs attributes */
 	struct device_attribute *attr;
+	/**
+	 * @fwnode: associated fwnode supplied by platform firmware
+	 *
+	 * Drivers can set this to associate a fwnode with a connector, drivers
+	 * are expected to get a reference on the fwnode when setting this.
+	 * drm_connector_cleanup() will call fwnode_handle_put() on this.
+	 */
+	struct fwnode_handle *fwnode;
 
 	/**
 	 * @head: