serial_core: fix uart PORT_UNKNOWN handling

While porting a RS485 driver from 2.6.29 to 3.14, i noticed that the serial tty
driver could break it by using uart ports that it does not own :

1. uart_change_pm ist called during uart_open and calls the uart pm function
   without checking for PORT_UNKNOWN.
   The fix is to move uart_change_pm from uart_open to uart_port_startup.
2. The return code from the uart request_port call in uart_set_info is not
   handled properly, leading to the situation that the serial driver also
   thinks it owns the uart ports.
   This can triggered by doing following actions :

   setserial /dev/ttyS0 uart none    # release the uart ports
   modprobe lirc-serial              # or any other device that uses the uart
   setserial /dev/ttyS0 uart 16550   # gives no error and the uart tty driver
                                     # can use the ports as well

Signed-off-by: Thomas Pfaff <tpfaff@pcs.com>
Reviewed-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 21 insertions, 18 deletions

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index f26834d262b3..b68550d95a40 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -137,6 +137,11 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
                 return 1;
 
         /*
+         * Make sure the device is in D0 state.
+         */
+        uart_change_pm(state, UART_PM_STATE_ON);
+
+        /*
          * Initialise and allocate the transmit and temporary
          * buffer.
          */
@@ -825,25 +830,29 @@ static int uart_set_info(struct tty_struct *tty, struct tty_port *port,
                  * If we fail to request resources for the
                  * new port, try to restore the old settings.
                  */
-                if (retval && old_type != PORT_UNKNOWN) {
+                if (retval) {
                         uport->iobase = old_iobase;
                         uport->type = old_type;
                         uport->hub6 = old_hub6;
                         uport->iotype = old_iotype;
                         uport->regshift = old_shift;
                         uport->mapbase = old_mapbase;
-                        retval = uport->ops->request_port(uport);
-                        /*
-                         * If we failed to restore the old settings,
-                         * we fail like this.
-                         */
-                        if (retval)
-                                uport->type = PORT_UNKNOWN;
 
-                        /*
-                         * We failed anyway.
-                         */
-                        retval = -EBUSY;
+                        if (old_type != PORT_UNKNOWN) {
+                                retval = uport->ops->request_port(uport);
+                                /*
+                                 * If we failed to restore the old settings,
+                                 * we fail like this.
+                                 */
+                                if (retval)
+                                        uport->type = PORT_UNKNOWN;
+
+                                /*
+                                 * We failed anyway.
+                                 */
+                                retval = -EBUSY;
+                        }
+
                         /* Added to return the correct error -Ram Gupta */
                         goto exit;
                 }
@@ -1571,12 +1580,6 @@ static int uart_open(struct tty_struct *tty, struct file *filp)
         }
 
         /*
-         * Make sure the device is in D0 state.
-         */
-        if (port->count == 1)
-                uart_change_pm(state, UART_PM_STATE_ON);
-
-        /*
          * Start up the serial port.
          */
         retval = uart_startup(tty, state, 0);