tty: serial - fix tty referencing in set_ldisc

Pass down the ldisc number so that the drivers don't have to peek into the
tty object themselves. This lets us get rid of another case of back referencing
port to tty which we don't want (because of races versus hangup/close).
Signed-off-by: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/serial/bfin_5xx.c

@@ -957,15 +957,12 @@ bfin_serial_verify_port(struct uart_port *port, struct serial_struct *ser)
  * Enable the IrDA function if tty->ldisc.num is N_IRDA.
  * In other cases, disable IrDA function.
  */
-static void bfin_serial_set_ldisc(struct uart_port *port)
+static void bfin_serial_set_ldisc(struct uart_port *port, int ld)
 {
 	int line = port->line;
 	unsigned short val;
 
-	if (line >= port->state->port.tty->driver->num)
-		return;
-
-	switch (port->state->port.tty->termios->c_line) {
+	switch (ld) {
 	case N_IRDA:
 		val = UART_GET_GCTL(&bfin_serial_ports[line]);
 		val |= (IREN | RPOLC);

drivers/serial/serial_core.c

@@ -1194,7 +1194,7 @@ static void uart_set_ldisc(struct tty_struct *tty)
 	struct uart_port *uport = state->uart_port;
 
 	if (uport->ops->set_ldisc)
-		uport->ops->set_ldisc(uport);
+		uport->ops->set_ldisc(uport, tty->termios->c_line);
 }
 
 static void uart_set_termios(struct tty_struct *tty,

include/linux/serial_core.h

@@ -220,7 +220,7 @@ struct uart_ops {
 	void		(*flush_buffer)(struct uart_port *);
 	void		(*set_termios)(struct uart_port *, struct ktermios *new,
 				       struct ktermios *old);
-	void		(*set_ldisc)(struct uart_port *);
+	void		(*set_ldisc)(struct uart_port *, int new);
 	void		(*pm)(struct uart_port *, unsigned int state,
 			      unsigned int oldstate);
 	int		(*set_wake)(struct uart_port *, unsigned int state);