Re: [PATCH] cpuidle: dt: fix opencoded for_each_cpu() in idle_state_valid()

[Rafael J. Wysocki]

On Mon, Jul 7, 2025 at 5:31 PM Yury Norov <yury.norov@xxxxxxxxx> wrote:
>
> On Wed, Jul 02, 2025 at 08:27:21PM +0200, Rafael J. Wysocki wrote:
> > On Wed, Jun 4, 2025 at 11:39 PM Yury Norov <yury.norov@xxxxxxxxx> wrote:
> > >
> > > From: Yury Norov [NVIDIA] <yury.norov@xxxxxxxxx>
> > >
> > > The function opencodes the for_each_cpu_from() by using an open for-loop.
> > > Fix that in sake of readability.
> > >
> > > While there, drop the 'valid' variable as it's pretty useless here.
> > >
> > > Signed-off-by: Yury Norov [NVIDIA] <yury.norov@xxxxxxxxx>
> > > ---
> > >  drivers/cpuidle/dt_idle_states.c | 14 +++++---------
> > >  1 file changed, 5 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/drivers/cpuidle/dt_idle_states.c b/drivers/cpuidle/dt_idle_states.c
> > > index 97feb7d8fb23..558d49838990 100644
> > > --- a/drivers/cpuidle/dt_idle_states.c
> > > +++ b/drivers/cpuidle/dt_idle_states.c
> > > @@ -98,7 +98,6 @@ static bool idle_state_valid(struct device_node *state_node, unsigned int idx,
> > >  {
> > >         int cpu;
> > >         struct device_node *cpu_node, *curr_state_node;
> > > -       bool valid = true;
> > >
> > >         /*
> > >          * Compare idle state phandles for index idx on all CPUs in the
> > > @@ -107,20 +106,17 @@ static bool idle_state_valid(struct device_node *state_node, unsigned int idx,
> > >          * retrieved from. If a mismatch is found bail out straight
> > >          * away since we certainly hit a firmware misconfiguration.
> > >          */
> > > -       for (cpu = cpumask_next(cpumask_first(cpumask), cpumask);
> > > -            cpu < nr_cpu_ids; cpu = cpumask_next(cpu, cpumask)) {
> > > +       cpu = cpumask_first(cpumask) + 1;
> >
> > Doing
> >
> > cpu = cpumask_next(cpumask_first(cpumask), cpumask);
> >
> > here might save a few iterations for sparse cpumasks.
>
> For that it's better to use cpumask_nth(1).
>
> I believe there will be no benefit in calling cpumask_next() before
> entering the loop because for_each_cpu_from() is based on it, and it
> will be called anyways.

Fair enough.