[PATCH V4 2/4] serial: core: Add option to output RS485 RX_DURING_TX state via GPIO

[Christoph Niedermaier]

This patch provides a generic GPIO variable for outputting the state
of RS485 RX_DURING_TX. The GPIO is defined by the devicetree property
"rs485-rx-during-tx-gpios". To use it in a low level serial driver,
the evaluation of this variable must be implemented there accordingly.

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: Alexander Dahl <ada at thorsis.com>
Cc: Marek Vasut <marex at denx.de>
Cc: kernel at dh-electronics.com
Cc: Linux Team <linux-imx at nxp.com>
To: linux-serial at vger.kernel.org
To: linux-arm-kernel at lists.infradead.org
---
V2: - Rework of the commit message
    - Rework GPIO property comment
V3: - Rework GPIO property comment
V4: - No changes
---
 drivers/tty/serial/serial_core.c | 12 ++++++++++++
 include/linux/serial_core.h      |  1 +
 2 files changed, 13 insertions(+)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index b9fbbee598b8..867f2675caca 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -3410,6 +3410,7 @@ int uart_get_rs485_mode(struct uart_port *port)
 	struct device *dev = port->dev;
 	u32 rs485_delay[2];
 	int ret;
+	int rx_during_tx_gpio_flag;
 
 	ret = device_property_read_u32_array(dev, "rs485-rts-delay",
 					     rs485_delay, 2);
@@ -3458,6 +3459,17 @@ int uart_get_rs485_mode(struct uart_port *port)
 	if (port->rs485_term_gpio)
 		port->rs485_supported.flags |= SER_RS485_TERMINATE_BUS;
 
+	rx_during_tx_gpio_flag = (rs485conf->flags & SER_RS485_RX_DURING_TX) ?
+				 GPIOD_OUT_HIGH : GPIOD_OUT_LOW;
+	port->rs485_rx_during_tx_gpio = devm_gpiod_get_optional(dev,
+								"rs485-rx-during-tx",
+								rx_during_tx_gpio_flag);
+	if (IS_ERR(port->rs485_rx_during_tx_gpio)) {
+		ret = PTR_ERR(port->rs485_rx_during_tx_gpio);
+		port->rs485_rx_during_tx_gpio = NULL;
+		return dev_err_probe(dev, ret, "Cannot get rs485-rx-during-tx-gpios\n");
+	}
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(uart_get_rs485_mode);
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index fd59f600094a..7d3784b18a6f 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -579,6 +579,7 @@ struct uart_port {
 	struct serial_rs485     rs485;
 	struct serial_rs485	rs485_supported;	/* Supported mask for serial_rs485 */
 	struct gpio_desc	*rs485_term_gpio;	/* enable RS485 bus termination */
+	struct gpio_desc	*rs485_rx_during_tx_gpio; /* Output GPIO that sets the state of RS485 RX during TX */
 	struct serial_iso7816   iso7816;
 	void			*private_data;		/* generic platform data pointer */
 };
-- 
2.11.0