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

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Date:   Mon, 11 Oct 2021 19:32:38 +0000
From:   "Winiarska, Iwona" <iwona.winiarska@...el.com>
To:     "bp@...en8.de" <bp@...en8.de>
CC:     "corbet@....net" <corbet@....net>,
        "jae.hyun.yoo@...ux.intel.com" <jae.hyun.yoo@...ux.intel.com>,
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        "andrew@...id.au" <andrew@...id.au>,
        "Luck, Tony" <tony.luck@...el.com>,
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        "Williams, Dan J" <dan.j.williams@...el.com>
Subject: Re: [PATCH v2 02/15] x86/cpu: Extract cpuid helpers to
 arch-independent

On Mon, 2021-10-04 at 21:08 +0200, Borislav Petkov wrote:
> 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.

Correct.

> 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(-)
> 
> ?

Nothing wrong - just a trade-off between churn and keeping things tidy and not
duplicated, similar to patch 1.
And just like in patch 1, if you have a strong opinion against it - we can
duplicate. 

Thanks
-Iwona