linux-kernel - [PATCH v4 3/8] serial: core, 8250: set RS485 termination GPIO in serial core

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Date:   Sun, 10 Jul 2022 18:44:37 +0200
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     gregkh@...uxfoundation.org, jirislaby@...nel.org
Cc:     ilpo.jarvinen@...ux.intel.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org,
        andriy.shevchenko@...ux.intel.com, vz@...ia.com,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        lukas@...ner.de, p.rosenberger@...bus.com,
        Lino Sanfilippo <l.sanfilippo@...bus.com>
Subject: [PATCH v4 3/8] serial: core, 8250: set RS485 termination GPIO in serial core

From: Lino Sanfilippo <l.sanfilippo@...bus.com>

In serial8250_em485_config() the termination GPIO is set with the uart_port
spinlock held. This is an issue if setting the GPIO line can sleep (e.g.
since the concerning GPIO expander is connected via SPI or I2C).

Fix this by setting the termination line outside of the uart_port spinlock
in the serial core and using gpiod_set_value_cansleep() which instead of
gpiod_set_value() allows it to sleep.

Beside fixing the termination GPIO line setting for the 8250 driver this
change also makes setting the termination GPIO generic for all UART
drivers.

Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
---
 drivers/tty/serial/8250/8250_port.c |  3 ---
 drivers/tty/serial/serial_core.c    | 12 ++++++++++++
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index ed2a606f2da7..72252d956f17 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -676,9 +676,6 @@ int serial8250_em485_config(struct uart_port *port, struct ktermios *termios,
 		rs485->flags &= ~SER_RS485_RTS_AFTER_SEND;
 	}
 
-	gpiod_set_value(port->rs485_term_gpio,
-			rs485->flags & SER_RS485_TERMINATE_BUS);
-
 	/*
 	 * Both serial8250_em485_init() and serial8250_em485_destroy()
 	 * are idempotent.
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 1db44cde76f6..047ec51dbd41 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1358,12 +1358,23 @@ 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)
+{
+	if (!(rs485->flags & SER_RS485_ENABLED))
+		return;
+
+	gpiod_set_value_cansleep(port->rs485_term_gpio,
+				 !!(rs485->flags & SER_RS485_TERMINATE_BUS));
+}
+
 int uart_rs485_config(struct uart_port *port)
 {
 	struct serial_rs485 *rs485 = &port->rs485;
 	int ret;
 
 	uart_sanitize_serial_rs485(port, rs485);
+	uart_set_rs485_termination(port, rs485);
 
 	ret = port->rs485_config(port, NULL, rs485);
 	if (ret)
@@ -1406,6 +1417,7 @@ 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);
 
 	spin_lock_irqsave(&port->lock, flags);
 	ret = port->rs485_config(port, &tty->termios, &rs485);
-- 
2.25.1