linux-kernel - Re: [PATCH 01/19] x86/cpufreatures: add AMD CPPC extension feature flag

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Date:   Mon, 13 Sep 2021 17:48:51 +0800
From:   Huang Rui <ray.huang@....com>
To:     Borislav Petkov <bp@...en8.de>
CC:     "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        "Ingo Molnar" <mingo@...nel.org>,
        "linux-pm@...r.kernel.org" <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@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH 01/19] x86/cpufreatures: add AMD CPPC extension feature
 flag

Hi Boris,

On Fri, Sep 10, 2021 at 01:58:19AM +0800, Borislav Petkov wrote:
> On Wed, Sep 08, 2021 at 10:59:43PM +0800, Huang Rui wrote:
> > Add Collaborative Processor Performance Control Extension feature flag
> > for AMD processors.
> > 
> > Signed-off-by: Huang Rui <ray.huang@....com>
> > ---
> >  arch/x86/include/asm/cpufeatures.h | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> > index d0ce5cfd3ac1..f7aea50e3371 100644
> > --- a/arch/x86/include/asm/cpufeatures.h
> > +++ b/arch/x86/include/asm/cpufeatures.h
> > @@ -313,6 +313,7 @@
> >  #define X86_FEATURE_AMD_SSBD		(13*32+24) /* "" Speculative Store Bypass Disable */
> >  #define X86_FEATURE_VIRT_SSBD		(13*32+25) /* Virtualized Speculative Store Bypass Disable */
> >  #define X86_FEATURE_AMD_SSB_NO		(13*32+26) /* "" Speculative Store Bypass is fixed in hardware. */
> > +#define X86_FEATURE_AMD_CPPC_EXT	(13*32+27) /* Collaborative Processor Performance Control Extension */
> 
> Why not simply X86_FEATURE_AMD_CPPC ?

This feature flag indicates the full MSR hardware solution of AMD P-States,
if it is not set, that means we will go with in shared memory hardware
solution. So we name this as extension. I will explain the details in the
commit log at V2. ;-)

Thanks,
Ray