Re: [PATCH] PM: sleep: Allow disabling DPM watchdog by default

[Tzung-Bi Shih <tzungbi@kernel.org>]

On Mon, Jun 01, 2026 at 08:39:42PM +0200, Rafael J. Wysocki wrote:
> On Thu, May 28, 2026 at 12:32 PM Tzung-Bi Shih <tzungbi@kernel.org> wrote:
> > diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> > index e1b550664bab..4f92905f3edf 100644
> > --- a/drivers/base/power/main.c
> > +++ b/drivers/base/power/main.c
> > @@ -527,6 +527,20 @@ module_param(dpm_watchdog_all_cpu_backtrace, bool, 0644);
> >  MODULE_PARM_DESC(dpm_watchdog_all_cpu_backtrace,
> >                  "Backtrace all CPUs on DPM watchdog timeout");
> >
> > +#ifdef CONFIG_DPM_WATCHDOG_DEFAULT_ENABLED
> > +static unsigned int __read_mostly dpm_watchdog_enabled = 1;
> > +#else
> > +static unsigned int __read_mostly dpm_watchdog_enabled;
> > +#endif
> > +
> > +static int __init dpm_watchdog_setup(char *str)
> > +{
> > +       if (kstrtouint(str, 0, &dpm_watchdog_enabled) == 0)
> > +               return 1;
> > +       return 0;
> > +}
> > +__setup("dpm_watchdog_enabled=", dpm_watchdog_setup);
> 
> You might as well use a module parameter to allow this to be set or
> clear at run time.  Is there a particular reason why you only want it
> to be enabled or disabled via the kernel command line?

Thanks for the suggestion.  Mainly because in our use cases, we only need
to set it once at boot time.

Also, I was wondering if we need to consider potential races if the flag
can be set at runtime.  E.g.:
1) The flag is set.
2) dpm_watchdog_set() is called and the timer is started.
3) The flag is then unset.
4) The subsequent dpm_watchdog_clear() isn't stop the timer.

Given this, would you still suggest providing the module parameter for
completeness?

> 
> > +
> >  /**
> >   * dpm_watchdog_handler - Driver suspend / resume watchdog handler.
> >   * @t: The timer that PM watchdog depends on.
> > @@ -570,6 +584,9 @@ static void dpm_watchdog_set(struct dpm_watchdog *wd, struct device *dev)
> >  {
> >         struct timer_list *timer = &wd->timer;
> >
> > +       if (!dpm_watchdog_enabled)
> > +               return;
> > +
> >         wd->dev = dev;
> >         wd->tsk = current;
> >         wd->fatal = CONFIG_DPM_WATCHDOG_TIMEOUT == CONFIG_DPM_WATCHDOG_WARNING_TIMEOUT;
> > @@ -588,6 +605,9 @@ static void dpm_watchdog_clear(struct dpm_watchdog *wd)
> >  {
> >         struct timer_list *timer = &wd->timer;
> >
> > +       if (!dpm_watchdog_enabled)
> > +               return;
> > +
> >         timer_delete_sync(timer);
> >         timer_destroy_on_stack(timer);
> >  }