linux-kernel - [PATCH v2] tty/serial/imx: Enable TXEN bit in imx_poll

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Date:   Wed,  2 Dec 2020 15:25:43 +0800
From:   jiladahe1997 <jiladahe1997@...il.com>
To:     gregkh@...uxfoundation.org, shawnguo@...nel.org,
        s.hauer@...gutronix.de
Cc:     linux-imx@....com, linux-kernel@...r.kernel.org, 972931182@...com,
        Mingrui Ren <jiladahe1997@...il.com>
Subject: [PATCH v2] tty/serial/imx: Enable TXEN bit in imx_poll_init().

From: Mingrui Ren <jiladahe1997@...il.com>

As described in Documentation, poll_init() is called by kgdb to initialize
hardware which supports both poll_put_char() and poll_get_char().

It's necessary to enable TXEN bit, otherwise, it will cause hardware fault
and kernel panic when calling imx_poll_put_char().

Generally, if use /dev/ttymxc0 as kgdb console as well as system
console, ttymxc0 is initialized early by system console which does enable
TXEN bit.But when use /dev/ttymxc1 as kgbd console, ttymxc1 is only
initialized by imx_poll_init() cannot enable the TXEN bit, which will
cause kernel panic.

Signed-off-by: Mingrui Ren <jiladahe1997@...il.com>
---
Changes in v2:
 - Add ' ' around '|' for better code style.
 - Re-create patch on the latest master branch. 

 drivers/tty/serial/imx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index cacf7266a262..a66301b3b33d 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -1881,7 +1881,7 @@ static int imx_uart_poll_init(struct uart_port *port)
 	ucr1 |= UCR1_UARTEN;
 	ucr1 &= ~(UCR1_TRDYEN | UCR1_RTSDEN | UCR1_RRDYEN);

-	ucr2 |= UCR2_RXEN;
+	ucr2 |= UCR2_RXEN | UCR2_TXEN;
 	ucr2 &= ~UCR2_ATEN;

 	imx_uart_writel(sport, ucr1, UCR1);
-- 
2.28.0