linux-kernel - [PATCH AUTOSEL 5.5 081/121] tty: serial: qcom_geni_serial: No need to stop tx/rx on UART shutdown

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Date:   Sat, 11 Apr 2020 19:06:26 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Douglas Anderson <dianders@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sasha Levin <sashal@...nel.org>, linux-arm-msm@...r.kernel.org,
        linux-serial@...r.kernel.org
Subject: [PATCH AUTOSEL 5.5 081/121] tty: serial: qcom_geni_serial: No need to stop tx/rx on UART shutdown

From: Douglas Anderson <dianders@...omium.org>

[ Upstream commit e83766334f96b3396a71c7baa3b0b53dfd5190cd ]

On a board using qcom_geni_serial I found that I could no longer
interact with kdb if I got a crash after the "agetty" running on the
same serial port was killed.  This meant that various classes of
crashes that happened at reboot time were undebuggable.

Reading through the code, I couldn't figure out why qcom_geni_serial
felt the need to run so much code at port shutdown time.  All we need
to do is disable the interrupt.

After I make this change then a hardcoded kgdb_breakpoint in some late
shutdown code now allows me to interact with the debugger.  I also
could freely close / re-open the port without problems.

Fixes: c4f528795d1a ("tty: serial: msm_geni_serial: Add serial driver support for GENI based QUP")
Signed-off-by: Douglas Anderson <dianders@...omium.org>
Link: https://lore.kernel.org/r/20200313134635.1.Icf54c533065306b02b880c46dfd401d8db34e213@changeid
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/tty/serial/qcom_geni_serial.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
index ebace5ad175ca..7a6fa4ab780f7 100644
--- a/drivers/tty/serial/qcom_geni_serial.c
+++ b/drivers/tty/serial/qcom_geni_serial.c
@@ -846,17 +846,11 @@ static void get_tx_fifo_size(struct qcom_geni_serial_port *port)
 
 static void qcom_geni_serial_shutdown(struct uart_port *uport)
 {
-	unsigned long flags;
-
 	/* Stop the console before stopping the current tx */
 	if (uart_console(uport))
 		console_stop(uport->cons);
 
 	disable_irq(uport->irq);
-	spin_lock_irqsave(&uport->lock, flags);
-	qcom_geni_serial_stop_tx(uport);
-	qcom_geni_serial_stop_rx(uport);
-	spin_unlock_irqrestore(&uport->lock, flags);
 }
 
 static int qcom_geni_serial_port_setup(struct uart_port *uport)
-- 
2.20.1