usb: mtu3: Convert to platform remove callback returning void

The .remove() callback for a platform driver returns an int which makes
many driver authors wrongly assume it's possible to do error handling by
returning an error code. However the value returned is (mostly) ignored
and this typically results in resource leaks. To improve here there is a
quest to make the remove callback return void. In the first step of this
quest all drivers are converted to .remove_new() which already returns
void.

The function mtu3_remove() can only return a non-zero value if
ssusb->dr_mode is neiter USB_DR_MODE_PERIPHERAL nor USB_DR_MODE_HOST nor
USB_DR_MODE_OTG. In this case however the probe callback doesn't succeed
and so the remove callback isn't called at all. So the code branch
resulting in this error path could just be dropped were it not for the
compiler choking on "enumeration value 'USB_DR_MODE_UNKNOWN' not handled
in switch [-Werror=switch]". So instead replace this code path by a
WARN_ON and then mtu3_remove() be converted to return void trivially.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20231020151537.2202675-2-u.kleine-koenig@pengutronix.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/mtu3/mtu3_plat.c

@@ -451,7 +451,7 @@ static int mtu3_probe(struct platform_device *pdev)
 	return ret;
 }
 
-static int mtu3_remove(struct platform_device *pdev)
+static void mtu3_remove(struct platform_device *pdev)
 {
 	struct ssusb_mtk *ssusb = platform_get_drvdata(pdev);
 
@@ -469,8 +469,16 @@ static int mtu3_remove(struct platform_device *pdev)
 		ssusb_gadget_exit(ssusb);
 		ssusb_host_exit(ssusb);
 		break;
-	default:
-		return -EINVAL;
+	case USB_DR_MODE_UNKNOWN:
+		/*
+		 * This cannot happen because with dr_mode ==
+		 * USB_DR_MODE_UNKNOWN, .probe() doesn't succeed and so
+		 * .remove() wouldn't be called at all. However (little
+		 * surprising) the compiler isn't smart enough to see that, so
+		 * we explicitly have this case item to not make the compiler
+		 * wail about an unhandled enumeration value.
+		 */
+		break;
 	}
 
 	ssusb_rscs_exit(ssusb);
@@ -478,8 +486,6 @@ static int mtu3_remove(struct platform_device *pdev)
 	pm_runtime_disable(&pdev->dev);
 	pm_runtime_put_noidle(&pdev->dev);
 	pm_runtime_set_suspended(&pdev->dev);
-
-	return 0;
 }
 
 static int resume_ip_and_ports(struct ssusb_mtk *ssusb, pm_message_t msg)
@@ -615,7 +621,7 @@ MODULE_DEVICE_TABLE(of, mtu3_of_match);
 
 static struct platform_driver mtu3_driver = {
 	.probe = mtu3_probe,
-	.remove = mtu3_remove,
+	.remove_new = mtu3_remove,
 	.driver = {
 		.name = MTU3_DRIVER_NAME,
 		.pm = DEV_PM_OPS,