linux-kernel - Re: [PATCH v2] cpuidle: Fail cpuidle device registration if there is one already

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Message-ID: <CAJZ5v0himPgJrg7s0G7HbgFTtawEMRCJBXiuvaZnT1z9MB_mqw@mail.gmail.com>
Date: Fri, 19 Sep 2025 14:40:11 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Dhruva Gole <d-gole@...com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Linux PM <linux-pm@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>, Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH v2] cpuidle: Fail cpuidle device registration if there is
 one already

On Fri, Sep 19, 2025 at 1:39 PM Dhruva Gole <d-gole@...com> wrote:
>
> Hi Rafael,
>
> On Sep 19, 2025 at 13:22:20 +0200, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >
> > Refuse to register a cpuidle device if the given CPU has a cpuidle
> > device already and print a message regarding it.
> >
> > Without this, an attempt to register a new cpuidle device without
> > unregistering the existing one leads to the removal of the existing
> > cpuidle device without removing its sysfs interface.
> >
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > ---
> >
> > v1 -> v2:
> >    * Add the new check before the driver module reference counting (Dhruva).
>
> Thanks for addressing!
>
> >
> > ---
> >  drivers/cpuidle/cpuidle.c |    8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > --- a/drivers/cpuidle/cpuidle.c
> > +++ b/drivers/cpuidle/cpuidle.c
> > @@ -635,8 +635,14 @@ static void __cpuidle_device_init(struct
> >  static int __cpuidle_register_device(struct cpuidle_device *dev)
> >  {
> >       struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
> > +     unsigned int cpu = dev->cpu;
> >       int i, ret;
> >
> > +     if (per_cpu(cpuidle_devices, cpu)) {
> > +             pr_info("CPU%d: cpuidle device already registered\n", cpu);
>
> Sorry for not pointing this earlier,
> perhaps pr_err makes more sense?

No, this need not mean a functional issue.