Re: [PATCH v1 1/4] ACPI: processor: Reorder acpi_processor_driver_init()

[Zhang, Rui]

On Mon, 2023-03-13 at 14:48 +0100, Rafael J. Wysocki wrote:
> On Sun, Mar 12, 2023 at 5:09 PM Zhang, Rui <rui.zhang@xxxxxxxxx>
> wrote:
> > On Fri, 2023-03-03 at 20:19 +0100, Rafael J. Wysocki wrote:
> > > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > > 
> > > The cpufreq policy notifier in the ACPI processor driver may as
> > > well be registered before the driver itself, which causes
> > > acpi_processor_cpufreq_init to be true (unless the notifier
> > > registration fails, which is unlikely at that point) when the
> > > ACPI CPU thermal cooling devices are registered, so the
> > > processor_get_max_state() result does not change while
> > > acpi_processor_driver_init() is running.
> > > 
> > > Change the ordering in acpi_processor_driver_init() accordingly
> > > to prevent the max_state value from remaining 0 permanently for
> > > all
> > > ACPI CPU cooling devices.
> > > 
> > > Fixes: a365105c685c("thermal: sysfs: Reuse cdev->max_state")
> > > Reported-by: Wang, Quanxian <quanxian.wang@xxxxxxxxx>
> > > Link:
> > > https://lore.kernel.org/linux-pm/53ec1f06f61c984100868926f282647e57ecfb2d.camel@xxxxxxxxx/
> > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > 
> > The full patch series fixes the problem but this one does not.
> 
> That is a correct observation, but the $subject patch fixes part of
> the problem (which is not addressed by the rest of the series AFAICS)
> and so it deserves a Fixes tag of its own IMO.

Am I understanding this correctly that this patch helps in below case?

cpufreq driver like intel_pstate is registered before we register the
notifier callback in processor_driver. In this case, we are not able to
catch the CPUFREQ_CREATE_POLICY notification and cpufreq should be
counted as part of cooling states when registering the ACPI CPU cooling
device. (acpi_processor_cpufreq_init must be set at this time)

Or else, in normal case, the ACPI CPU cdev->max_state always return 0
(when t-state not available) until we receive the CPUFREQ_CREATE_POLICY
notification and call thermal_cooling_device_update(), both with and
without this patch.

Patch 2,3,4 works on my test platform, without applying patch 1/4.

thanks,
rui

> 
> I guess I should clarify that in the changelog.
> 
> > This is because,
> > 
> > static int cpu_has_cpufreq(unsigned int cpu)
> > {
> >         struct
> > cpufreq_policy *policy;
> > 
> >         if (!acpi_processor_cpufreq_init)
> >                 return 0;
> > 
> >         policy = cpufreq_cpu_get(cpu);
> >         if (policy) {
> >                 cpufreq_cpu_put(policy);
> >                 return 1;
> >         }
> >         return 0;
> > }
> > 
> > Although acpi_processor_cpufreq_init is set to true with patch 1/4,
> > but
> > we don't have cpufreq driver registered, thus cpufreq_cpu_get()
> > return
> > NULL.
> > so acpi_processor_cpufreq_init is not the only dependency here. :(
> 
> Right.  That's why the other patches in the series are needed too.
> 
> > > ---
> > >  drivers/acpi/processor_driver.c |   12 ++++++------
> > >  1 file changed, 6 insertions(+), 6 deletions(-)
> > > 
> > > Index: linux-pm/drivers/acpi/processor_driver.c
> > > =================================================================
> > > ==
> > > --- linux-pm.orig/drivers/acpi/processor_driver.c
> > > +++ linux-pm/drivers/acpi/processor_driver.c
> > > @@ -263,6 +263,12 @@ static int __init acpi_processor_driver_
> > >       if (acpi_disabled)
> > >               return 0;
> > > 
> > > +     if
> > > (!cpufreq_register_notifier(&acpi_processor_notifier_block,
> > > +                                    CPUFREQ_POLICY_NOTIFIER)) {
> > > +             acpi_processor_cpufreq_init = true;
> > > +             acpi_processor_ignore_ppc_init();
> > > +     }
> > > +
> > >       result = driver_register(&acpi_processor_driver);
> > >       if (result < 0)
> > >               return result;
> > > @@ -276,12 +282,6 @@ static int __init acpi_processor_driver_
> > >       cpuhp_setup_state_nocalls(CPUHP_ACPI_CPUDRV_DEAD,
> > > "acpi/cpu-
> > > drv:dead",
> > >                                 NULL, acpi_soft_cpu_dead);
> > > 
> > > -     if
> > > (!cpufreq_register_notifier(&acpi_processor_notifier_block,
> > > -                                    CPUFREQ_POLICY_NOTIFIER)) {
> > > -             acpi_processor_cpufreq_init = true;
> > > -             acpi_processor_ignore_ppc_init();
> > > -     }
> > > -
> > >       acpi_processor_throttling_init();
> > >       return 0;
> > >  err:
> > > 
> > > 
> > >