linux-kernel - [PATCH] serial: amba-pl011: fix high priority character transmission in rs486 mode

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Date:   Sun,  8 Jan 2023 19:17:35 +0100
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     gregkh@...uxfoundation.org, jirislaby@...nel.org
Cc:     linux@...linux.org.uk, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org, l.sanfilippo@...bus.com,
        LinoSanfilippo@....de, lukas@...ner.de, p.rosenberger@...bus.com,
        stable@...r.kernel.org
Subject: [PATCH] serial: amba-pl011: fix high priority character transmission in rs486 mode

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

In RS485 mode the transmission of a high priority character fails since it
is written to the data register before the transmitter is enabled. Fix this
in pl011_tx_chars() by enabling RS485 transmission before writing the
character.

Fixes: 8d479237727c ("serial: amba-pl011: add RS485 support")
Cc: stable@...r.kernel.org
Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
---
 drivers/tty/serial/amba-pl011.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index d75c39f4622b..d8c2f3455eeb 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1466,6 +1466,10 @@ static bool pl011_tx_chars(struct uart_amba_port *uap, bool from_irq)
 	struct circ_buf *xmit = &uap->port.state->xmit;
 	int count = uap->fifosize >> 1;
 
+	if ((uap->port.rs485.flags & SER_RS485_ENABLED) &&
+	    !uap->rs485_tx_started)
+		pl011_rs485_tx_start(uap);
+
 	if (uap->port.x_char) {
 		if (!pl011_tx_char(uap, uap->port.x_char, from_irq))
 			return true;
@@ -1477,10 +1481,6 @@ static bool pl011_tx_chars(struct uart_amba_port *uap, bool from_irq)
 		return false;
 	}
 
-	if ((uap->port.rs485.flags & SER_RS485_ENABLED) &&
-	    !uap->rs485_tx_started)
-		pl011_rs485_tx_start(uap);
-
 	/* If we are using DMA mode, try to send some characters. */
 	if (pl011_dma_tx_irq(uap))
 		return true;

base-commit: 93928d485d9df12be724cbdf1caa7d197b65001e
-- 
2.39.0