linux-kernel - Re: [PATCH v2 2/2] cpuidle: Change :enter_dead() driver callback return type to void

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Message-ID: <CAJZ5v0i48ph7Qa9ZRwJu6EEh_1Rs9xmsHw9KqdO6zH6RyJFrsg@mail.gmail.com>
Date: Tue, 19 Nov 2024 18:13:31 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: "Gautham R. Shenoy" <gautham.shenoy@....com>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>, Linux PM <linux-pm@...r.kernel.org>, 
	Peter Zijlstra <peterz@...radead.org>, LKML <linux-kernel@...r.kernel.org>, 
	x86 Maintainers <x86@...nel.org>, Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>, 
	Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>, 
	Mario Limonciello <mario.limonciello@....com>, Linux ACPI <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] cpuidle: Change :enter_dead() driver callback
 return type to void

Hi Gautham,

On Tue, Nov 19, 2024 at 4:09 PM Gautham R. Shenoy
<gautham.shenoy@....com> wrote:
>
> Hello Rafael,
>
> On Fri, Nov 15, 2024 at 10:00:25PM +0100, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >
> > After a previous change, cpuidle_play_dead(), which is the only caller
> > of idle state :enter_dead() callbacks, ignores their return values, so
> > they may as well be void.
> >
> > Suggested-by: Peter Zijlstra <peterz@...radead.org>
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> > ---
> >
> > v1 -> v2: New patch
> >
> > Interestingly enough, the only user of :enter_dead() idle state callbacks
> > in the current mainline turns out to be ACPI idle.
>
> For that matter, the only user of cpuidle_play_dead() is the
> native_play_dead(). Was that always the case?

At least as long ago as of 4.20.

> Some of the other architectures select the deepest available idle
> state at boot time, and enter that state when a CPU is offlined.

That's fine as long as the state to use is already known at that time.

> In any case I am ok with this.
>
> Reviewed-by: Gautham R. Shenoy <gautham.shenoy@....com>
> --
> Thanks and Regards
> gautham.
> >
> > ---
> >  drivers/acpi/processor_idle.c |    7 ++-----
> >  include/linux/cpuidle.h       |    2 +-
> >  2 files changed, 3 insertions(+), 6 deletions(-)
> >
> > Index: linux-pm/include/linux/cpuidle.h
> > ===================================================================
> > --- linux-pm.orig/include/linux/cpuidle.h
> > +++ linux-pm/include/linux/cpuidle.h
> > @@ -61,7 +61,7 @@ struct cpuidle_state {
> >                       struct cpuidle_driver *drv,
> >                       int index);
> >
> > -     int (*enter_dead) (struct cpuidle_device *dev, int index);
> > +     void (*enter_dead) (struct cpuidle_device *dev, int index);
> >
> >       /*
> >        * CPUs execute ->enter_s2idle with the local tick or entire timekeeping
> > Index: linux-pm/drivers/acpi/processor_idle.c
> > ===================================================================
> > --- linux-pm.orig/drivers/acpi/processor_idle.c
> > +++ linux-pm/drivers/acpi/processor_idle.c
> > @@ -578,7 +578,7 @@ static void __cpuidle acpi_idle_do_entry
> >   * @dev: the target CPU
> >   * @index: the index of suggested state
> >   */
> > -static int acpi_idle_play_dead(struct cpuidle_device *dev, int index)
> > +static void acpi_idle_play_dead(struct cpuidle_device *dev, int index)
> >  {
> >       struct acpi_processor_cx *cx = per_cpu(acpi_cstate[index], dev->cpu);
> >
> > @@ -591,11 +591,8 @@ static int acpi_idle_play_dead(struct cp
> >               else if (cx->entry_method == ACPI_CSTATE_SYSTEMIO) {
> >                       io_idle(cx->address);
> >               } else
> > -                     return -ENODEV;
> > +                     return;
> >       }
> > -
> > -     /* Never reached */
> > -     return 0;
> >  }
> >
> >  static __always_inline bool acpi_idle_fallback_to_c1(struct acpi_processor *pr)
> >
> >
> >
>