extcon: Use unique number for the extcon device ID

The use of atomic variable is still racy when we do not control which
device has been unregistered and there is a (theoretical) possibility
of the overflow that may cause a duplicate extcon device ID number
to be allocated next time a device is registered.

Replace above mentioned approach by using IDA framework.

Signed-off-by: Andy Shevchenko <[e-mail]>
Signed-off-by: Chanwoo Choi <[e-mail]>

drivers/extcon/extcon.c

···
 
 #include <linux/module.h>
 #include <linux/types.h>
+#include <linux/idr.h>
 #include <linux/init.h>
 #include <linux/device.h>
 #include <linux/fs.h>
···
 
 static struct class *extcon_class;
 
+static DEFINE_IDA(extcon_dev_ids);
 static LIST_HEAD(extcon_dev_list);
 static DEFINE_MUTEX(extcon_dev_list_lock);
 
···
 int extcon_dev_register(struct extcon_dev *edev)
 {
 	int ret, index = 0;
-	static atomic_t edev_no = ATOMIC_INIT(-1);
 
 	ret = create_extcon_class();
 	if (ret < 0)
···
 			"extcon device name is null\n");
 		return -EINVAL;
 	}
-	dev_set_name(&edev->dev, "extcon%lu",
-			(unsigned long)atomic_inc_return(&edev_no));
+
+	ret = ida_alloc(&extcon_dev_ids, GFP_KERNEL);
+	if (ret < 0)
+		return ret;
+
+	edev->id = ret;
+
+	dev_set_name(&edev->dev, "extcon%d", edev->id);
 
 	ret = extcon_alloc_cables(edev);
 	if (ret < 0)
···
 	if (edev->max_supported)
 		kfree(edev->cables);
 err_alloc_cables:
+	ida_free(&extcon_dev_ids, edev->id);
 
 	return ret;
 }
···
 		dev_err(&edev->dev, "Failed to unregister extcon_dev\n");
 		return;
 	}
+
+	ida_free(&extcon_dev_ids, edev->id);
 
 	device_unregister(&edev->dev);
 

drivers/extcon/extcon.h

···
  *			{0x3, 0x6, 0x5, 0}. If it is {0xFFFFFFFF, 0}, there
  *			can be no simultaneous connections.
  * @dev:		Device of this extcon.
+ * @id:			Unique device ID of this extcon.
  * @state:		Attach/detach state of this extcon. Do not provide at
  *			register-time.
  * @nh_all:		Notifier for the state change events for all supported
···
 
 	/* Internal data. Please do not set. */
 	struct device dev;
+	unsigned int id;
 	struct raw_notifier_head nh_all;
 	struct raw_notifier_head *nh;
 	struct list_head entry;