linux-kernel - Re: [PATCH 1/2] watchdog: introduce watchdog_dev

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Date:   Wed, 16 Jun 2021 10:57:35 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Grzegorz Jaszczyk <grzegorz.jaszczyk@...aro.org>
Cc:     wim@...ux-watchdog.org, shawnguo@...nel.org,
        linux-watchdog@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] watchdog: introduce watchdog_dev_suspend/resume

On Wed, Jun 16, 2021 at 03:59:23PM +0200, Grzegorz Jaszczyk wrote:
> On Tue, 15 Jun 2021 at 16:18, Guenter Roeck <linux@...ck-us.net> wrote:
> >
> > On Tue, Jun 15, 2021 at 02:39:03PM +0200, Grzegorz Jaszczyk wrote:
> > > The watchdog drivers often disable wdog clock during suspend and then
> > > enable it again during resume. Nevertheless the ping worker is still
> > > running and can issue low-level ping while the wdog clock is disabled
> > > causing the system hang. To prevent such condition introduce
> > > watchdog_dev_suspend/resume which can be used by any wdog driver and
> > > actually cancel ping worker during suspend and restore it back, if
> > > needed, during resume.
> > >
> >
> > I'll have to look into this further, but I don't think this is the correct
> > solution. Most likely the watchdog core needs to have its own independent
> > suspend/resule functions and suspend the high resolution timer on
> > suspend and restore it on resume. This may require an additional flag
> > to be set by drivers to indicate that the timer should be stopped on
> > suspend.
> 
> That makes sense - thank you for your suggestion. I think I could
> register a pm notifier in the watchdog core when the new e.g.
> WDOG_STOP_PING_ON_SUSPEND status flag will be set by the driver and
> actually call watchdog_dev_suspend/resume from the notifier callback.
> Please let me know if you see any other issue with this solution, if
> not I will post v2.
> 
Go for it.

Thanks,
Guenter