USB: serial: ch341: fix open and resume after B0

BugLink: http://bugs.launchpad.net/bugs/1658091

commit a20047f3 upstream.

The private baud_rate variable is used to configure the port at open and
reset-resume and must never be set to (and left at) zero or reset-resume
and all further open attempts will fail.

Fixes: aa91def4 ("USB: ch341: set tty baud speed according to tty struct")
Fixes: 664d5df9 ("USB: usb-serial ch341: support for DTR/RTS/CTS")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/usb/serial/ch341.c

@@ -361,12 +361,11 @@ static void ch341_set_termios(struct tty_struct *tty,
 
 	baud_rate = tty_get_baud_rate(tty);
 
-	priv->baud_rate = baud_rate;
-
 	if (baud_rate) {
 		spin_lock_irqsave(&priv->lock, flags);
 		priv->line_control |= (CH341_BIT_DTR | CH341_BIT_RTS);
 		spin_unlock_irqrestore(&priv->lock, flags);
+		priv->baud_rate = baud_rate;
 		ch341_set_baudrate(port->serial->dev, priv);
 	} else {
 		spin_lock_irqsave(&priv->lock, flags);