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

From: Vijaya Krishna Nivarthi <quic_vnivarth@quicinc.com>
To: Marek Szyprowski <m.szyprowski@samsung.com>,
	<gregkh@linuxfoundation.org>, <jirislaby@kernel.org>,
	<linux-serial@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Cc: <quic_msavaliy@quicinc.com>, <dianders@chromium.org>,
	<mka@chromium.org>, <swboyd@chromium.org>
Subject: Re: [V4] serial: core: Do stop_rx in suspend path for console if console_suspend is disabled
Date: Thu, 2 Jun 2022 21:12:31 +0530	[thread overview]
Message-ID: <cb802fb1-d0b8-68af-1c04-f73bc1beca77@quicinc.com> (raw)
In-Reply-To: <fb44af37-daf7-974d-95fe-1a6c2cdab676@samsung.com>

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@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?
> 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.
>>
>> 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