net: wwan: core: make wwan_class constant

Since commit 43a7206b0963 ("driver core: class: make class_register() take
a const *"), the driver core allows for struct class to be in read-only
memory, so move the wwan_class structure to be declared at build time
placing it into read-only memory, instead of having to be dynamically
allocated at boot time.

Suggested-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Ricardo B. Marliere <[e-mail]>
Acked-by: Sergey Ryazanov <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/wwan/wwan_core.c

···
 static DEFINE_MUTEX(wwan_register_lock); /* WWAN device create|remove lock */
 static DEFINE_IDA(minors); /* minors for WWAN port chardevs */
 static DEFINE_IDA(wwan_dev_ids); /* for unique WWAN device IDs */
-static struct class *wwan_class;
+static const struct class wwan_class = {
+	.name = "wwan",
+};
 static int wwan_major;
 static struct dentry *wwan_debugfs_dir;
 
···
 {
 	struct device *dev;
 
-	dev = class_find_device(wwan_class, NULL, parent, wwan_dev_parent_match);
+	dev = class_find_device(&wwan_class, NULL, parent, wwan_dev_parent_match);
 	if (!dev)
 		return ERR_PTR(-ENODEV);
 
···
 {
 	struct device *dev;
 
-	dev = class_find_device(wwan_class, NULL, name, wwan_dev_name_match);
+	dev = class_find_device(&wwan_class, NULL, name, wwan_dev_name_match);
 	if (!dev)
 		return ERR_PTR(-ENODEV);
 
···
 {
 	struct device *dev;
 
-	dev = class_find_device(wwan_class, NULL, dir, wwan_dev_debugfs_match);
+	dev = class_find_device(&wwan_class, NULL, dir, wwan_dev_debugfs_match);
 	if (!dev)
 		return ERR_PTR(-ENODEV);
 
···
 	}
 
 	wwandev->dev.parent = parent;
-	wwandev->dev.class = wwan_class;
+	wwandev->dev.class = &wwan_class;
 	wwandev->dev.type = &wwan_dev_type;
 	wwandev->id = id;
 	dev_set_name(&wwandev->dev, "wwan%d", wwandev->id);
···
 
 static int is_wwan_child(struct device *dev, void *data)
 {
-	return dev->class == wwan_class;
+	return dev->class == &wwan_class;
 }
 
 static void wwan_remove_dev(struct wwan_device *wwandev)
···
 {
 	struct device *dev;
 
-	dev = class_find_device(wwan_class, NULL, &minor, wwan_port_minor_match);
+	dev = class_find_device(&wwan_class, NULL, &minor, wwan_port_minor_match);
 	if (!dev)
 		return ERR_PTR(-ENODEV);
 
···
 		return -ENOMEM;
 
 	/* Collect ids of same name format ports */
-	class_dev_iter_init(&iter, wwan_class, NULL, &wwan_port_dev_type);
+	class_dev_iter_init(&iter, &wwan_class, NULL, &wwan_port_dev_type);
 	while ((dev = class_dev_iter_next(&iter))) {
 		if (dev->parent != &wwandev->dev)
 			continue;
···
 	mutex_init(&port->data_lock);
 
 	port->dev.parent = &wwandev->dev;
-	port->dev.class = wwan_class;
+	port->dev.class = &wwan_class;
 	port->dev.type = &wwan_port_dev_type;
 	port->dev.devt = MKDEV(wwan_major, minor);
 	dev_set_drvdata(&port->dev, drvdata);
···
 	if (err)
 		return err;
 
-	wwan_class = class_create("wwan");
-	if (IS_ERR(wwan_class)) {
-		err = PTR_ERR(wwan_class);
+	err = class_register(&wwan_class);
+	if (err)
 		goto unregister;
-	}
 
 	/* chrdev used for wwan ports */
 	wwan_major = __register_chrdev(0, 0, WWAN_MAX_MINORS, "wwan_port",
···
 	return 0;
 
 destroy:
-	class_destroy(wwan_class);
+	class_unregister(&wwan_class);
 unregister:
 	rtnl_link_unregister(&wwan_rtnl_link_ops);
 	return err;
···
 	debugfs_remove_recursive(wwan_debugfs_dir);
 	__unregister_chrdev(wwan_major, 0, WWAN_MAX_MINORS, "wwan_port");
 	rtnl_link_unregister(&wwan_rtnl_link_ops);
-	class_destroy(wwan_class);
+	class_unregister(&wwan_class);
 }
 
 module_init(wwan_init);