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

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Message-ID: <f525c352-d995-0589-584f-0e9acf419f80@quicinc.com>
Date:   Sat, 4 Jun 2022 00:24:23 +0530
From:   Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
To:     Marek Szyprowski <m.szyprowski@...sung.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 6/2/2022 9:12 PM, Vijaya Krishna Nivarthi wrote:
> Hi,
>
>
> On 6/2/2022 3:55 AM, Marek Szyprowski wrote:
>> Hi,
>>
>> On 01.06.2022 13:24, Vijaya Krishna Nivarthi wrote:
>>> 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@...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.
>>>>
>>> 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?
>> Sure, just point me what need to be added in amba-pl011.c and
>> samsung_tty.c. I've briefly compared the suspend/resume paths of those
>> drivers with other drivers and I don't see anything missing there.
>>
>>> OR other option is
>>>
>>> Add a start_rx in uart_resume_port after call to set_termios to handle
>>> this scenario for other drivers.

Since start_rx is not exposed it doesn't seem like we will be able to 
handle it in core.

In your drivers, Can we add a call to stop_rx at begin of set_termios 
and then undo it at end?

That would ensure that set_termios functionality is unaffected while 
fixing the broken cases?

If that's not an option we will have to go back to a previous version of 
limiting the change to qcom driver.

Thank you.

>>>
>>> Please let me know if there are any concerns for this options.
>> IMHO this looks like an issue that affects lots of drivers and it should
>> be handled in the core.
>
> Sure, we will look into both aspects and get back as soon as possible.
>
> Thank you.
>
>>
>>   > ...
>>
>> Best regards