From: Matthias Fuchs<redacted>

Some Exar UARTs support an auto rs485 mode. In this mode
the UART's RTS# pin is activated during transmitting and
can be used to enable a rs485 line driver. This has nothing
to do with attempts to do this by manually asserting/
deasserting handshake lines in software.

Signed-off-by: Matthias Fuchs<redacted>

[wsa] Replaced 0xbf with define, saved some line-breaks.

Signed-off-by: Wolfram Sang<redacted>
---
  drivers/tty/serial/8250.c  |   68 ++++++++++++++++++++++++++++++++++++++++++++
  include/linux/serial_reg.h |    1 +
  2 files changed, 69 insertions(+), 0 deletions(-)

diff --git a/drivers/tty/serial/8250.c b/drivers/tty/serial/8250.c
index f8f2320..920b4df 100644
--- a/drivers/tty/serial/8250.c
+++ b/drivers/tty/serial/8250.c

@@ -38,6 +38,7 @@
  #include<linux/nmi.h>
  #include<linux/mutex.h>
  #include<linux/slab.h>
+#include<linux/uaccess.h>

  #include<asm/io.h>
  #include<asm/irq.h>

@@ -2698,6 +2699,72 @@ serial8250_type(struct uart_port *port)
  	return uart_config[type].name;
  }

+static int serial8250_ioctl_port(struct uart_port *port,
+		      unsigned int cmd, unsigned long arg)
+{
+	struct uart_8250_port *up = (struct uart_8250_port *)port;
+	unsigned long flags;
+
+	switch (cmd) {
+	case TIOCSRS485:
+	{
+		struct serial_rs485 rs485ctrl;
+		unsigned char fctr, lcr;
+
+		if (port->type != PORT_16850)
+			return -ENOTTY;
+
+		if (copy_from_user(&rs485ctrl, (struct serial_rs485 *)arg,
+				   sizeof(rs485ctrl)))
+			return -EFAULT;
+
+		spin_lock_irqsave(&up->port.lock, flags);
+		lcr = serial_inp(up, UART_LCR);
+		serial_outp(up, UART_LCR, UART_LCR_CONF_MODE_B);
+		fctr = serial_inp(up, UART_FCTR);
+		if (rs485ctrl.flags&  SER_RS485_ENABLED)
+			fctr |= UART_FCTR_RS485;
+		else
+			fctr&= ~UART_FCTR_RS485;
+		serial_outp(up, UART_FCTR, fctr);
+		serial_outp(up, UART_LCR, lcr);
+		spin_unlock_irqrestore(&up->port.lock, flags);
+		return 0;
+	}
+
+	case TIOCGRS485:
+	{
+		struct serial_rs485 rs485ctrl;
+		unsigned char lcr;
+
+		if (port->type != PORT_16850)
+			return -ENOTTY;
+
+		memset(&rs485ctrl, 0, sizeof(rs485ctrl));
+
+		spin_lock_irqsave(&up->port.lock, flags);
+		lcr = serial_inp(up, UART_LCR);
+		serial_outp(up, UART_LCR, UART_LCR_CONF_MODE_B);
+		if (serial_inp(up, UART_FCTR)&  UART_FCTR_RS485)
+			rs485ctrl.flags = SER_RS485_ENABLED;
+		else
+			rs485ctrl.flags = 0;