[PATCH V3 3/4] serial: imx: Add support for RS485 RX_DURING_TX output GPIO

[Christoph Niedermaier <cniedermaier@dh-electronics.com>]

If a RX_DURING_TX GPIO is defined by the DT property "rs485-rx-during-tx-gpios"
this patch switches this GPIO accordingly to the RS485 flag RX_DURING_TX in user
space. In addition, the i.MX UART receiver is no longer turned on and off during
sending, because now the hardware is responsible for connecting or disconnecting
RX during TX controlled by this GPIO.

Signed-off-by: Christoph Niedermaier <cniedermaier@dh-electronics.com>
---
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Pengutronix Kernel Team <kernel@pengutronix.de>
Cc: Alexander Dahl <ada@thorsis.com>
Cc: Fabio Estevam <festevam@denx.de>
Cc: Marek Vasut <marex@denx.de>
Cc: kernel@dh-electronics.com
Cc: Linux Team <linux-imx@nxp.com>
To: linux-serial@vger.kernel.org
To: linux-arm-kernel@lists.infradead.org
---
V2: - Rework of the commit message
V3: - No changes
---
 drivers/tty/serial/imx.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 757825edb0cd..f241f16472f2 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -476,7 +476,8 @@ static void imx_uart_stop_tx(struct uart_port *port)
 				imx_uart_rts_inactive(sport, &ucr2);
 			imx_uart_writel(sport, ucr2, UCR2);
 
-			imx_uart_start_rx(port);
+			if (!port->rs485_rx_during_tx_gpio)
+				imx_uart_start_rx(port);
 
 			sport->tx_state = OFF;
 		}
@@ -705,7 +706,8 @@ static void imx_uart_start_tx(struct uart_port *port)
 				imx_uart_rts_inactive(sport, &ucr2);
 			imx_uart_writel(sport, ucr2, UCR2);
 
-			if (!(port->rs485.flags & SER_RS485_RX_DURING_TX))
+			if (!(port->rs485.flags & SER_RS485_RX_DURING_TX) &&
+			    !port->rs485_rx_during_tx_gpio)
 				imx_uart_stop_rx(port);
 
 			sport->tx_state = WAIT_AFTER_RTS;
@@ -1955,6 +1957,13 @@ static int imx_uart_rs485_config(struct uart_port *port, struct ktermios *termio
 	    rs485conf->flags & SER_RS485_RX_DURING_TX)
 		imx_uart_start_rx(port);
 
+	if (port->rs485_rx_during_tx_gpio) {
+		if (rs485conf->flags & SER_RS485_RX_DURING_TX)
+			gpiod_set_value_cansleep(port->rs485_rx_during_tx_gpio, 1);
+		else
+			gpiod_set_value_cansleep(port->rs485_rx_during_tx_gpio, 0);
+	}
+
 	return 0;
 }
 
-- 
2.11.0