[PATCH] serial: make sure UART is powered up when dumping MCTRL status

Since serial devices are powered down when not in use and some of those
devices cannot be accessed when powered down, we need to enable power
around calls to get_mcrtl() when dumping port state via uart_line_info().
This resolves hangs observed on some machines while reading serial device
registers when a port is powered off.

Signed-off-by: George G. Davis <gdavis@mvista.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/serial/serial_core.c

@@ -1660,6 +1660,7 @@ static const char *uart_type(struct uart_port *port)
 static int uart_line_info(char *buf, struct uart_driver *drv, int i)
 {
 	struct uart_state *state = drv->state + i;
+	int pm_state;
 	struct uart_port *port = state->port;
 	char stat_buf[32];
 	unsigned int status;
@@ -1682,9 +1683,16 @@ static int uart_line_info(char *buf, struct uart_driver *drv, int i)
 
 	if(capable(CAP_SYS_ADMIN))
 	{
+		mutex_lock(&state->mutex);
+		pm_state = state->pm_state;
+		if (pm_state)
+			uart_change_pm(state, 0);
 		spin_lock_irq(&port->lock);
 		status = port->ops->get_mctrl(port);
 		spin_unlock_irq(&port->lock);
+		if (pm_state)
+			uart_change_pm(state, pm_state);
+		mutex_unlock(&state->mutex);
 
 		ret += sprintf(buf + ret, " tx:%d rx:%d",
 				port->icount.tx, port->icount.rx);
@@ -2100,6 +2108,9 @@ uart_configure_port(struct uart_driver *drv, struct uart_state *state,
 
 		uart_report_port(drv, port);
 
+		/* Power up port for set_mctrl() */
+		uart_change_pm(state, 0);
+
 		/*
 		 * Ensure that the modem control lines are de-activated.
 		 * We probably don't need a spinlock around this, but