Re: [V4] serial: core: Do stop_rx in suspend path for console if console_suspend is disabled

[Vijaya Krishna Nivarthi <quic_vnivarth@quicinc.com>]

Hi,

On 5/24/2022 5:24 PM, Marek Szyprowski wrote:
> 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@quicinc.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.
>
Ideally, as comments indicate, the set_termios should have done stop_rx 
at begin and start_rx at end to take care of this issue.

This is probably missing in your driver. Can we check if this can be 
fixed? OR other option is

Add a start_rx in uart_resume_port after call to set_termios to handle 
this scenario for other drivers.

Please let me know if there are any concerns for this options.

>>>    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
Thank you.