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

[Vijaya Krishna Nivarthi]

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@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? 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.