Serial: allow port drivers to have a default attribute group

Some serial drivers (like 8250), want to add sysfs files.  We need to do
so in a race-free way, so allow any port to be able to specify an
attribute group that should be added at device creation time.
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial_core.c

@@ -2564,12 +2564,6 @@ static const struct attribute_group tty_dev_attr_group = {
 	.attrs = tty_dev_attrs,
 	};
 
-static const struct attribute_group *tty_dev_attr_groups[] = {
-	&tty_dev_attr_group,
-	NULL
-	};
-
-
 /**
  *	uart_add_one_port - attach a driver-defined port structure
  *	@drv: pointer to the uart low level driver structure for this port
@@ -2586,6 +2580,7 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
 	struct tty_port *port;
 	int ret = 0;
 	struct device *tty_dev;
+	int num_groups;
 
 	BUG_ON(in_interrupt());
 
@@ -2619,12 +2614,26 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
 
 	uart_configure_port(drv, state, uport);
 
+	num_groups = 2;
+	if (uport->attr_group)
+		num_groups++;
+
+	uport->tty_groups = kcalloc(num_groups, sizeof(**uport->tty_groups),
+				    GFP_KERNEL);
+	if (!uport->tty_groups) {
+		ret = -ENOMEM;
+		goto out;
+	}
+	uport->tty_groups[0] = &tty_dev_attr_group;
+	if (uport->attr_group)
+		uport->tty_groups[1] = uport->attr_group;
+
 	/*
 	 * Register the port whether it's detected or not.  This allows
 	 * setserial to be used to alter this port's parameters.
 	 */
 	tty_dev = tty_port_register_device_attr(port, drv->tty_driver,
-			uport->line, uport->dev, port, tty_dev_attr_groups);
+			uport->line, uport->dev, port, uport->tty_groups);
 	if (likely(!IS_ERR(tty_dev))) {
 		device_set_wakeup_capable(tty_dev, 1);
 	} else {
@@ -2703,6 +2712,7 @@ int uart_remove_one_port(struct uart_driver *drv, struct uart_port *uport)
 	 */
 	if (uport->type != PORT_UNKNOWN)
 		uport->ops->release_port(uport);
+	kfree(uport->tty_groups);
 
 	/*
 	 * Indicate that there isn't a port here anymore.

include/linux/serial_core.h

@@ -199,6 +199,8 @@ struct uart_port {
 	unsigned char		suspended;
 	unsigned char		irq_wake;
 	unsigned char		unused[2];
+	struct attribute_group	*attr_group;		/* port specific attributes */
+	const struct attribute_group **tty_groups;	/* all attributes (serial core use only) */
 	void			*private_data;		/* generic platform data pointer */
 };