drm: Add a callback from connector registering

If a driver wants to more precisely control its initialisation and in
particular, defer registering its interfaces with userspace until after
everything is setup, it also needs to defer registering the connectors.
As some devices need more work during registration, add a callback so
that drivers can do additional work if required for a connector.

Correspondingly, we also require an unregister callback.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
[danvet: go ocd and remvoe unecessary empty kerneldoc line.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1465993109-19523-3-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/drm_crtc.c

@@ -990,13 +990,24 @@ int drm_connector_register(struct drm_connector *connector)
 
 	ret = drm_debugfs_connector_add(connector);
 	if (ret) {
-		drm_sysfs_connector_remove(connector);
-		return ret;
+		goto err_sysfs;
+	}
+
+	if (connector->funcs->late_register) {
+		ret = connector->funcs->late_register(connector);
+		if (ret)
+			goto err_debugfs;
 	}
 
 	drm_mode_object_register(connector->dev, &connector->base);
 
 	return 0;
+
+err_debugfs:
+	drm_debugfs_connector_remove(connector);
+err_sysfs:
+	drm_sysfs_connector_remove(connector);
+	return ret;
 }
 EXPORT_SYMBOL(drm_connector_register);
 
@@ -1008,6 +1019,9 @@ EXPORT_SYMBOL(drm_connector_register);
  */
 void drm_connector_unregister(struct drm_connector *connector)
 {
+	if (connector->funcs->early_unregister)
+		connector->funcs->early_unregister(connector);
+
 	drm_sysfs_connector_remove(connector);
 	drm_debugfs_connector_remove(connector);
 }

include/drm/drm_crtc.h

@@ -956,6 +956,33 @@ struct drm_connector_funcs {
 	int (*set_property)(struct drm_connector *connector, struct drm_property *property,
 			     uint64_t val);
 
+	/**
+	 * @late_register:
+	 *
+	 * This optional hook can be used to register additional userspace
+	 * interfaces attached to the connector, light backlight control, i2c,
+	 * DP aux or similar interfaces. It is called late in the driver load
+	 * sequence from drm_connector_register() when registering all the
+	 * core drm connector interfaces. Everything added from this callback
+	 * should be unregistered in the early_unregister callback.
+	 *
+	 * Returns:
+	 *
+	 * 0 on success, or a negative error code on failure.
+	 */
+	int (*late_register)(struct drm_connector *connector);
+
+	/**
+	 * @early_unregister:
+	 *
+	 * This optional hook should be used to unregister the additional
+	 * userspace interfaces attached to the connector from
+	 * late_unregister(). It is called from drm_connector_unregister(),
+	 * early in the driver unload sequence to disable userspace access
+	 * before data structures are torndown.
+	 */
+	void (*early_unregister)(struct drm_connector *connector);
+
 	/**
 	 * @destroy:
 	 *