linux-kernel - Re: [PATCH v1 02/10] cpufreq: Add a flag to auto-register a cooling device

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Message-ID: <CAHLCerPFcxX1LeeY0kRp5_4ayKtzzWkQUv6p8pjJ1ELxKt1LhA@mail.gmail.com>
Date:   Mon, 21 Jan 2019 19:53:12 +0530
From:   Amit Kucheria <amit.kucheria@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Eduardo Valentin <edubezval@...il.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Douglas Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v1 02/10] cpufreq: Add a flag to auto-register a cooling device

On Thu, Jan 17, 2019 at 10:12 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 17-01-19, 00:03, Rafael J. Wysocki wrote:
> > On Monday, January 14, 2019 5:34:54 PM CET Amit Kucheria wrote:
> > > All cpufreq drivers do similar things to register as a cooling device.
> > > Provide a cpufreq driver flag so drivers can just ask the cpufreq core
> > > to register the cooling device on their behalf. This allows us to get
> > > rid of duplicated code in the drivers.
> > >
> > > Suggested-by: Stephen Boyd <swboyd@...omium.org>
> > > Suggested-by: Viresh Kumar <viresh.kumar@...aro.org>
> > > Signed-off-by: Amit Kucheria <amit.kucheria@...aro.org>
> > > ---
> > >  drivers/cpufreq/cpufreq.c | 17 +++++++++++++++++
> > >  include/linux/cpufreq.h   |  6 ++++++
> > >  2 files changed, 23 insertions(+)
> > >
> > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > > index 6f23ebb395f1..cd6e750d3d82 100644
> > > --- a/drivers/cpufreq/cpufreq.c
> > > +++ b/drivers/cpufreq/cpufreq.c
> > > @@ -30,6 +30,7 @@
> > >  #include <linux/syscore_ops.h>
> > >  #include <linux/tick.h>
> > >  #include <trace/events/power.h>
> > > +#include <linux/cpu_cooling.h>
> > >
> > >  static LIST_HEAD(cpufreq_policy_list);
> > >
> > > @@ -1318,6 +1319,14 @@ static int cpufreq_online(unsigned int cpu)
> > >     if (cpufreq_driver->ready)
> > >             cpufreq_driver->ready(policy);
> > >
> > > +#ifdef CONFIG_CPU_THERMAL
> > > +   if (cpufreq_driver->flags & CPUFREQ_AUTO_REGISTER_COOLING_DEV) {
> > > +           struct thermal_cooling_device **cdev = &policy->cooldev;
>
> We use cdev for the cooling device everywhere in the kernel, so please
> do s/cooldev/cdev/ in your patches.

Fixed

> > > +
> > > +           *cdev = of_cpufreq_cooling_register(policy);
> >
> > What would be wrong with
> >
> >               policy->cooldev = of_cpufreq_cooling_register(policy);
> >
> > > +   }
> > > +#endif
> >
> > Please remove the #ifdefs from cpufreq_online() and cpufreq_offline().
> >
> > Use wrappers that would become empty stubs for CONFIG_CPU_THERMAL unset.
> >
> > > +
> > >     pr_debug("initialization complete\n");
> > >
> > >     return 0;
> > > @@ -1411,6 +1420,14 @@ static int cpufreq_offline(unsigned int cpu)
> > >     if (has_target())
> > >             cpufreq_exit_governor(policy);
> > >
> > > +#ifdef CONFIG_CPU_THERMAL
> > > +   if (cpufreq_driver->flags & CPUFREQ_AUTO_REGISTER_COOLING_DEV) {
> > > +           struct thermal_cooling_device **cdev = &policy->cooldev;
> > > +
> > > +           cpufreq_cooling_unregister(*cdev);
> >
> > Again, why don't you simply pass policy->cooldev here?
>
> I also had the same comments when I looked at your patch :)
>
> I also think we must do the unregistering before calling stop_cpu()
> callback.

Fixed.

> > Also, would it make sense to clear policy->cooldev at this point?  It points
> > to freed memory after cpufreq_cooling_unregister().
>
> Since the core doesn't refer to this field at all and uses it only
> while registering/unregistering as a cooling device, there is no
> technical issue that we will have today. If someone uses the dangling
> pointer later on in future, it will be a bug. So I wouldn't care much
> about resetting it here.
>
> > > +   }
> > > +#endif
> > > +
> > >     /*
> > >      * Perform the ->exit() even during light-weight tear-down,
> > >      * since this is a core component, and is essential for the
> > > diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> > > index 7d0cf54125fa..70ad02088825 100644
> > > --- a/include/linux/cpufreq.h
> > > +++ b/include/linux/cpufreq.h
> > > @@ -390,6 +390,12 @@ struct cpufreq_driver {
> > >   */
> > >  #define CPUFREQ_NO_AUTO_DYNAMIC_SWITCHING (1 << 6)
> > >
> > > +/*
> > > + * Set by drivers that want the core to automatically register the cpufreq
> > > + * driver as a thermal cooling device
>
> Add a full-stop here please.

Fixed

Thanks for the review.


> > > + */
> > > +#define CPUFREQ_AUTO_REGISTER_COOLING_DEV (1 << 7)
> > > +
> > >  int cpufreq_register_driver(struct cpufreq_driver *driver_data);
> > >  int cpufreq_unregister_driver(struct cpufreq_driver *driver_data);
> > >