From 668375a1e77f69f1173d6bd9125e2ae8e101f75c Mon Sep 17 00:00:00 2001
From: Lino Sanfilippo <l.sanfilippo@kunbus.com>
Date: Wed, 3 Jan 2024 07:18:12 +0100
Subject: [PATCH] serial: Do not hold the port lock when setting rx-during-tx
 GPIO

References: bsc#1214683 (PREEMPT_RT prerequisite backports)
Patch-mainline: v6.6.15
Git-commit: 07c30ea5861fb26a77dade8cdc787252f6122fb1

commit 07c30ea5861fb26a77dade8cdc787252f6122fb1 upstream.

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 a
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 with commit c54d48543689 ("serial: stm32: Add support for rs485
RX_DURING_TX output GPIO") the SER_RS485_RX_DURING_TX flag is only set if a
rx-during-tx GPIO is _not_ available, which is wrong. Fix this, too.

Furthermore 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@kernel.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc:  <stable@vger.kernel.org>
Signed-off-by: Lino Sanfilippo <l.sanfilippo@kunbus.com>
Link: https://lore.kernel.org/r/20240103061818.564-2-l.sanfilippo@kunbus.com
Signed-off-by: Lino Sanfilippo <l.sanfilippo@kunbus.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 drivers/tty/serial/imx.c         |  4 ----
 drivers/tty/serial/serial_core.c | 26 ++++++++++++++++++++++++--
 drivers/tty/serial/stm32-usart.c |  8 ++------
 3 files changed, 26 insertions(+), 12 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index bb77a887c61c..7c79792c5a0b 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -1961,10 +1961,6 @@ 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 e45d453d1ab1..4c1844f7f798 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1415,6 +1415,16 @@ 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;
@@ -1426,12 +1436,17 @@ 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);
 
 	spin_lock_irqsave(&port->lock, flags);
 	ret = port->rs485_config(port, NULL, rs485);
 	spin_unlock_irqrestore(&port->lock, 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;
 }
@@ -1470,6 +1485,7 @@ 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);
 
 	spin_lock_irqsave(&port->lock, flags);
 	ret = port->rs485_config(port, &tty->termios, &rs485);
@@ -1481,8 +1497,14 @@ static int uart_set_rs485_config(struct tty_struct *tty, struct uart_port *port,
 			port->ops->set_mctrl(port, port->mctrl);
 	}
 	spin_unlock_irqrestore(&port->lock, 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 be47cd343cf6..111a4db22a26 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -226,12 +226,6 @@ 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
-		rs485conf->flags |= SER_RS485_RX_DURING_TX;
-
 	if (rs485conf->flags & SER_RS485_ENABLED) {
 		cr1 = readl_relaxed(port->membase + ofs->cr1);
 		cr3 = readl_relaxed(port->membase + ofs->cr3);
@@ -256,6 +250,8 @@ static int stm32_usart_config_rs485(struct uart_port *port, struct ktermios *ter
 
 		writel_relaxed(cr3, port->membase + ofs->cr3);
 		writel_relaxed(cr1, port->membase + ofs->cr1);
+
+		rs485conf->flags |= SER_RS485_RX_DURING_TX;
 	} else {
 		stm32_usart_clr_bits(port, ofs->cr3,
 				     USART_CR3_DEM | USART_CR3_DEP);