serial_core: Handle TIOC[GS]RS485 ioctls.

The following drivers: 8250_core, atmel_serial, max310x, mcf, omap-serial
and sci16is7xx implement code to handle RS485 ioctls.

In order to avoid code duplication, we implement a simple ioctl handler
on the serial_core layer.

This handler can be used by all the other drivers instead of duplicating
code.

Until this is the only RS485 ioctl handler, it will try first the
rs485_config callback and if it is not present it will call the driver
specific ioctl.
Reviewed-by: Alan Cox <alan@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial_core.c

@@ -1152,6 +1152,39 @@ static int uart_get_icount(struct tty_struct *tty,
 	return 0;
 }
 
+static int uart_get_rs485_config(struct uart_port *port,
+			 struct serial_rs485 __user *rs485)
+{
+	if (!port->rs485_config)
+		return -ENOIOCTLCMD;
+
+	if (copy_to_user(rs485, &port->rs485, sizeof(port->rs485)))
+		return -EFAULT;
+	return 0;
+}
+
+static int uart_set_rs485_config(struct uart_port *port,
+			 struct serial_rs485 __user *rs485_user)
+{
+	struct serial_rs485 rs485;
+	int ret;
+
+	if (!port->rs485_config)
+		return -ENOIOCTLCMD;
+
+	if (copy_from_user(&rs485, rs485_user, sizeof(*rs485_user)))
+		return -EFAULT;
+
+	ret = port->rs485_config(port, &rs485);
+	if (ret)
+		return ret;
+
+	if (copy_to_user(rs485_user, &port->rs485, sizeof(port->rs485)))
+		return -EFAULT;
+
+	return 0;
+}
+
 /*
  * Called via sys_ioctl.  We can use spin_lock_irq() here.
  */
@@ -1223,6 +1256,18 @@ uart_ioctl(struct tty_struct *tty, unsigned int cmd,
 	 * protected against the tty being hung up.
 	 */
 	switch (cmd) {
+	case TIOCGRS485:
+		ret = uart_get_rs485_config(state->uart_port, uarg);
+		break;
+
+	case TIOCSRS485:
+		ret = uart_set_rs485_config(state->uart_port, uarg);
+		break;
+	}
+	if (ret != -ENOIOCTLCMD)
+		goto out;
+
+	switch (cmd) {
 	case TIOCSERGETLSR: /* Get line status register */
 		ret = uart_get_lsr_info(tty, state, uarg);
 		break;

include/linux/serial_core.h

@@ -131,6 +131,8 @@ struct uart_port {
 	void			(*pm)(struct uart_port *, unsigned int state,
 				      unsigned int old);
 	void			(*handle_break)(struct uart_port *);
+	int			(*rs485_config)(struct uart_port *,
+						struct serial_rs485 *rs485);
 	unsigned int		irq;			/* irq number */
 	unsigned long		irqflags;		/* irq flags  */
 	unsigned int		uartclk;		/* base uart clock */
@@ -231,6 +233,7 @@ struct uart_port {
 	unsigned char		unused[2];
 	struct attribute_group	*attr_group;		/* port specific attributes */
 	const struct attribute_group **tty_groups;	/* all attributes (serial core use only) */
+	struct serial_rs485     rs485;
 	void			*private_data;		/* generic platform data pointer */
 };