drm/radeon: add late_register for connector

The patch is to solve null dereference in 'aux.dev', which is
introduced in recent radeon rework. By having 'late_register',
the connector should be registered after 'drm_dev_register'
automatically, where in before it is the opposite.

Fixes: 90985660ba48 ("drm/radeon: remove load callback from kms_driver")
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3665
Tested-by: Hans de Goede <[e-mail]>
Suggested-by: Christophe Leroy <[e-mail]>
Signed-off-by: Wu Hoi Pok <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/radeon/atombios_dp.c

···
 {
 	struct drm_device *dev = radeon_connector->base.dev;
 	struct radeon_device *rdev = dev->dev_private;
-	int ret;
 
 	radeon_connector->ddc_bus->rec.hpd = radeon_connector->hpd.hpd;
-	radeon_connector->ddc_bus->aux.dev = radeon_connector->base.kdev;
 	radeon_connector->ddc_bus->aux.drm_dev = radeon_connector->base.dev;
 	if (ASIC_IS_DCE5(rdev)) {
 		if (radeon_auxch)
···
 		radeon_connector->ddc_bus->aux.transfer = radeon_dp_aux_transfer_atom;
 	}
 
-	ret = drm_dp_aux_register(&radeon_connector->ddc_bus->aux);
-	if (!ret)
-		radeon_connector->ddc_bus->has_aux = true;
-
-	WARN(ret, "drm_dp_aux_register() failed with error %d\n", ret);
+	drm_dp_aux_init(&radeon_connector->ddc_bus->aux);
+	radeon_connector->ddc_bus->has_aux = true;
 }
 
 /***** general DP utility functions *****/

drivers/gpu/drm/radeon/radeon_connectors.c

···
 	return MODE_OK;
 }
 
+static int
+radeon_connector_late_register(struct drm_connector *connector)
+{
+	struct radeon_connector *radeon_connector = to_radeon_connector(connector);
+	int r = 0;
+
+	if (radeon_connector->ddc_bus->has_aux) {
+		radeon_connector->ddc_bus->aux.dev = radeon_connector->base.kdev;
+		r = drm_dp_aux_register(&radeon_connector->ddc_bus->aux);
+	}
+
+	return r;
+}
+
 static const struct drm_connector_helper_funcs radeon_dp_connector_helper_funcs = {
 	.get_modes = radeon_dp_get_modes,
 	.mode_valid = radeon_dp_mode_valid,
···
 	.early_unregister = radeon_connector_unregister,
 	.destroy = radeon_connector_destroy,
 	.force = radeon_dvi_force,
+	.late_register = radeon_connector_late_register,
 };
 
 static const struct drm_connector_funcs radeon_edp_connector_funcs = {
···
 	.early_unregister = radeon_connector_unregister,
 	.destroy = radeon_connector_destroy,
 	.force = radeon_dvi_force,
+	.late_register = radeon_connector_late_register,
 };
 
 static const struct drm_connector_funcs radeon_lvds_bridge_connector_funcs = {
···
 	.early_unregister = radeon_connector_unregister,
 	.destroy = radeon_connector_destroy,
 	.force = radeon_dvi_force,
+	.late_register = radeon_connector_late_register,
 };
 
 void