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

[Yury Norov <yury.norov@gmail.com>]

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@gmail.com> wrote:
> >
> > From: Yury Norov [NVIDIA] <yury.norov@gmail.com>
> >
> > 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@gmail.com>
> > ---
> >  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.

I can send v2 with cpumask_nth() change if you like it better. Please
let me know.

Thanks,
Yury
 
> > +       for_each_cpu_from(cpu, cpumask) {
> >                 cpu_node = of_cpu_device_node_get(cpu);
> >                 curr_state_node = of_get_cpu_state_node(cpu_node, idx);
> > -               if (state_node != curr_state_node)
> > -                       valid = false;
> > -
> >                 of_node_put(curr_state_node);
> >                 of_node_put(cpu_node);
> > -               if (!valid)
> > -                       break;
> > +               if (state_node != curr_state_node)
> > +                       return false;
> >         }
> >
> > -       return valid;
> > +       return true;
> >  }
> >
> >  /**
> > --
> > 2.43.0
> >