greybus: uart: Kill reference_count hack

This was done long back and was probably the best bet then, but it looks
really bad to have it this way now.

Kill the hack and implement proper driver init()/exit() routines to do
the same thing.

Tested using gbsim by hotplugging uart manifest and removing it later.
Also tried removing the gb-phy module to test the exit path properly.
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Vaibhav Hiremath <vaibhav.hiremath@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/uart.c

@@ -65,7 +65,6 @@ struct gb_tty {
 static struct tty_driver *gb_tty_driver;
 static DEFINE_IDR(tty_minors);
 static DEFINE_MUTEX(table_lock);
-static atomic_t reference_count = ATOMIC_INIT(0);
 
 static int gb_uart_receive_data_handler(struct gb_operation *op)
 {
@@ -553,6 +552,7 @@ static int wait_serial_change(struct gb_tty *gb_tty, unsigned long arg)
 	} while (!retval);
 
 	return retval;
+
 }
 
 static int get_serial_usage(struct gb_tty *gb_tty,
@@ -619,9 +619,6 @@ static const struct tty_operations gb_ops = {
 
 static struct tty_port_operations null_ops = { };
 
-static int gb_tty_init(void);
-static void gb_tty_exit(void);
-
 static int gb_uart_probe(struct gpbridge_device *gpbdev,
 			 const struct gpbridge_device_id *id)
 {
@@ -632,20 +629,9 @@ static int gb_uart_probe(struct gpbridge_device *gpbdev,
 	int retval;
 	int minor;
 
-	/* First time here, initialize the tty structures */
-	if (atomic_inc_return(&reference_count) == 1) {
-		retval = gb_tty_init();
-		if (retval) {
-			atomic_dec(&reference_count);
-			return retval;
-		}
-	}
-
 	gb_tty = kzalloc(sizeof(*gb_tty), GFP_KERNEL);
-	if (!gb_tty) {
-		retval = -ENOMEM;
-		goto exit_tty;
-	}
+	if (!gb_tty)
+		return -ENOMEM;
 
 	connection = gb_connection_create(gpbdev->bundle,
 					  le16_to_cpu(gpbdev->cport_desc->id),
@@ -737,9 +723,6 @@ static int gb_uart_probe(struct gpbridge_device *gpbdev,
 	gb_connection_destroy(connection);
 exit_tty_free:
 	kfree(gb_tty);
-exit_tty:
-	if (atomic_dec_return(&reference_count) == 0)
-		gb_tty_exit();
 
 	return retval;
 }
@@ -772,10 +755,6 @@ static void gb_uart_remove(struct gpbridge_device *gpbdev)
 	gb_connection_destroy(connection);
 	kfree(gb_tty->buffer);
 	kfree(gb_tty);
-
-	/* If last device is gone, tear down the tty structures */
-	if (atomic_dec_return(&reference_count) == 0)
-		gb_tty_exit();
 }
 
 static int gb_tty_init(void)
@@ -832,4 +811,26 @@ static struct gpbridge_driver uart_driver = {
 	.remove		= gb_uart_remove,
 	.id_table	= gb_uart_id_table,
 };
-gb_gpbridge_builtin_driver(uart_driver);
+
+int gb_uart_driver_init(void)
+{
+	int ret;
+
+	ret = gb_tty_init();
+	if (ret)
+		return ret;
+
+	ret = gb_gpbridge_register(&uart_driver);
+	if (ret) {
+		gb_tty_exit();
+		return ret;
+	}
+
+	return 0;
+}
+
+void gb_uart_driver_exit(void)
+{
+	gb_gpbridge_deregister(&uart_driver);
+	gb_tty_exit();
+}