[PATCH v3 1/6] serial: Do not hold the port lock when setting rx-during-tx GPIO

[Lino Sanfilippo]

Both the imx and stm32 driver set the rx-during-tx GPIO in the
rs485_config() function by means of gpiod_set_value(). Since rs485_config()
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 setting the GPIO outside of the port lock in the serial
core and by using gpiod_set_value_cansleep() instead of gpiod_set_value().

Since now both the term and the rx-during-tx GPIO are set within the serial
core use a common function uart_set_rs485_gpios() to set both.

With moving it into the serial core setting the rx-during-tx GPIO is now
automatically done for all drivers that support such a GPIO.

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: stable@xxxxxxxxxxxxxxx
Signed-off-by: Lino Sanfilippo <l.sanfilippo@xxxxxxxxxx>
---
 drivers/tty/serial/imx.c         |  4 ----
 drivers/tty/serial/serial_core.c | 10 ++++++----
 drivers/tty/serial/stm32-usart.c |  5 +----
 3 files changed, 7 insertions(+), 12 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 13cb78340709..edb2ec6a5567 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -1947,10 +1947,6 @@ 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 7bdc21d5e13b..ef0500be3553 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1391,14 +1391,16 @@ static void uart_sanitize_serial_rs485(struct uart_port *port, struct serial_rs4
 	memset(rs485->padding1, 0, sizeof(rs485->padding1));
 }
 
-static void uart_set_rs485_termination(struct uart_port *port,
-				       const struct serial_rs485 *rs485)
+static void uart_set_rs485_gpios(struct uart_port *port,
+				 const struct serial_rs485 *rs485)
 {
 	if (!(rs485->flags & SER_RS485_ENABLED))
 		return;
 
 	gpiod_set_value_cansleep(port->rs485_term_gpio,
 				 !!(rs485->flags & SER_RS485_TERMINATE_BUS));
+	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)
@@ -1407,7 +1409,7 @@ static int uart_rs485_config(struct uart_port *port)
 	int ret;
 
 	uart_sanitize_serial_rs485(port, rs485);
-	uart_set_rs485_termination(port, rs485);
+	uart_set_rs485_gpios(port, rs485);
 
 	ret = port->rs485_config(port, NULL, rs485);
 	if (ret)
@@ -1449,7 +1451,7 @@ static int uart_set_rs485_config(struct tty_struct *tty, struct uart_port *port,
 	if (ret)
 		return ret;
 	uart_sanitize_serial_rs485(port, &rs485);
-	uart_set_rs485_termination(port, &rs485);
+	uart_set_rs485_gpios(port, &rs485);
 
 	spin_lock_irqsave(&port->lock, flags);
 	ret = port->rs485_config(port, &tty->termios, &rs485);
diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 5e9cf0c48813..8eb13bf055f2 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) {
-- 
2.40.1