linux-kernel - Re: [V2] drivers/tty/serial/qcom-geni-serial: Do stop_rx in suspend path for console if console

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Date:   Wed, 6 Apr 2022 10:29:39 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
Cc:     agross@...nel.org, bjorn.andersson@...aro.org,
        gregkh@...uxfoundation.org, jirislaby@...nel.org,
        linux-arm-msm@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org, quic_msavaliy@...cinc.com,
        dianders@...omium.org
Subject: Re: [V2] drivers/tty/serial/qcom-geni-serial: Do stop_rx in suspend
 path for console if console_suspend is disabled

On Wed, Apr 06, 2022 at 01:56:52PM +0530, Vijaya Krishna Nivarthi wrote:
> For the case of console_suspend disabled, if back to back suspend/resume
> test is executed, at the end of test, sometimes console would appear to
> be frozen not responding to input. This would happen because, for
> console_suspend disabled, suspend/resume routines only turn resources
> off/on but don't do a port close/open.
> As a result, during resume, some rx transactions come in before system is
> ready, malfunction of rx happens in turn resulting in console appearing
> to be stuck.
> 
> Do a stop_rx in suspend sequence to prevent this. start_rx is already
> present in resume sequence as part of call to set_termios which does a
> stop_rx/start_rx.
> 
> Signed-off-by: Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
> ---
>  drivers/tty/serial/qcom_geni_serial.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
> index 1543a60..6f767c7 100644
> --- a/drivers/tty/serial/qcom_geni_serial.c
> +++ b/drivers/tty/serial/qcom_geni_serial.c
> @@ -1481,6 +1481,10 @@ static int __maybe_unused qcom_geni_serial_sys_suspend(struct device *dev)
>  	struct uart_port *uport = &port->uport;
>  	struct qcom_geni_private_data *private_data = uport->private_data;
>  
> +	/* do a stop_rx here, start_rx is handled in uart_resume_port by call to setermios */
> +	if (!console_suspend_enabled && uart_console(uport))

nit: I think for a human reader would be slightly clearer to swap the order
of the conditions, i.e.:

	if (uart_console(uport) && !console_suspend_enabled)

> +		uport->ops->stop_rx(uport);
> +
>  	/*
>  	 * This is done so we can hit the lowest possible state in suspend
>  	 * even with no_console_suspend

v1 one had additional changes which weren't directly related with
console_suspend. They looked worthwhile though, please make sure to
send them in separate patches.