linux-kernel - Re: [PATCH v6 02/14] x86/msr: add AMD CPPC MSR definitions

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Date:   Wed, 22 Dec 2021 19:05:40 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Huang Rui <ray.huang@....com>
Cc:     Borislav Petkov <bp@...e.de>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Giovanni Gherdovich <ggherdovich@...e.cz>,
        Steven Rostedt <rostedt@...dmis.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>,
        Steven Noonan <steven@...vesoftware.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 v6 02/14] x86/msr: add AMD CPPC MSR definitions

On Wed, Dec 22, 2021 at 1:17 AM Huang Rui <ray.huang@....com> wrote:
>
> Hi Boris,
>
> On Tue, Dec 21, 2021 at 11:45:09PM +0800, Borislav Petkov wrote:
> > On Mon, Dec 20, 2021 at 12:35:16AM +0800, Huang Rui wrote:
> >
> > Capitalize subject's first letter:
> >  [x86/msr: add AMD CPPC MSR definitions]
> >  [x86/msr: Add AMD CPPC MSR definitions]
>
> Thank you for the reply! Updated.
>
> >
> > > AMD CPPC (Collaborative Processor Performance Control) function uses MSR
> > > registers to manage the performance hints. So add the MSR register macro
> > > here.
> > >
> > > Signed-off-by: Huang Rui <ray.huang@....com>
> > > ---
> > >  arch/x86/include/asm/msr-index.h | 17 +++++++++++++++++
> > >  1 file changed, 17 insertions(+)
> > >
> > > diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> > > index 01e2650b9585..e7945ef6a8df 100644
> > > --- a/arch/x86/include/asm/msr-index.h
> > > +++ b/arch/x86/include/asm/msr-index.h
> > > @@ -486,6 +486,23 @@
> > >
> > >  #define MSR_AMD64_VIRT_SPEC_CTRL   0xc001011f
> > >
> > > +/* AMD Collaborative Processor Performance Control MSRs */
> > > +#define MSR_AMD_CPPC_CAP1          0xc00102b0
> > > +#define MSR_AMD_CPPC_ENABLE                0xc00102b1
> > > +#define MSR_AMD_CPPC_CAP2          0xc00102b2
> > > +#define MSR_AMD_CPPC_REQ           0xc00102b3
> > > +#define MSR_AMD_CPPC_STATUS                0xc00102b4
> > > +
> > > +#define CAP1_LOWEST_PERF(x)        (((x) >> 0) & 0xff)
> > > +#define CAP1_LOWNONLIN_PERF(x)     (((x) >> 8) & 0xff)
> > > +#define CAP1_NOMINAL_PERF(x)       (((x) >> 16) & 0xff)
> > > +#define CAP1_HIGHEST_PERF(x)       (((x) >> 24) & 0xff)
> > > +
> > > +#define REQ_MAX_PERF(x)            (((x) & 0xff) << 0)
> > > +#define REQ_MIN_PERF(x)            (((x) & 0xff) << 8)
> > > +#define REQ_DES_PERF(x)            (((x) & 0xff) << 16)
> > > +#define REQ_ENERGY_PERF_PREF(x)    (((x) & 0xff) << 24)
> >
> > All those bitfield names are too generic - they should at least be
> > prefixed with "CPPC_"
> >
> > If an Intel CPPC set of MSRs appears too, then the prefix should be
> > "AMD_CPPC_" and so on.
> >
>
> The similar function in Intel names HWP (Hardware P-State), and related MSR
> registers names as "HWP_" as the prefixes like below:
>
> /* IA32_HWP_CAPABILITIES */
> #define HWP_HIGHEST_PERF(x)             (((x) >> 0) & 0xff)
> #define HWP_GUARANTEED_PERF(x)          (((x) >> 8) & 0xff)
> #define HWP_MOSTEFFICIENT_PERF(x)       (((x) >> 16) & 0xff)
> #define HWP_LOWEST_PERF(x)              (((x) >> 24) & 0xff)
>
> Hi Rafael,
>
> Can we use the "CPPC_" as the prefixes for AMD CPPC MSR bitfield name?

Well, what about using "AMD_CPPC_" instead of "REQ_" in these names?
The names of the analogous Intel macros start with "HWP_" which
basically stands for "INTEL_CPPC_".