[SERIAL] Locking fixup (part 2)

After the last few days of debugging, we've ended up with the caller
of the start_tx and stop_tx methods taking the per-port lock.  This
cset and the accompanying csets make the same change to some of the
other methods for consistency reasons.  Since these methods don't
contain a lot of code, it is better that they have consistent locking
rules.

This cset fixes up the enable_ms method.

Documentation/serial/driver

@@ -145,8 +145,9 @@ hardware.
   enable_ms(port)
 	Enable the modem status interrupts.
 
-	Locking: none.
-	Interrupts: caller dependent.
+	Locking: port->lock taken.
+	Interrupts: locally disabled.
+	This call must not sleep
 
   break_ctl(port,ctl)
 	Control the transmission of a break signal.  If ctl is

drivers/serial/8250.c

@@ -733,12 +733,9 @@ static void serial8250_stop_rx(struct uart_port *port)
 static void serial8250_enable_ms(struct uart_port *port)
 {
 	struct uart_8250_port *up = (struct uart_8250_port *)port;
-	unsigned long flags;
 
-	spin_lock_irqsave(&up->port.lock, flags);
 	up->ier |= UART_IER_MSI;
 	serial_out(up, UART_IER, up->ier);
-	spin_unlock_irqrestore(&up->port.lock, flags);
 }
 
 static _INLINE_ void
@@ -1360,6 +1357,12 @@ serial8250_change_speed(struct uart_port *port, unsigned int cflag,
 	if ((cflag & CREAD) == 0)
 		up->port.ignore_status_mask |= UART_LSR_DR;
 
+	/*
+	 * Ok, we're now changing the port state.  Do it with
+	 * interrupts disabled.
+	 */
+	spin_lock_irqsave(&up->port.lock, flags);
+
 	/*
 	 * CTS flow control flag and modem status interrupts
 	 */
@@ -1367,11 +1370,6 @@ serial8250_change_speed(struct uart_port *port, unsigned int cflag,
 	if (UART_ENABLE_MS(&up->port, cflag))
 		up->ier |= UART_IER_MSI;
 
-	/*
-	 * Ok, we're now changing the port state.  Do it with
-	 * interrupts disabled.
-	 */
-	spin_lock_irqsave(&up->port.lock, flags);
 	serial_out(up, UART_IER, up->ier);
 
 	if (uart_config[up->port.type].flags & UART_STARTECH) {

drivers/serial/amba.c

@@ -147,14 +147,11 @@ static void ambauart_stop_rx(struct uart_port *port)
 
 static void ambauart_enable_ms(struct uart_port *port)
 {
-	unsigned long flags;
 	unsigned int cr;
 
-	spin_lock_irqsave(&port->lock, flags);
 	cr = UART_GET_CR(port);
 	cr |= AMBA_UARTCR_MSIE;
 	UART_PUT_CR(port, cr);
-	spin_unlock_irqrestore(&port->lock, flags);
 }
 
 static void

drivers/serial/core.c

@@ -931,12 +931,12 @@ uart_wait_modem_status(struct uart_info *info, unsigned long arg)
 	 */
 	spin_lock_irq(&port->lock);
 	memcpy(&cprev, &port->icount, sizeof(struct uart_icount));
-	spin_unlock_irq(&port->lock);
 
 	/*
 	 * Force modem status interrupts on
 	 */
 	port->ops->enable_ms(port);
+	spin_unlock_irq(&port->lock);
 
 	add_wait_queue(&info->delta_msr_wait, &wait);
 	for (;;) {

drivers/serial/sa1100.c

@@ -423,7 +423,9 @@ static int sa1100_startup(struct uart_port *port)
 	/*
 	 * Enable modem status interrupts
 	 */
+	spin_lock_irq(&sport->port.lock);
 	sa1100_enable_ms(&sport->port);
+	spin_unlock_irq(&sport->port.lock);
 
 	return 0;
 }
@@ -524,10 +526,11 @@ sa1100_change_speed(struct uart_port *port, unsigned int cflag,
 	UART_PUT_UTSR0(sport, -1);
 
 	UART_PUT_UTCR3(sport, old_utcr3);
-	spin_unlock_irqrestore(&sport->port.lock, flags);
 
 	if (UART_ENABLE_MS(&sport->port, cflag))
 		sa1100_enable_ms(&sport->port);
+
+	spin_unlock_irqrestore(&sport->port.lock, flags);
 }
 
 static const char *sa1100_type(struct uart_port *port)