Re: [PATCH] cpuidle: riscv-sbi: Add cluster_pm_enter()/exit()

[Nick Hu]

On Tue, Apr 30, 2024 at 12:22 AM Nick Hu <nick.hu@xxxxxxxxxx> wrote:
>
> Hi Ulf
>
> On Mon, Apr 29, 2024 at 10:32 PM Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
> >
> > On Mon, 26 Feb 2024 at 07:51, Nick Hu <nick.hu@xxxxxxxxxx> wrote:
> > >
> > > When the cpus in the same cluster are all in the idle state, the kernel
> > > might put the cluster into a deeper low power state. Call the
> > > cluster_pm_enter() before entering the low power state and call the
> > > cluster_pm_exit() after the cluster woken up.
> > >
> > > Signed-off-by: Nick Hu <nick.hu@xxxxxxxxxx>
> >
> > I was not cced this patch, but noticed that this patch got queued up
> > recently. Sorry for not noticing earlier.
> >
> > If not too late, can you please drop/revert it? We should really move
> > away from the CPU cluster notifiers. See more information below.
> >
> > > ---
> > >  drivers/cpuidle/cpuidle-riscv-sbi.c | 24 ++++++++++++++++++++++--
> > >  1 file changed, 22 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/cpuidle/cpuidle-riscv-sbi.c b/drivers/cpuidle/cpuidle-riscv-sbi.c
> > > index e8094fc92491..298dc76a00cf 100644
> > > --- a/drivers/cpuidle/cpuidle-riscv-sbi.c
> > > +++ b/drivers/cpuidle/cpuidle-riscv-sbi.c
> > > @@ -394,6 +394,7 @@ static int sbi_cpuidle_pd_power_off(struct generic_pm_domain *pd)
> > >  {
> > >         struct genpd_power_state *state = &pd->states[pd->state_idx];
> > >         u32 *pd_state;
> > > +       int ret;
> > >
> > >         if (!state->data)
> > >                 return 0;
> > > @@ -401,6 +402,10 @@ static int sbi_cpuidle_pd_power_off(struct generic_pm_domain *pd)
> > >         if (!sbi_cpuidle_pd_allow_domain_state)
> > >                 return -EBUSY;
> > >
> > > +       ret = cpu_cluster_pm_enter();
> > > +       if (ret)
> > > +               return ret;
> >
> > Rather than using the CPU cluster notifiers, consumers of the genpd
> > can register themselves to receive genpd on/off notifiers.
> >
> > In other words, none of this should be needed, right?
> >
> Thanks for the feedback!
> Maybe I miss something, I'm wondering about a case like below:
> If we have a shared L2 cache controller inside the cpu cluster power
> domain and we add this controller to be a consumer of the power
> domain, Shouldn't the genpd invoke the domain idle only after the
> shared L2 cache controller is suspended?
> Is there a way that we can put the L2 cache down while all cpus in the
> same cluster are idle?
> > [...]
Sorry, I made some mistake in my second question.
Update the question here:
Is there a way that we can save the L2 cache states while all cpus in the
same cluster are idle and the cluster could be powered down?
> >
> > Kind regards
> > Uffe