[PATCH] Make sure UART is powered up when dumping MCTRL status

[PATCH] Make sure UART is powered up when dumping MCTRL status

[George G. Davis]

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>

 drivers/serial/serial_core.c |   11 +++++++++++
 1 files changed, 11 insertions(+)


Index: linux-2.6/drivers/serial/serial_core.c
===================================================================
--- linux-2.6.orig/drivers/serial/serial_core.c
+++ linux-2.6/drivers/serial/serial_core.c
@@ -1652,6 +1652,7 @@ static const char *uart_type(struct uart
 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;
@@ -1674,9 +1675,16 @@ static int uart_line_info(char *buf, str
 
 	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);
@@ -2071,6 +2079,9 @@ uart_configure_port(struct uart_driver *
 
 		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


FYI: I've posted the above to the linux-serial mailing list but have not
received any additional feedback after reworking to incorporate changes
recommended via that mailing list.  That thread ends here:

http://www.spinics.net/lists/linux-serial/msg00196.html

I'm now posting this reworked version to linux-kernel to move this along.

TIA for comments/feedback!

--
Regards,
George