Re: [PATCH] watchdog: qcom: Move suspend/resume to suspend_late/resume_early

[Sai Prakash Ranjan]

Hi Guenter,

On 2021-03-11 01:53, Guenter Roeck wrote:
> On Thu, Mar 11, 2021 at 01:50:04AM +0530, Sai Prakash Ranjan wrote:
> > During suspend/resume usecases and tests, it is common to see issues
> > such as lockups either in suspend path or resume path because of the
> > bugs in the corresponding device driver pm handling code. In such 
> > cases,
> > it is important that watchdog is active to make sure that we either
> > receive a watchdog pretimeout notification or a bite causing reset
> > instead of a hang causing us to hard reset the machine.
> >
> > There are good reasons as to why we need this because:
> >
> > * We can have a watchdog pretimeout governor set to panic in which
> >   case we can have a backtrace which would help identify the issue
> >   with the particular driver and cause a normal reboot.
> >
> > * Even in case where there is no pretimeout support, a watchdog
> >   bite is still useful because some firmware has debug support to dump
> >   CPU core context on watchdog bite for post-mortem analysis.
> >
> > * One more usecase which comes to mind is of warm reboot. In case we
> >   hard reset the target, a cold reboot could be induced resulting in
> >   lose of ddr contents thereby losing all the debug info.
> >
> > Currently, the watchdog pm callback just invokes the usual suspend
> > and resume callback which do not have any special ordering in the
> > sense that a watchdog can be suspended before the buggy device driver
> > suspend callback and watchdog resume can happen after the buggy device
> > driver resume callback. This would mean that the watchdog will not be
> > active when the buggy driver cause the lockups thereby hanging the
> > system. So to make sure this doesn't happen, move the watchdog pm to
> > use late/early system pm callbacks which will ensure that the watchdog
> > is suspended late and resumed early so that it can catch such issues.
> >
> > Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
>
> Reviewed-by: Guenter Roeck <linux@xxxxxxxxxxxx>

Gentle Ping. I don't see this in linux-next or linux-watchdog, please 
let
me know if anything is pending from my side.

Thanks,
Sai

> > ---
> >  drivers/watchdog/qcom-wdt.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/watchdog/qcom-wdt.c b/drivers/watchdog/qcom-wdt.c
> > index e38a87ffe5f5..0d2209c5eaca 100644
> > --- a/drivers/watchdog/qcom-wdt.c
> > +++ b/drivers/watchdog/qcom-wdt.c
> > @@ -329,7 +329,9 @@ static int __maybe_unused qcom_wdt_resume(struct 
> > device *dev)
> >  	return 0;
> >  }
> >
> > -static SIMPLE_DEV_PM_OPS(qcom_wdt_pm_ops, qcom_wdt_suspend, 
> > qcom_wdt_resume);
> > +static const struct dev_pm_ops qcom_wdt_pm_ops = {
> > +	SET_LATE_SYSTEM_SLEEP_PM_OPS(qcom_wdt_suspend, qcom_wdt_resume)
> > +};
> >
> >  static const struct of_device_id qcom_wdt_of_table[] = {
> >  	{ .compatible = "qcom,kpss-timer", .data = &match_data_apcs_tmr },
> > --
> > QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a 
> > member
> > of Code Aurora Forum, hosted by The Linux Foundation

--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a 
member
of Code Aurora Forum, hosted by The Linux Foundation