NFC: Use IDR library to assing NFC devices IDs

As a consequence the NFC device IDs won't be increasing all the time,
as IDR provides the first available ID.
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

include/net/nfc/nfc.h

@@ -95,7 +95,7 @@ struct nfc_genl_data {
 };
 
 struct nfc_dev {
-	unsigned int idx;
+	int idx;
 	u32 target_next_idx;
 	struct nfc_target *targets;
 	int n_targets;

net/nfc/core.c

@@ -40,6 +40,9 @@
 int nfc_devlist_generation;
 DEFINE_MUTEX(nfc_devlist_mutex);
 
+/* NFC device ID bitmap */
+static DEFINE_IDA(nfc_index_ida);
+
 /**
  * nfc_dev_up - turn on the NFC device
  *
@@ -760,7 +763,6 @@ struct nfc_dev *nfc_allocate_device(struct nfc_ops *ops,
 				    u32 supported_protocols,
 				    int tx_headroom, int tx_tailroom)
 {
-	static atomic_t dev_no = ATOMIC_INIT(0);
 	struct nfc_dev *dev;
 
 	if (!ops->start_poll || !ops->stop_poll || !ops->activate_target ||
@@ -774,11 +776,6 @@ struct nfc_dev *nfc_allocate_device(struct nfc_ops *ops,
 	if (!dev)
 		return NULL;
 
-	dev->dev.class = &nfc_class;
-	dev->idx = atomic_inc_return(&dev_no) - 1;
-	dev_set_name(&dev->dev, "nfc%d", dev->idx);
-	device_initialize(&dev->dev);
-
 	dev->ops = ops;
 	dev->supported_protocols = supported_protocols;
 	dev->tx_headroom = tx_headroom;
@@ -814,6 +811,14 @@ int nfc_register_device(struct nfc_dev *dev)
 
 	pr_debug("dev_name=%s\n", dev_name(&dev->dev));
 
+	dev->idx = ida_simple_get(&nfc_index_ida, 0, 0, GFP_KERNEL);
+	if (dev->idx < 0)
+		return dev->idx;
+
+	dev->dev.class = &nfc_class;
+	dev_set_name(&dev->dev, "nfc%d", dev->idx);
+	device_initialize(&dev->dev);
+
 	mutex_lock(&nfc_devlist_mutex);
 	nfc_devlist_generation++;
 	rc = device_add(&dev->dev);
@@ -842,10 +847,12 @@ EXPORT_SYMBOL(nfc_register_device);
  */
 void nfc_unregister_device(struct nfc_dev *dev)
 {
-	int rc;
+	int rc, id;
 
 	pr_debug("dev_name=%s\n", dev_name(&dev->dev));
 
+	id = dev->idx;
+
 	mutex_lock(&nfc_devlist_mutex);
 	nfc_devlist_generation++;
 
@@ -864,6 +871,8 @@ void nfc_unregister_device(struct nfc_dev *dev)
 		pr_debug("The userspace won't be notified that the device %s was removed\n",
 			 dev_name(&dev->dev));
 
+	ida_simple_remove(&nfc_index_ida, id);
+
 }
 EXPORT_SYMBOL(nfc_unregister_device);