linux-kernel - [PATCH v8 1/7] serial: Do not hold the port lock when setting rx-during-tx GPIO

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Date: Fri,  5 Jan 2024 15:11:47 +0100
From: Lino Sanfilippo <l.sanfilippo@...bus.com>
To: gregkh@...uxfoundation.org,
	jirislaby@...nel.org,
	ilpo.jarvinen@...ux.intel.com
Cc: u.kleine-koenig@...gutronix.de,
	shawnguo@...nel.org,
	s.hauer@...gutronix.de,
	mcoquelin.stm32@...il.com,
	alexandre.torgue@...s.st.com,
	cniedermaier@...electronics.com,
	hugo@...ovil.com,
	m.brock@...mierlo.com,
	linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org,
	LinoSanfilippo@....de,
	lukas@...ner.de,
	p.rosenberger@...bus.com,
	Lino Sanfilippo <l.sanfilippo@...bus.com>,
	stable@...r.kernel.org
Subject: [PATCH v8 1/7] serial: Do not hold the port lock when setting rx-during-tx GPIO

Both the imx and stm32 driver set the rx-during-tx GPIO in rs485_config().
Since this function is called with the port lock held, this can be an
problem in case that setting the GPIO line can sleep (e.g. if a GPIO
expander is used which is connected via SPI or I2C).

Avoid this issue by moving the GPIO setting outside of the port lock into
the serial core and thus making it a generic feature.

Also reset old GPIO settings in case that changing the RS485 configuration
failed.

Fixes: c54d48543689 ("serial: stm32: Add support for rs485 RX_DURING_TX output GPIO")
Fixes: ca530cfa968c ("serial: imx: Add support for RS485 RX_DURING_TX output GPIO")
Cc: Shawn Guo <shawnguo@...nel.org>
Cc: Sascha Hauer <s.hauer@...gutronix.de>
Cc: stable@...r.kernel.org
Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
---
 drivers/tty/serial/imx.c         |  4 ----
 drivers/tty/serial/serial_core.c | 26 ++++++++++++++++++++++++--
 drivers/tty/serial/stm32-usart.c |  5 +----
 3 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 708b9852a575..9cffeb23112b 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -1943,10 +1943,6 @@ 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)
-		gpiod_set_value_cansleep(port->rs485_rx_during_tx_gpio,
-					 !!(rs485conf->flags & SER_RS485_RX_DURING_TX));
-
 	return 0;
 }
 
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index f1348a509552..d155131f221d 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1402,6 +1402,16 @@ static void uart_set_rs485_termination(struct uart_port *port,
 				 !!(rs485->flags & SER_RS485_TERMINATE_BUS));
 }
 
+static void uart_set_rs485_rx_during_tx(struct uart_port *port,
+					const struct serial_rs485 *rs485)
+{
+	if (!(rs485->flags & SER_RS485_ENABLED))
+		return;
+
+	gpiod_set_value_cansleep(port->rs485_rx_during_tx_gpio,
+				 !!(rs485->flags & SER_RS485_RX_DURING_TX));
+}
+
 static int uart_rs485_config(struct uart_port *port)
 {
 	struct serial_rs485 *rs485 = &port->rs485;
@@ -1413,12 +1423,17 @@ static int uart_rs485_config(struct uart_port *port)
 
 	uart_sanitize_serial_rs485(port, rs485);
 	uart_set_rs485_termination(port, rs485);
+	uart_set_rs485_rx_during_tx(port, rs485);
 
 	uart_port_lock_irqsave(port, &flags);
 	ret = port->rs485_config(port, NULL, rs485);
 	uart_port_unlock_irqrestore(port, flags);
-	if (ret)
+	if (ret) {
 		memset(rs485, 0, sizeof(*rs485));
+		/* unset GPIOs */
+		gpiod_set_value_cansleep(port->rs485_term_gpio, 0);
+		gpiod_set_value_cansleep(port->rs485_rx_during_tx_gpio, 0);
+	}
 
 	return ret;
 }
@@ -1457,6 +1472,7 @@ static int uart_set_rs485_config(struct tty_struct *tty, struct uart_port *port,
 		return ret;
 	uart_sanitize_serial_rs485(port, &rs485);
 	uart_set_rs485_termination(port, &rs485);
+	uart_set_rs485_rx_during_tx(port, &rs485);
 
 	uart_port_lock_irqsave(port, &flags);
 	ret = port->rs485_config(port, &tty->termios, &rs485);
@@ -1468,8 +1484,14 @@ static int uart_set_rs485_config(struct tty_struct *tty, struct uart_port *port,
 			port->ops->set_mctrl(port, port->mctrl);
 	}
 	uart_port_unlock_irqrestore(port, flags);
-	if (ret)
+	if (ret) {
+		/* restore old GPIO settings */
+		gpiod_set_value_cansleep(port->rs485_term_gpio,
+			!!(port->rs485.flags & SER_RS485_TERMINATE_BUS));
+		gpiod_set_value_cansleep(port->rs485_rx_during_tx_gpio,
+			!!(port->rs485.flags & SER_RS485_RX_DURING_TX));
 		return ret;
+	}
 
 	if (copy_to_user(rs485_user, &port->rs485, sizeof(port->rs485)))
 		return -EFAULT;
diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 3048620315d6..ec9a72a5bea9 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -226,10 +226,7 @@ static int stm32_usart_config_rs485(struct uart_port *port, struct ktermios *ter
 
 	stm32_usart_clr_bits(port, ofs->cr1, BIT(cfg->uart_enable_bit));
 
-	if (port->rs485_rx_during_tx_gpio)
-		gpiod_set_value_cansleep(port->rs485_rx_during_tx_gpio,
-					 !!(rs485conf->flags & SER_RS485_RX_DURING_TX));
-	else
+	if (!port->rs485_rx_during_tx_gpio)
 		rs485conf->flags |= SER_RS485_RX_DURING_TX;
 
 	if (rs485conf->flags & SER_RS485_ENABLED) {
-- 
2.43.0