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serial_core: fix uart PORT_UNKNOWN handling

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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>
This commit is contained in:
Thomas Pfaff 2014-04-23 12:33:22 +02:00 committed by Greg Kroah-Hartman
parent f94b057268
commit 7deb39ed8d
1 changed files with 21 additions and 18 deletions
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39
drivers/tty/serial/serial_core.c
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@ -136,6 +136,11 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
if (uport->type == PORT_UNKNOWN)
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;
}
@ -1570,12 +1579,6 @@ static int uart_open(struct tty_struct *tty, struct file *filp)
goto err_dec_count;
}
/*
* 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.
*/