USB: serial: ch341: fix resume after reset

commit ce5e2928 upstream.

Fix reset-resume handling which failed to resubmit the read and
interrupt URBs, thereby leaving a port that was open before suspend in a
broken state until closed and reopened.

Fixes: 1ded7ea4 ("USB: ch341 serial: fix port number changed after
resume")
Fixes: 2bfd1c96 ("USB: serial: ch341: remove reset_resume callback")
Signed-off-by: Johan Hovold <johan@kernel.org>
[bwh: Backported to 3.16: open-code tty_port_initialized()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/usb/serial/ch341.c

@@ -559,14 +559,23 @@ static int ch341_tiocmget(struct tty_struct *tty)
 
 static int ch341_reset_resume(struct usb_serial *serial)
 {
-	struct ch341_private *priv;
-
-	priv = usb_get_serial_port_data(serial->port[0]);
+	struct usb_serial_port *port = serial->port[0];
+	struct ch341_private *priv = usb_get_serial_port_data(port);
+	int ret;
 
 	/* reconfigure ch341 serial port after bus-reset */
 	ch341_configure(serial->dev, priv);
 
-	return 0;
+	if (port->port.flags & ASYNC_INITIALIZED) {
+		ret = usb_submit_urb(port->interrupt_in_urb, GFP_NOIO);
+		if (ret) {
+			dev_err(&port->dev, "failed to submit interrupt urb: %d\n",
+				ret);
+			return ret;
+		}
+	}
+
+	return usb_serial_generic_resume(serial);
 }
 
 static struct usb_serial_driver ch341_device = {