USB: option: fix runtime PM handling

commit acf47d4f upstream.

Fix potential I/O while runtime suspended due to missing PM operations
in send_setup.

Fixes: 383cedc3 ("USB: serial: full autosuspend support for the
option driver")
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/usb/serial/option.c

@@ -1955,6 +1955,7 @@ static int option_send_setup(struct usb_serial_port *port)
 	struct usb_wwan_port_private *portdata;
 	int ifNum = serial->interface->cur_altsetting->desc.bInterfaceNumber;
 	int val = 0;
+	int res;
 	dbg("%s", __func__);
 
 	if (is_blacklisted(ifNum, OPTION_BLACKLIST_SENDSETUP,
@@ -1970,9 +1971,16 @@ static int option_send_setup(struct usb_serial_port *port)
 	if (portdata->rts_state)
 		val |= 0x02;
 
-	return usb_control_msg(serial->dev,
-		usb_rcvctrlpipe(serial->dev, 0),
+	res = usb_autopm_get_interface(serial->interface);
+	if (res)
+		return res;
+
+	res = usb_control_msg(serial->dev, usb_rcvctrlpipe(serial->dev, 0),
 		0x22, 0x21, val, ifNum, NULL, 0, USB_CTRL_SET_TIMEOUT);
+
+	usb_autopm_put_interface(serial->interface);
+
+	return res;
 }
 
 MODULE_AUTHOR(DRIVER_AUTHOR);