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

[Vijaya Krishna Nivarthi]

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@xxxxxxxxxxx>
> > > > > > ---
> > > > > > 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