[PATCH AUTOSEL 5.4 084/130] tty/serial/imx: Enable TXEN bit in imx_poll_init().

Sasha Levin sashal at kernel.org
Tue Dec 22 21:17:27 EST 2020

From: Mingrui Ren <jiladahe1997 at gmail.com>

[ Upstream commit aef1b6a27970607721a618a0b990716ca8dbbf97 ]

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 at gmail.com>
Link: https://lore.kernel.org/r/20201202072543.151-1-972931182@qq.com
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal at kernel.org>
 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 e5ed4ab2b08df..982953db58e95 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -1811,7 +1811,7 @@ static int imx_uart_poll_init(struct uart_port *port)
 	ucr1 |= UCR1_UARTEN;
-	ucr2 |= UCR2_RXEN;
+	ucr2 |= UCR2_RXEN | UCR2_TXEN;
 	ucr2 &= ~UCR2_ATEN;
 	imx_uart_writel(sport, ucr1, UCR1);

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