tty/serial: at91: RS485 mode: 0 is valid for delay_rts_after_send

commit 8687634b upstream.

In RS485 mode, we may want to set the delay_rts_after_send value to 0.
In the datasheet, the 0 value is said to "disable" the Transmitter Timeguard but
this is exactly the expected behavior if we want no delay...

Moreover, if the value was set to non-zero value by device-tree or earlier
ioctl command, it was impossible to change it back to zero.
Reported-by: Sami Pietikäinen <Sami.Pietikainen@wapice.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[ kamal: backport to 3.19-stable: context ]
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

drivers/tty/serial/atmel_serial.c

@@ -308,7 +308,6 @@ static int atmel_config_rs485(struct uart_port *port,
 	if (rs485conf->flags & SER_RS485_ENABLED) {
 		dev_dbg(port->dev, "Setting UART to RS485\n");
 		atmel_port->tx_done_mask = ATMEL_US_TXEMPTY;
-		if ((rs485conf->delay_rts_after_send) > 0)
 		UART_PUT_TTGR(port, rs485conf->delay_rts_after_send);
 		mode |= ATMEL_US_USMODE_RS485;
 	} else {
@@ -370,7 +369,6 @@ static void atmel_set_mctrl(struct uart_port *port, u_int mctrl)
 
 	if (port->rs485.flags & SER_RS485_ENABLED) {
 		dev_dbg(port->dev, "Setting UART to RS485\n");
-		if ((port->rs485.delay_rts_after_send) > 0)
 		UART_PUT_TTGR(port, port->rs485.delay_rts_after_send);
 		mode |= ATMEL_US_USMODE_RS485;
 	} else {
@@ -2026,7 +2024,6 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
 	mode &= ~ATMEL_US_USMODE;
 
 	if (port->rs485.flags & SER_RS485_ENABLED) {
-		if ((port->rs485.delay_rts_after_send) > 0)
 		UART_PUT_TTGR(port, port->rs485.delay_rts_after_send);
 		mode |= ATMEL_US_USMODE_RS485;
 	}