linux-kernel - [PATCH] Bugfix RTS line config in RS485 mode is overwritten in pl011_set

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Date:   Fri, 31 Dec 2021 17:15:14 +0000
From:   jmades <jochen@...es.net>
To:     gregkh@...uxfoundation.org
Cc:     jochen@...es.net, Russell King <linux@...linux.org.uk>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] Bugfix RTS line config in RS485 mode is overwritten in pl011_set_mctrl() function.

Based on the "0001-serial-amba-pl011-add-RS485-support.patch" this change is necesarry otherwise the RTS-line will be pulled up in SER_RS485_RTS_BEFORE_SEND mode before sending data. This hinders the driver to receive data, f.ex. when the device is an RS485 slave device.

Signed-off-by: jmades <jochen@...es.net>
---
 drivers/tty/serial/amba-pl011.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 537f37ac4..1749c1498 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1646,8 +1646,12 @@ static void pl011_set_mctrl(struct uart_port *port, unsigned int mctrl)
 	    container_of(port, struct uart_amba_port, port);
 	unsigned int cr;
 
-	if (port->rs485.flags & SER_RS485_ENABLED)
-		mctrl &= ~TIOCM_RTS;
+	if (port->rs485.flags & SER_RS485_ENABLED) {
+		if (port->rs485.flags & SER_RS485_RTS_AFTER_SEND)
+			mctrl &= ~TIOCM_RTS;
+		else
+			mctrl |= TIOCM_RTS;
+	}
 
 	cr = pl011_read(uap, REG_CR);
 
-- 
2.20.1