linux-kernel - [PATCH 2/8] serial: core, 8250: set RS485 termination gpio in serial core

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Date:   Wed, 22 Jun 2022 17:46:53 +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 2/8] 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.

This 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 3e3d784aa628..5245c179cc51 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -675,9 +675,6 @@ int serial8250_em485_config(struct uart_port *port, struct serial_rs485 *rs485)
 		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 015f4e1da647..b387376e6fa2 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1352,12 +1352,23 @@ static void uart_sanitize_serial_rs485(struct uart_port *port, struct serial_rs4
 	memset(rs485->padding, 0, sizeof(rs485->padding));
 }
 
+static void uart_set_rs485_termination(struct uart_port *port,
+				       const struct serial_rs485 *rs485)
+{
+	if (!port->rs485_term_gpio || !(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, rs485);
 	if (ret)
@@ -1400,6 +1411,7 @@ static int uart_set_rs485_config(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, &rs485);
-- 
2.36.1