linux-kernel - RE: [PATCH v2 03/21] ACPI: CPPC: Check online CPUs for determining

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Date:   Wed, 20 Oct 2021 11:15:26 +0000
From:   "Huang, Ray" <Ray.Huang@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
CC:     "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Borislav Petkov <bp@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        "Sharma, Deepak" <Deepak.Sharma@....com>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        "Limonciello, Mario" <Mario.Limonciello@....com>,
        "Fontenot, Nathan" <Nathan.Fontenot@....com>,
        "Su, Jinzhou (Joe)" <Jinzhou.Su@....com>,
        "Du, Xiaojian" <Xiaojian.Du@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: RE: [PATCH v2 03/21] ACPI: CPPC: Check online CPUs for determining
 _CPC is valid

[AMD Official Use Only]

> -----Original Message-----
> From: Rafael J. Wysocki <rafael@...nel.org>
> Sent: Wednesday, October 20, 2021 12:53 AM
> To: Huang, Ray <Ray.Huang@....com>
> Cc: Rafael J . Wysocki <rafael.j.wysocki@...el.com>; Viresh Kumar
> <viresh.kumar@...aro.org>; Shuah Khan <skhan@...uxfoundation.org>;
> Borislav Petkov <bp@...e.de>; Peter Zijlstra <peterz@...radead.org>; Ingo
> Molnar <mingo@...nel.org>; Linux PM <linux-pm@...r.kernel.org>;
> Sharma, Deepak <Deepak.Sharma@....com>; Deucher, Alexander
> <Alexander.Deucher@....com>; Limonciello, Mario
> <Mario.Limonciello@....com>; Fontenot, Nathan
> <Nathan.Fontenot@....com>; Su, Jinzhou (Joe) <Jinzhou.Su@....com>;
> Du, Xiaojian <Xiaojian.Du@....com>; Linux Kernel Mailing List <linux-
> kernel@...r.kernel.org>; the arch/x86 maintainers <x86@...nel.org>
> Subject: Re: [PATCH v2 03/21] ACPI: CPPC: Check online CPUs for
> determining _CPC is valid
> 
> On Sun, Sep 26, 2021 at 11:06 AM Huang Rui <ray.huang@....com> wrote:
> >
> > From: Mario Limonciello <mario.limonciello@....com>
> >
> > As this is a static check, it should be based upon what is currently
> > present on the system. This makes probeing more deterministic.
> >
> > While local APIC flags field (lapic_flags) of cpu core in MADT table
> > is 0, then the cpu core won't be enabled. In this case, _CPC won't be
> > found in this core, and return back to _CPC invalid with walking
> > through possible cpus (include disable cpus). This is not expected, so
> > switch to check online CPUs instead.
> >
> > Reported-by: Jinzhou Su <Jinzhou.Su@....com>
> > Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> > Signed-off-by: Huang Rui <ray.huang@....com>
> > ---
> >  drivers/acpi/cppc_acpi.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c index
> > a4d4eebba1da..2efe2ba97d96 100644
> > --- a/drivers/acpi/cppc_acpi.c
> > +++ b/drivers/acpi/cppc_acpi.c
> > @@ -411,7 +411,7 @@ bool acpi_cpc_valid(void)
> >         struct cpc_desc *cpc_ptr;
> >         int cpu;
> >
> > -       for_each_possible_cpu(cpu) {
> > +       for_each_online_cpu(cpu) {
> 
> Shouldn't this be for_each_present_cpu()?  In case a CPU is present, but not
> online when cppc_cpufreq is loaded?
> 

OK, got it, thanks! Will update it in V3.

Thanks,
Ray