USB: serial: f81232: implement break control

Implement Fintek F81232 break on/off with LCR register.
It's the same with 16550A LCR register layout.
Signed-off-by: Ji-Ze Hong (Peter Hong) <hpeter+linux_kernel@gmail.com>
[ johan: fix corrupt line settings on break due to missing shadow_lcr
  update in set_termios() ]
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/f81232.c

@@ -65,6 +65,7 @@ struct f81232_private {
 	struct mutex lock;
 	u8 modem_control;
 	u8 modem_status;
+	u8 shadow_lcr;
 	speed_t baud_base;
 	struct work_struct lsr_work;
 	struct work_struct interrupt_work;
@@ -377,13 +378,23 @@ static void f81232_process_read_urb(struct urb *urb)
 
 static void f81232_break_ctl(struct tty_struct *tty, int break_state)
 {
-	/* FIXME - Stubbed out for now */
+	struct usb_serial_port *port = tty->driver_data;
+	struct f81232_private *priv = usb_get_serial_port_data(port);
+	int status;
 
-	/*
-	 * break_state = -1 to turn on break, and 0 to turn off break
-	 * see drivers/char/tty_io.c to see it used.
-	 * last_set_data_urb_value NEVER has the break bit set in it.
-	 */
+	mutex_lock(&priv->lock);
+
+	if (break_state)
+		priv->shadow_lcr |= UART_LCR_SBC;
+	else
+		priv->shadow_lcr &= ~UART_LCR_SBC;
+
+	status = f81232_set_register(port, LINE_CONTROL_REGISTER,
+					priv->shadow_lcr);
+	if (status)
+		dev_err(&port->dev, "set break failed: %d\n", status);
+
+	mutex_unlock(&priv->lock);
 }
 
 static int f81232_find_clk(speed_t baudrate)
@@ -519,6 +530,7 @@ static int f81232_port_disable(struct usb_serial_port *port)
 static void f81232_set_termios(struct tty_struct *tty,
 		struct usb_serial_port *port, struct ktermios *old_termios)
 {
+	struct f81232_private *priv = usb_get_serial_port_data(port);
 	u8 new_lcr = 0;
 	int status = 0;
 	speed_t baudrate;
@@ -572,11 +584,18 @@ static void f81232_set_termios(struct tty_struct *tty,
 		break;
 	}
 
+	mutex_lock(&priv->lock);
+
+	new_lcr |= (priv->shadow_lcr & UART_LCR_SBC);
 	status = f81232_set_register(port, LINE_CONTROL_REGISTER, new_lcr);
 	if (status) {
 		dev_err(&port->dev, "%s failed to set LCR: %d\n",
 			__func__, status);
 	}
+
+	priv->shadow_lcr = new_lcr;
+
+	mutex_unlock(&priv->lock);
 }
 
 static int f81232_tiocmget(struct tty_struct *tty)