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>

3 files changed, 15 insertions, 6 deletions

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index aca3b7dbd09c..d2c7d88d5774 100644
--- a/drivers/tty/serial/imx.c
+++ b/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);
 
diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index 227347548fff..56e683373d6d 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/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);
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index a59184a7afb0..f57969de2f1c 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/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);