linux-kernel - Re: [PATCH 1/3] tty: serial: qcom-geni-serial: Fix kdb/kgdb after port shutdown (again)

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Date:   Tue, 7 Mar 2023 16:46:03 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Bjorn Andersson <andersson@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        linux-serial@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        kgdb-bugreport@...ts.sourceforge.net,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Andy Gross <agross@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] tty: serial: qcom-geni-serial: Fix kdb/kgdb after
 port shutdown (again)

On Tue, Mar 7, 2023 at 4:33 PM Douglas Anderson <dianders@...omium.org> wrote:
>
> Commit d8aca2f96813 ("tty: serial: qcom-geni-serial: stop operations
> in progress at shutdown") was basically a straight revert of the
> commit it claims to fix without any explanation of why the problems
> talked about in the original patch were no longer relevant. Indeed,
> commit d8aca2f96813 ("tty: serial: qcom-geni-serial: stop operations
> in progress at shutdown") re-introduces the same problem that commit
> e83766334f96 ("tty: serial: qcom_geni_serial: No need to stop tx/rx on
> UART shutdown") fixed.
>
> The problems are very easy to see by simply doing this on a
> sc7180-based Chromebook:
>
> 1. Boot in developer mode with serial console enabled and kdb setup on
>    the serial console.
> 2. via ssh: stop console-ttyMSM0; echo g > /proc/sysrq-trigger
>
> When you do the above you'll see the "kdb" prompt printed on the
> serial console but be unable to interact with it.
>
> Let's fix the problem again by noting that the console port is never
> configured in DMA mode and thus we don't need to stop things for the
> console.
>
> Fixes: d8aca2f96813 ("tty: serial: qcom-geni-serial: stop operations in progress at shutdown")
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
>
>  drivers/tty/serial/qcom_geni_serial.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
> index d69592e5e2ec..74a0e074c2de 100644
> --- a/drivers/tty/serial/qcom_geni_serial.c
> +++ b/drivers/tty/serial/qcom_geni_serial.c
> @@ -1070,8 +1070,10 @@ static int setup_fifos(struct qcom_geni_serial_port *port)
>  static void qcom_geni_serial_shutdown(struct uart_port *uport)
>  {
>         disable_irq(uport->irq);
> -       qcom_geni_serial_stop_tx(uport);
> -       qcom_geni_serial_stop_rx(uport);
> +       if (!uart_console(uport)) {
> +               qcom_geni_serial_stop_tx(uport);
> +               qcom_geni_serial_stop_rx(uport);
> +       }
>  }
>
>  static int qcom_geni_serial_port_setup(struct uart_port *uport)
> --
> 2.40.0.rc0.216.gc4246ad0f0-goog
>

And also:

Tested-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>