linux-kernel - [PATCH v4 4/6] serial: 8250: set rx-enable gpio state when rs485 is disabled

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Message-Id: <20240126-dev-rx-enable-v4-4-45aaf4d96328@theobroma-systems.com>
Date: Fri, 26 Jan 2024 15:55:13 +0100
From: Farouk Bouabid <farouk.bouabid@...obroma-systems.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
 Jiri Slaby <jirislaby@...nel.org>, Rob Herring <robh+dt@...nel.org>, 
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, 
 Conor Dooley <conor+dt@...nel.org>, Heiko Stuebner <heiko@...ech.de>
Cc: Rob Herring <robh@...nel.org>, linux-kernel@...r.kernel.org, 
 linux-serial@...r.kernel.org, devicetree@...r.kernel.org, 
 linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org, 
 quentin.schulz@...obroma-systems.com, 
 Farouk Bouabid <farouk.bouabid@...obroma-systems.com>
Subject: [PATCH v4 4/6] serial: 8250: set rx-enable gpio state when rs485
 is disabled

Add the possibility to de-activate rx-enable gpio when rs485 is disabled.
This defines the state of RE or DE/RE signal when em485 is disabled.

Signed-off-by: Farouk Bouabid <farouk.bouabid@...obroma-systems.com>
---
 drivers/tty/serial/8250/8250_port.c | 4 ++++
 drivers/tty/serial/serial_core.c    | 6 ++++++
 include/linux/serial_core.h         | 1 +
 3 files changed, 11 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 54d8f809b81e..fbd0212d2397 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -582,12 +582,16 @@ static int serial8250_em485_init(struct uart_8250_port *p)
  */
 void serial8250_em485_destroy(struct uart_8250_port *p)
 {
+	struct uart_port *port = &p->port;
+
 	if (!p->em485)
 		return;
 
 	hrtimer_cancel(&p->em485->start_tx_timer);
 	hrtimer_cancel(&p->em485->stop_tx_timer);
 
+	gpiod_set_value(port->rs485_re_gpio, !port->rs485_re_gpio_inactive_when_rs485_disabled);
+
 	kfree(p->em485);
 	p->em485 = NULL;
 }
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 47aeece985f3..6460646cf83c 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -3663,6 +3663,12 @@ int uart_get_rs485_mode(struct uart_port *port)
 	if (port->rs485_rx_during_tx_gpio)
 		port->rs485_supported.flags |= SER_RS485_RX_DURING_TX;
 
+	port->rs485_re_gpio_inactive_when_rs485_disabled = device_property_read_bool(dev,
+		"rs485-rx-enable-inactive-when-rs485-disabled");
+
+	port->rs485_re_gpio = devm_gpiod_get_optional(dev, "rs485-rx-enable",
+		port->rs485_re_gpio_inactive_when_rs485_disabled ? GPIOD_OUT_LOW : GPIOD_OUT_HIGH);
+
 	if (IS_ERR(port->rs485_re_gpio)) {
 		ret = PTR_ERR(port->rs485_re_gpio);
 		port->rs485_re_gpio = NULL;
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 364583203a24..fa5a92b56360 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -585,6 +585,7 @@ struct uart_port {
 	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 gpio_desc	*rs485_re_gpio;		/* gpio RS485 receive enable */
+	bool	rs485_re_gpio_inactive_when_rs485_disabled;
 	struct serial_iso7816   iso7816;
 	void			*private_data;		/* generic platform data pointer */
 };

-- 
2.34.1