linux-kernel - Re: [RFC PATCH 01/15] x86/apic: Fix 32-bit APIC initialization for extended Intel families

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Message-ID: <0553d913-0a8c-4508-9657-9b53b106f4bb@intel.com>
Date: Fri, 20 Dec 2024 15:13:39 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Sohil Mehta <sohil.mehta@...el.com>, x86@...nel.org,
 Dave Hansen <dave.hansen@...ux.intel.com>, Tony Luck <tony.luck@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
 Adrian Hunter <adrian.hunter@...el.com>,
 Kan Liang <kan.liang@...ux.intel.com>, Thomas Gleixner <tglx@...utronix.de>,
 Borislav Petkov <bp@...en8.de>, "H . Peter Anvin" <hpa@...or.com>,
 "Rafael J . Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
 Andy Lutomirski <luto@...nel.org>, Viresh Kumar <viresh.kumar@...aro.org>,
 Fenghua Yu <fenghua.yu@...el.com>, Jean Delvare <jdelvare@...e.com>,
 Guenter Roeck <linux@...ck-us.net>, Zhang Rui <rui.zhang@...el.com>,
 linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-acpi@...r.kernel.org, linux-pm@...r.kernel.org,
 linux-hwmon@...r.kernel.org
Subject: Re: [RFC PATCH 01/15] x86/apic: Fix 32-bit APIC initialization for
 extended Intel families

On 12/20/24 13:36, Sohil Mehta wrote:
> detect_init_APIC() limits the APIC detection to families 6 and 15.
> Extend the check to family numbers beyond 15. Also, convert it to a VFM
> check to make it simpler.

This changelog doesn't _quite_ fit the code. I'd rather it was a bit
more precise. It does not _just_ expand to "numbers beyond 15".

Also, It doesn't _really_ help to have the changelog tell us the
function name. That's why we have diff -p.  How about:

	APIC detection is currently limited to a few specific families
	and will not match the upcoming families >=18.

	Extend the check to include all families 6 or greater. Also
	convert it to a VFM check to make it simpler.

>  arch/x86/kernel/apic/apic.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index c5fb28e6451a..13dac8f78213 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -2014,8 +2014,8 @@ static bool __init detect_init_APIC(void)
>  	case X86_VENDOR_HYGON:
>  		break;
>  	case X86_VENDOR_INTEL:
> -		if (boot_cpu_data.x86 == 6 || boot_cpu_data.x86 == 15 ||
> -		    (boot_cpu_data.x86 == 5 && boot_cpu_has(X86_FEATURE_APIC)))
> +		if ((boot_cpu_data.x86 == 5 && boot_cpu_has(X86_FEATURE_APIC)) ||
> +		    boot_cpu_data.x86_vfm >= INTEL_PENTIUM_PRO)
>  			break;
>  		goto no_apic;
>  	default:

With that changelog tweak:

Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>