serial: core: Support common rs485 binding for RTS polarity

When a driver invokes the uart_get_rs485_mode() helper, set the RTS
polarity to active high by default unless the newly introduced
"rs485-rts-active-low" property was specified.

imx contains a line to set the default RTS polarity to active high,
it is now superfluous and hence deleted.

omap-serial historically defaults to active low and supports an
"rs485-rts-active-high" property to inverse the polarity.
Retain that behavior for compatibility.

Cc: Mark Jackson <mpfj@newflow.co.uk>
Cc: Michał Oleszczyk <oleszczyk.m@gmail.com>
Cc: Rafael Gago Castano <rgc@hms.se>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

@@ -2060,7 +2060,6 @@ static int serial_imx_probe(struct platform_device *pdev)
 	sport->port.fifosize = 32;
 	sport->port.ops = &imx_pops;
 	sport->port.rs485_config = imx_rs485_config;
-	sport->port.rs485.flags |= SER_RS485_RTS_ON_SEND;
 	sport->port.flags = UPF_BOOT_AUTOCONF;
 	timer_setup(&sport->timer, imx_timeout, 0);
 

drivers/tty/serial/omap-serial.c

@@ -1613,10 +1613,13 @@ static int serial_omap_probe_rs485(struct uart_omap_port *up,
 
 	uart_get_rs485_mode(up->dev, rs485conf);
 
-	if (of_property_read_bool(np, "rs485-rts-active-high"))
+	if (of_property_read_bool(np, "rs485-rts-active-high")) {
 		rs485conf->flags |= SER_RS485_RTS_ON_SEND;
-	else
+		rs485conf->flags &= ~SER_RS485_RTS_AFTER_SEND;
+	} else {
+		rs485conf->flags &= ~SER_RS485_RTS_ON_SEND;
 		rs485conf->flags |= SER_RS485_RTS_AFTER_SEND;
+	}
 
 	/* check for tx enable gpio */
 	up->rts_gpio = of_get_named_gpio_flags(np, "rts-gpio", 0, &flags);

drivers/tty/serial/serial_core.c

@@ -3036,16 +3036,23 @@ void uart_get_rs485_mode(struct device *dev, struct serial_rs485 *rs485conf)
 	}
 
 	/*
-	 * clear full-duplex and enabled flags to get to a defined state with
-	 * the two following properties.
+	 * Clear full-duplex and enabled flags, set RTS polarity to active high
+	 * to get to a defined state with the following properties:
 	 */
-	rs485conf->flags &= ~(SER_RS485_RX_DURING_TX | SER_RS485_ENABLED);
+	rs485conf->flags &= ~(SER_RS485_RX_DURING_TX | SER_RS485_ENABLED |
+			      SER_RS485_RTS_AFTER_SEND);
+	rs485conf->flags |= SER_RS485_RTS_ON_SEND;
 
 	if (device_property_read_bool(dev, "rs485-rx-during-tx"))
 		rs485conf->flags |= SER_RS485_RX_DURING_TX;
 
 	if (device_property_read_bool(dev, "linux,rs485-enabled-at-boot-time"))
 		rs485conf->flags |= SER_RS485_ENABLED;
+
+	if (device_property_read_bool(dev, "rs485-rts-active-low")) {
+		rs485conf->flags &= ~SER_RS485_RTS_ON_SEND;
+		rs485conf->flags |= SER_RS485_RTS_AFTER_SEND;
+	}
 }
 EXPORT_SYMBOL_GPL(uart_get_rs485_mode);