device-dax: utilize new cdev_device_add helper function

Replace the open coded registration of the cdev and dev with the
new device_add_cdev() helper. The helper replaces a common pattern by
taking the proper reference against the parent device and adding both
the cdev and the device.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/dax/dax.c

@@ -677,8 +677,6 @@ static void dax_dev_release(struct device *dev)
 
 static void kill_dax_dev(struct dax_dev *dax_dev)
 {
-	struct cdev *cdev = &dax_dev->cdev;
-
 	/*
 	 * Note, rcu is not protecting the liveness of dax_dev, rcu is
 	 * ensuring that any fault handlers that might have seen
@@ -689,7 +687,6 @@ static void kill_dax_dev(struct dax_dev *dax_dev)
 	dax_dev->alive = false;
 	synchronize_rcu();
 	unmap_mapping_range(dax_dev->inode->i_mapping, 0, 0, 1);
-	cdev_del(cdev);
 }
 
 static void unregister_dax_dev(void *dev)
@@ -699,7 +696,8 @@ static void unregister_dax_dev(void *dev)
 	dev_dbg(dev, "%s\n", __func__);
 
 	kill_dax_dev(dax_dev);
-	device_unregister(dev);
+	cdev_device_del(&dax_dev->cdev, dev);
+	put_device(dev);
 }
 
 struct dax_dev *devm_create_dax_dev(struct dax_region *dax_region,
@@ -750,18 +748,13 @@ struct dax_dev *devm_create_dax_dev(struct dax_region *dax_region,
 		goto err_inode;
 	}
 
-	/* device_initialize() so cdev can reference kobj parent */
+	/* from here on we're committed to teardown via dax_dev_release() */
 	device_initialize(dev);
 
 	cdev = &dax_dev->cdev;
 	cdev_init(cdev, &dax_fops);
 	cdev->owner = parent->driver->owner;
-	cdev->kobj.parent = &dev->kobj;
-	rc = cdev_add(&dax_dev->cdev, dev_t, 1);
-	if (rc)
-		goto err_cdev;
 
-	/* from here on we're committed to teardown via dax_dev_release() */
 	dax_dev->num_resources = count;
 	dax_dev->alive = true;
 	dax_dev->region = dax_region;
@@ -773,7 +766,8 @@ struct dax_dev *devm_create_dax_dev(struct dax_region *dax_region,
 	dev->groups = dax_attribute_groups;
 	dev->release = dax_dev_release;
 	dev_set_name(dev, "dax%d.%d", dax_region->id, dax_dev->id);
-	rc = device_add(dev);
+
+	rc = cdev_device_add(cdev, dev);
 	if (rc) {
 		kill_dax_dev(dax_dev);
 		put_device(dev);
@@ -786,8 +780,6 @@ struct dax_dev *devm_create_dax_dev(struct dax_region *dax_region,
 
 	return dax_dev;
 
- err_cdev:
-	iput(dax_dev->inode);
  err_inode:
 	ida_simple_remove(&dax_minor_ida, minor);
  err_minor: