tty/serial_core: Introduce lock mechanism for RS485

Introduce an homogeneous lock system between setting and using the rs485
data of the uart_port.

This patch should not be split into multiple ones in order to avoid
leaving the tree in an unstable state.

Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Reviewed-by: Alan Cox <alan@linux.intel.com>
Suggested-by: Alan Cox <alan@linux.intel.com>
Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/serial/mcf.c b/drivers/tty/serial/mcf.c
index d7be1f1..fdd5c7b 100644
--- a/drivers/tty/serial/mcf.c
+++ b/drivers/tty/serial/mcf.c
@@ -257,12 +257,12 @@
 		mr2 |= MCFUART_MR2_TXCTS;
 	}
 
+	spin_lock_irqsave(&port->lock, flags);
 	if (port->rs485.flags & SER_RS485_ENABLED) {
 		dev_dbg(port->dev, "Setting UART to RS485\n");
 		mr2 |= MCFUART_MR2_TXRTS;
 	}
 
-	spin_lock_irqsave(&port->lock, flags);
 	uart_update_timeout(port, termios->c_cflag, baud);
 	writeb(MCFUART_UCR_CMDRESETRX, port->membase + MCFUART_UCR);
 	writeb(MCFUART_UCR_CMDRESETTX, port->membase + MCFUART_UCR);
@@ -442,10 +442,8 @@
 static int mcf_config_rs485(struct uart_port *port, struct serial_rs485 *rs485)
 {
 	struct mcf_uart *pp = container_of(port, struct mcf_uart, port);
-	unsigned long flags;
 	unsigned char mr1, mr2;
 
-	spin_lock_irqsave(&port->lock, flags);
 	/* Get mode registers */
 	mr1 = readb(port->membase + MCFUART_UMR);
 	mr2 = readb(port->membase + MCFUART_UMR);
@@ -460,7 +458,6 @@
 	writeb(mr1, port->membase + MCFUART_UMR);
 	writeb(mr2, port->membase + MCFUART_UMR);
 	port->rs485 = *rs485;
-	spin_unlock_irqrestore(&port->lock, flags);
 
 	return 0;
 }