drm: zynqmp_kms: Fix AUX bus not getting unregistered

drm_encoder_cleanup is responsible for calling drm_bridge_detach for
each bridge attached to the encoder. zynqmp_dp_bridge_detach is in turn
responsible for unregistering the AUX bus. However, we never ended up
calling drm_encoder_cleanup in the remove or error paths, so the AUX bus
would stick around after the rest of the driver had been removed.

I don't really understand why drm_mode_config_cleanup doesn't call
drm_encoder_cleanup for us. It will call destroy (which for
simple_encoder is drm_encoder_cleanup) on encoders in the mode_config's
encoder_list.

Should drm_encoder_cleanup get called before or after
drm_atomic_helper_shutdown?

Fixes: 2dfd045c ("drm: xlnx: zynqmp_dpsub: Register AUX bus at bridge attach time")
Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240503192922.2172314-2-sean.anderson@linux.dev

drivers/gpu/drm/xlnx/zynqmp_kms.c

@@ -437,23 +437,28 @@ static int zynqmp_dpsub_kms_init(struct zynqmp_dpsub *dpsub)
 				DRM_BRIDGE_ATTACH_NO_CONNECTOR);
 	if (ret) {
 		dev_err(dpsub->dev, "failed to attach bridge to encoder\n");
-		return ret;
+		goto err_encoder;
 	}
 
 	/* Create the connector for the chain of bridges. */
 	connector = drm_bridge_connector_init(&dpsub->drm->dev, encoder);
 	if (IS_ERR(connector)) {
 		dev_err(dpsub->dev, "failed to created connector\n");
-		return PTR_ERR(connector);
+		ret = PTR_ERR(connector);
+		goto err_encoder;
 	}
 
 	ret = drm_connector_attach_encoder(connector, encoder);
 	if (ret < 0) {
 		dev_err(dpsub->dev, "failed to attach connector to encoder\n");
-		return ret;
+		goto err_encoder;
 	}
 
 	return 0;
+
+err_encoder:
+	drm_encoder_cleanup(encoder);
+	return ret;
 }
 
 static void zynqmp_dpsub_drm_release(struct drm_device *drm, void *res)
@@ -533,5 +538,6 @@ void zynqmp_dpsub_drm_cleanup(struct zynqmp_dpsub *dpsub)
 
 	drm_dev_unregister(drm);
 	drm_atomic_helper_shutdown(drm);
+	drm_encoder_cleanup(&dpsub->drm->encoder);
 	drm_kms_helper_poll_fini(drm);
 }