Re: [PATCH v1] cpuidle: Do not return from cpuidle_play_dead() on callback failures

[Rafael J. Wysocki]

On Fri, Nov 15, 2024 at 11:14 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Thu, Nov 14, 2024 at 06:46:20PM +0100, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> >
> > If the :enter_dead() idle state callback fails for a certain state,
> > there may be still a shallower state for which it will work.
> >
> > Because the only caller of cpuidle_play_dead(), native_play_dead(),
> > falls back to hlt_play_dead() if it returns an error, it should
> > better try all of the idle states for which :enter_dead() is present
> > before failing, so change it accordingly.
> >
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > ---
> >  drivers/cpuidle/cpuidle.c |    7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > Index: linux-pm/drivers/cpuidle/cpuidle.c
> > ===================================================================
> > --- linux-pm.orig/drivers/cpuidle/cpuidle.c
> > +++ linux-pm/drivers/cpuidle/cpuidle.c
> > @@ -70,9 +70,10 @@ int cpuidle_play_dead(void)
> >               return -ENODEV;
> >
> >       /* Find lowest-power state that supports long-term idle */
> > -     for (i = drv->state_count - 1; i >= 0; i--)
> > -             if (drv->states[i].enter_dead)
> > -                     return drv->states[i].enter_dead(dev, i);
> > +     for (i = drv->state_count - 1; i >= 0; i--) {
> > +             if (drv->states[i].enter_dead && !drv->states[i].enter_dead(dev, i))
> > +                     return 0;
> > +     }
>
> Hmm, strictly speaking there is no 'success' return from play_dead(). On
> success, the CPU is dead :-)

Well, would you prefer something like

for (i = drv->state_count - 1; i >= 0; i--) {
        if (drv->states[i].enter_dead)
                drv->states[i].enter_dead(dev, i);
}

and adding a comment before the final return statement that
:enter_dead() only returns on failure?