linux-kernel - Re: [PATCH v2 02/15] x86/cpu: Extract cpuid helpers to arch-independent

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Message-ID: <YVtRJiYD9EqGh7TM@zn.tnic>
Date:   Mon, 4 Oct 2021 21:08:22 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Iwona Winiarska <iwona.winiarska@...el.com>
Cc:     linux-kernel@...r.kernel.org, openbmc@...ts.ozlabs.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        x86@...nel.org, devicetree@...r.kernel.org,
        linux-aspeed@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org, linux-hwmon@...r.kernel.org,
        linux-doc@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>,
        Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Yazen Ghannam <yazen.ghannam@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jae Hyun Yoo <jae.hyun.yoo@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Zev Weiss <zweiss@...inix.com>,
        David Muller <d.mueller@...oft.ch>
Subject: Re: [PATCH v2 02/15] x86/cpu: Extract cpuid helpers to
 arch-independent

On Tue, Aug 03, 2021 at 01:31:21PM +0200, Iwona Winiarska wrote:
> Baseboard management controllers (BMC) often run Linux but are usually
> implemented with non-X86 processors. They can use PECI to access package
> config space (PCS) registers on the host CPU and since some information,
> e.g. figuring out the core count, can be obtained using different
> registers on different CPU generations, they need to decode the family
> and model.
> 
> The format of Package Identifier PCS register that describes CPUID
> information has the same layout as CPUID_1.EAX, so let's allow to reuse
> cpuid helpers by making it available for other architectures as well.
> 
> Signed-off-by: Iwona Winiarska <iwona.winiarska@...el.com>
> Reviewed-by: Tony Luck <tony.luck@...el.com>
> Reviewed-by: Dan Williams <dan.j.williams@...el.com>
> ---
>  MAINTAINERS                      | 1 +
>  arch/x86/Kconfig                 | 1 +
>  arch/x86/include/asm/cpu.h       | 3 ---
>  arch/x86/include/asm/microcode.h | 2 +-
>  arch/x86/kvm/cpuid.h             | 3 ++-
>  arch/x86/lib/Makefile            | 2 +-
>  drivers/edac/mce_amd.c           | 3 +--
>  include/linux/x86/cpu.h          | 9 +++++++++
>  lib/Kconfig                      | 4 ++++
>  lib/Makefile                     | 2 ++
>  lib/x86/Makefile                 | 3 +++
>  {arch/x86/lib => lib/x86}/cpu.c  | 2 +-
>  12 files changed, 26 insertions(+), 9 deletions(-)
>  create mode 100644 include/linux/x86/cpu.h
>  create mode 100644 lib/x86/Makefile
>  rename {arch/x86/lib => lib/x86}/cpu.c (95%)

AFAICT, all that churn is done for x86_family() and x86_model() which
are used *exactly* *once* and which are almost trivial anyway.

What's wrong with simply computing the family and model "by hand", so to
speak, in peci_device_info_init() and do away with that diffstat

 12 files changed, 26 insertions(+), 9 deletions(-)

?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette