i3c: Handle drivers without probe or remove callback

A registered driver without a probe callback doesn't make sense, so
refuse to register such a driver. (Otherwise i3c_device_probe() yields a
NULL pointer exception.)

A driver without remove is possible, e.g. when all resources are freed
using devm callbacks. So guard the call to driver->remove by a check
for being non-NULL.

Note that the only in-tree i3c driver
(drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_i3c.c) doesn't have a remove
callback.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210128091048.17006-1-u.kleine-koenig@pengutronix.de

drivers/i3c/device.c

@@ -262,6 +262,11 @@ int i3c_driver_register_with_owner(struct i3c_driver *drv, struct module *owner)
 	drv->driver.owner = owner;
 	drv->driver.bus = &i3c_bus_type;
 
+	if (!drv->probe) {
+		pr_err("Trying to register an i3c driver without probe callback\n");
+		return -EINVAL;
+	}
+
 	return driver_register(&drv->driver);
 }
 EXPORT_SYMBOL_GPL(i3c_driver_register_with_owner);

drivers/i3c/master.c

@@ -326,11 +326,13 @@ static int i3c_device_remove(struct device *dev)
 {
 	struct i3c_device *i3cdev = dev_to_i3cdev(dev);
 	struct i3c_driver *driver = drv_to_i3cdrv(dev->driver);
-	int ret;
+	int ret = 0;
 
+	if (driver->remove) {
 		ret = driver->remove(i3cdev);
 		if (ret)
 			return ret;
+	}
 
 	i3c_device_free_ibi(i3cdev);