linux-kernel - [PATCH 5.15 046/171] serial: pl011: Fix incorrect rs485 RTS polarity on set

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Date:   Mon, 31 Jan 2022 11:55:11 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Lino Sanfilippo <LinoSanfilippo@....de>,
        Jochen Mades <jochen@...es.net>, Lukas Wunner <lukas@...ner.de>
Subject: [PATCH 5.15 046/171] serial: pl011: Fix incorrect rs485 RTS polarity on set_mctrl

From: Jochen Mades <jochen@...es.net>

commit 62f676ff7898f6c1bd26ce014564773a3dc00601 upstream.

Commit 8d479237727c ("serial: amba-pl011: add RS485 support") sought to
keep RTS deasserted on set_mctrl if rs485 is enabled.  However it did so
only if deasserted RTS polarity is high.  Fix it in case it's low.

Fixes: 8d479237727c ("serial: amba-pl011: add RS485 support")
Cc: stable@...r.kernel.org # v5.15+
Cc: Lino Sanfilippo <LinoSanfilippo@....de>
Signed-off-by: Jochen Mades <jochen@...es.net>
[lukas: copyedit commit message, add stable designation]
Signed-off-by: Lukas Wunner <lukas@...ner.de>
Link: https://lore.kernel.org/r/85fa3323ba8c307943969b7343e23f34c3e652ba.1642909284.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/tty/serial/amba-pl011.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1615,8 +1615,12 @@ static void pl011_set_mctrl(struct uart_
 	    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);