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

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Date:   Tue, 24 May 2022 13:54:07 +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

On 23.05.2022 23:32, Marek Szyprowski wrote:
> 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.


One more information. This issue can be easily reproduced with QEMU. It 
happens both on ARM 32bit and ARM 64bit QEMU's 'virt' machines when 
'no_console_suspend' is added to kernel's cmdline.


>
>>   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

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