Re: [PATCH 3/4] ACPI: processor idle: Only flush cache on entering C3

[Kirill A. Shutemov]

On Wed, Dec 08, 2021 at 05:26:12PM +0100, Rafael J. Wysocki wrote:
> On Mon, Dec 6, 2021 at 4:03 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> >
> > On Mon, Dec 06, 2021 at 03:29:51PM +0300, Kirill A. Shutemov wrote:
> > > According to the ACPI spec v6.4, section 8.2, cache flushing required
> > > on entering C3 power state.
> > >
> > > Avoid flushing cache on entering other power states.
> > >
> > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > > ---
> > >  drivers/acpi/processor_idle.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> > > index 76ef1bcc8848..01495aca850e 100644
> > > --- a/drivers/acpi/processor_idle.c
> > > +++ b/drivers/acpi/processor_idle.c
> > > @@ -567,7 +567,8 @@ static int acpi_idle_play_dead(struct cpuidle_device *dev, int index)
> > >  {
> > >       struct acpi_processor_cx *cx = per_cpu(acpi_cstate[index], dev->cpu);
> > >
> > > -     ACPI_FLUSH_CPU_CACHE();
> > > +     if (cx->type == ACPI_STATE_C3)
> > > +             ACPI_FLUSH_CPU_CACHE();
> > >
> >
> > acpi_idle_enter() already does this, acpi_idle_enter_s2idle() has it
> > confused again,
> 
> No, they do the same thing: acpi_idle_enter_bm() if flags.bm_check is set.
> 
> > Also, I think acpi_idle_enter() does it too late; consider
> > acpi_idle_enter_mb(). Either that or the BM crud needs more comments.
> 
> I think the latter.
> 
> Evidently, acpi_idle_play_dead(() doesn't support FFH and the BM
> thing, so it is only necessary to flush the cache when using
> ACPI_CSTATE_SYSTEMIO and when cx->type is C3.

I'm new to this and not completely follow what I need to change.

Does it look correct?