linux-kernel - Re: [PATCH] cpuidle: dt: fix opencoded for_each_cpu() in idle_state

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Message-ID: <CAJZ5v0iLewzEFBZPOc2bTRFjS7LZYdzPr7cmRnFt7h5p2gg4hg@mail.gmail.com>
Date: Thu, 10 Jul 2025 14:54:44 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Yury Norov <yury.norov@...il.com>
Cc: Daniel Lezcano <daniel.lezcano@...aro.org>, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpuidle: dt: fix opencoded for_each_cpu() in idle_state_valid()

On Mon, Jul 7, 2025 at 6:11 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Mon, Jul 7, 2025 at 5:31 PM Yury Norov <yury.norov@...il.com> 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@...il.com> wrote:
> > > >
> > > > From: Yury Norov [NVIDIA] <yury.norov@...il.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@...il.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.
>
> Fair enough.

And so applied as 6.17 material, thanks!