linux-kernel - Re: [PATCH] x86/tsc: Read AMD CPU frequency from Core::X86::Msr::PStateDef

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Message-ID: <20250814152550.GAaJ3__hIHnOBhKGWN@fat_crate.local>
Date: Thu, 14 Aug 2025 17:25:50 +0200
From: Borislav Petkov <bp@...en8.de>
To: Stephen Horvath <s.horvath@...look.com.au>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/tsc: Read AMD CPU frequency from
 Core::X86::Msr::PStateDef

On Wed, Aug 13, 2025 at 11:23:38AM +0000, Stephen Horvath wrote:
> +	/* The PPR defines the core multiplier as CpuFid * 25MHz */
> +	p0_freq = cpufid * 25;

As someone already pointed out:

PPR Vol 1 for AMD Family 1Ah Model 02h C1

...

MSRC001_006[4...B] [P-state [7:0]] (Core::X86::Msr::PStateDef)

...

CpuFid[11:0]: core frequency ID.

FFFh- <Value>*5
010h

So we need to do per-family checks here.

Not sure if that is worth it, frankly.

-- 
Regards/Gruss,
    Boris.

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