linux-kernel - Re: [PATCH 02/49] x86/cpu: Describe hybrid CPUs in cpuinfo

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Date:   Mon, 8 Feb 2021 18:56:40 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     kan.liang@...ux.intel.com
Cc:     peterz@...radead.org, acme@...nel.org, mingo@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de,
        namhyung@...nel.org, jolsa@...hat.com, ak@...ux.intel.com,
        yao.jin@...ux.intel.com, alexander.shishkin@...ux.intel.com,
        adrian.hunter@...el.com,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <len.brown@...el.com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH 02/49] x86/cpu: Describe hybrid CPUs in cpuinfo_x86

On Mon, Feb 08, 2021 at 07:24:59AM -0800, kan.liang@...ux.intel.com wrote:
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index c20a52b..1f25ac9 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -139,6 +139,16 @@ struct cpuinfo_x86 {
>  	u32			microcode;
>  	/* Address space bits used by the cache internally */
>  	u8			x86_cache_bits;
> +	/*
> +	 * In hybrid processors, there is a CPU type and a native model ID. The
> +	 * CPU type (x86_cpu_type[31:24]) describes the type of micro-
> +	 * architecture families. The native model ID (x86_cpu_type[23:0])
> +	 * describes a specific microarchitecture version. Combining both
> +	 * allows to uniquely identify a CPU.
> +	 *
> +	 * Please note that the native model ID is not related to x86_model.
> +	 */
> +	u32			x86_cpu_type;

Why are you adding it here instead of simply using
X86_FEATURE_HYBRID_CPU at the call site?

How many uses in this patchset?

/me searches...

Exactly one.

Just query X86_FEATURE_HYBRID_CPU at the call site and read what you
need from CPUID and use it there - no need for this.

Thx.

-- 
Regards/Gruss,
    Boris.

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