linux-kernel - Re: [V4] serial: core: Do stop_rx in suspend path for console if console

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Message-ID: <bf7eec57-6ad6-2c1a-ea61-0e1d06fc77f5@samsung.com>
Date:   Mon, 23 May 2022 23:32:46 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>,
        gregkh@...uxfoundation.org, jirislaby@...nel.org,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     quic_msavaliy@...cinc.com, dianders@...omium.org, mka@...omium.org,
        swboyd@...omium.org
Subject: Re: [V4] serial: core: Do stop_rx in suspend path for console if
 console_suspend is disabled

Hi,

On 16.05.2022 11:20, 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, during
> resume, rx transactions can 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.
>
> Signed-off-by: Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
> ---
> v4: moved the change to serial core to apply for all drivers
> v3: swapped the order of conditions to be more human readable
> v2: restricted patch to contain only stop_rx in suspend sequence
> v1: intial patch contained 2 additional unrelated changes in vicinity
> ---

This patch landed recently in linux-next as commit c9d2325cdb92 
("serial: core: Do stop_rx in suspend path for console if 
console_suspend is disabled").

Unfortunately it breaks console operation on my test systems after 
system suspend/resume cycle if 'no_console_suspend' kernel parameter is 
present. System properly resumes from suspend, the console displays all 
the messages and even command line prompt, but then doesn't react on any 
input. If I remove the 'no_console_suspend' parameter, the console is 
again operational after system suspend/resume cycle. Before this patch 
it worked fine regardless the 'no_console_suspend' parameter.

If this matters, the test system is ARM 32bit Samsung Exynos5422-based 
Odroid XU3lite board.

>   drivers/tty/serial/serial_core.c | 11 +++++++++--
>   1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 82a1770..9a85b41 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -2211,9 +2211,16 @@ int uart_suspend_port(struct uart_driver *drv, struct uart_port *uport)
>   	}
>   	put_device(tty_dev);
>   
> -	/* Nothing to do if the console is not suspending */
> -	if (!console_suspend_enabled && uart_console(uport))
> +	/*
> +	 * Nothing to do if the console is not suspending
> +	 * except stop_rx to prevent any asynchronous data
> +	 * over RX line. Re-start_rx, when required, is
> +	 * done by set_termios in resume sequence
> +	 */
> +	if (!console_suspend_enabled && uart_console(uport)) {
> +		uport->ops->stop_rx(uport);
>   		goto unlock;
> +	}
>   
>   	uport->suspended = 1;
>   

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland