[PATCH 3/4] serial: imx: Add support for rs485 RX_DURING_TX GPIO

[Christoph Niedermaier]

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 at dh-electronics.com>
---
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Cc: Jiri Slaby <jirislaby at kernel.org>
Cc: Shawn Guo <shawnguo at kernel.org>
Cc: Sascha Hauer <s.hauer at pengutronix.de>
Cc: Pengutronix Kernel Team <kernel at pengutronix.de>
Cc: Fabio Estevam <festevam at denx.de>
Cc: Marek Vasut <marex at denx.de>
Cc: Linux Team <linux-imx at nxp.com>
To: linux-serial at vger.kernel.org
To: linux-arm-kernel at lists.infradead.org
---
 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 05b432dc7a85..16f8baaf4f12 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;
 		}
@@ -697,7 +698,8 @@ 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;
@@ -1931,6 +1933,13 @@ 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