serial: imx: Fix the RTS GPIO polarity in RS485 mode

On a board that needs to drive RTS GPIO high in order to enable the
transmission of a RS485 transceiver the following description is
passed in the devide tree:

&uart4 {
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_uart4>;
        rts-gpios = <&gpio6 2 GPIO_ACTIVE_HIGH>;
        status = "okay";
};

and userspace configures the uart port as follows:

/* enable RS485 mode: */
rs485conf.flags |= SER_RS485_ENABLED;

/* set logical level for RTS pin equal to 1 when sending: */
rs485conf.flags |= SER_RS485_RTS_ON_SEND;

/* set logical level for RTS pin equal to 0 after sending: */
rs485conf.flags &= ~(SER_RS485_RTS_AFTER_SEND);

However the RTS GPIO polarity observed in the oscilloscope is inverted.

When the SER_RS485_RTS_ON_SEND flag is set the imx_port_rts_active()
function should be called and following the same logic when
SER_RS485_RTS_AFTER_SEND flag is cleared the imx_port_rts_inactive()
should be called.

Do such logic change so that RS485 communication in half duplex can
work successfully when the RTS GPIO pin is passed via device tree.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

@@ -377,9 +377,9 @@ static void imx_stop_tx(struct uart_port *port)
 	    readl(port->membase + USR2) & USR2_TXDC) {
 		temp = readl(port->membase + UCR2);
 		if (port->rs485.flags & SER_RS485_RTS_AFTER_SEND)
-			imx_port_rts_inactive(sport, &temp);
-		else
 			imx_port_rts_active(sport, &temp);
+		else
+			imx_port_rts_inactive(sport, &temp);
 		temp |= UCR2_RXEN;
 		writel(temp, port->membase + UCR2);
 
@@ -585,9 +585,9 @@ static void imx_start_tx(struct uart_port *port)
 	if (port->rs485.flags & SER_RS485_ENABLED) {
 		temp = readl(port->membase + UCR2);
 		if (port->rs485.flags & SER_RS485_RTS_ON_SEND)
-			imx_port_rts_inactive(sport, &temp);
-		else
 			imx_port_rts_active(sport, &temp);
+		else
+			imx_port_rts_inactive(sport, &temp);
 		if (!(port->rs485.flags & SER_RS485_RX_DURING_TX))
 			temp &= ~UCR2_RXEN;
 		writel(temp, port->membase + UCR2);
@@ -1477,9 +1477,9 @@ imx_set_termios(struct uart_port *port, struct ktermios *termios,
 				 */
 				if (port->rs485.flags &
 				    SER_RS485_RTS_AFTER_SEND)
-					imx_port_rts_inactive(sport, &ucr2);
-				else
 					imx_port_rts_active(sport, &ucr2);
+				else
+					imx_port_rts_inactive(sport, &ucr2);
 			} else {
 				imx_port_rts_auto(sport, &ucr2);
 			}
@@ -1489,9 +1489,9 @@ imx_set_termios(struct uart_port *port, struct ktermios *termios,
 	} else if (port->rs485.flags & SER_RS485_ENABLED) {
 		/* disable transmitter */
 		if (port->rs485.flags & SER_RS485_RTS_AFTER_SEND)
-			imx_port_rts_inactive(sport, &ucr2);
-		else
 			imx_port_rts_active(sport, &ucr2);
+		else
+			imx_port_rts_inactive(sport, &ucr2);
 	}
 
 
@@ -1733,9 +1733,9 @@ static int imx_rs485_config(struct uart_port *port,
 		/* disable transmitter */
 		temp = readl(sport->port.membase + UCR2);
 		if (rs485conf->flags & SER_RS485_RTS_AFTER_SEND)
-			imx_port_rts_inactive(sport, &temp);
-		else
 			imx_port_rts_active(sport, &temp);
+		else
+			imx_port_rts_inactive(sport, &temp);
 		writel(temp, sport->port.membase + UCR2);
 	}