linux-kernel - [PATCH 5.10 273/530] serial: omap: dont disable rs485 if rts gpio is missing

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Date:   Wed, 12 May 2021 16:46:23 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dario Binacchi <dariobin@...ero.it>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.10 273/530] serial: omap: dont disable rs485 if rts gpio is missing

From: Dario Binacchi <dariobin@...ero.it>

[ Upstream commit 45f6b6db53c80787b79044629b062dfcf2da71ec ]

There are rs485 transceivers (e.g. MAX13487E/MAX13488E) which
automatically disable or enable the driver and receiver to keep the bus
in the correct state.
In these cases we don't need a GPIO for flow control.

Fixes: 4a0ac0f55b18 ("OMAP: add RS485 support")
Signed-off-by: Dario Binacchi <dariobin@...ero.it>
Link: https://lore.kernel.org/r/20210415210945.25863-1-dariobin@libero.it
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/tty/serial/omap-serial.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index 76b94d0ff586..1583e93b2202 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -302,7 +302,8 @@ static void serial_omap_stop_tx(struct uart_port *port)
 			serial_out(up, UART_OMAP_SCR, up->scr);
 			res = (port->rs485.flags & SER_RS485_RTS_AFTER_SEND) ?
 				1 : 0;
-			if (gpiod_get_value(up->rts_gpiod) != res) {
+			if (up->rts_gpiod &&
+			    gpiod_get_value(up->rts_gpiod) != res) {
 				if (port->rs485.delay_rts_after_send > 0)
 					mdelay(
 					port->rs485.delay_rts_after_send);
@@ -411,7 +412,7 @@ static void serial_omap_start_tx(struct uart_port *port)
 
 		/* if rts not already enabled */
 		res = (port->rs485.flags & SER_RS485_RTS_ON_SEND) ? 1 : 0;
-		if (gpiod_get_value(up->rts_gpiod) != res) {
+		if (up->rts_gpiod && gpiod_get_value(up->rts_gpiod) != res) {
 			gpiod_set_value(up->rts_gpiod, res);
 			if (port->rs485.delay_rts_before_send > 0)
 				mdelay(port->rs485.delay_rts_before_send);
@@ -1407,18 +1408,13 @@ serial_omap_config_rs485(struct uart_port *port, struct serial_rs485 *rs485)
 	/* store new config */
 	port->rs485 = *rs485;
 
-	/*
-	 * Just as a precaution, only allow rs485
-	 * to be enabled if the gpio pin is valid
-	 */
 	if (up->rts_gpiod) {
 		/* enable / disable rts */
 		val = (port->rs485.flags & SER_RS485_ENABLED) ?
 			SER_RS485_RTS_AFTER_SEND : SER_RS485_RTS_ON_SEND;
 		val = (port->rs485.flags & val) ? 1 : 0;
 		gpiod_set_value(up->rts_gpiod, val);
-	} else
-		port->rs485.flags &= ~SER_RS485_ENABLED;
+	}
 
 	/* Enable interrupts */
 	up->ier = mode;
-- 
2.30.2