linux-kernel - Re: [PATCH 4/6] x86/cpu: Add platform ID to CPU info structure

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Message-ID: <f71359e2-b506-42a3-bb3a-ba6112635131@intel.com>
Date: Tue, 20 Jan 2026 07:22:54 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Chao Gao <chao.gao@...el.com>, Dave Hansen <dave.hansen@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, sohil.mehta@...el.com,
 Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>,
 Ingo Molnar <mingo@...hat.com>, Jon Kohler <jon@...anix.com>,
 Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Thomas Gleixner <tglx@...nel.org>, Tony Luck <tony.luck@...el.com>,
 x86@...nel.org
Subject: Re: [PATCH 4/6] x86/cpu: Add platform ID to CPU info structure

On 1/19/26 19:14, Chao Gao wrote:
>> 	__u8			x86_stepping;
>> +	__u8			x86_platform_id; /* Intel-only. 3 bits */
> Tail comments are not preferred. I've seen tglx complain about them a few times.

Yeah, you're right. It doesn't fit well with the rest of the structure.
I'll fix it.

> Also, "3 bits" is misleading since x86_platform_id actually stores a bit mask.

Remember, there are two structures in play here. From the cover letter:

> Treat the platform ID as a peer of model/family/stepping. Store it
> in 'struct cpuinfo_x86', enable matching on it with with 'struct
> x86_cpu_id', and flesh out the 'old_microcode' list with it.

This hunk is patching 'cpuinfo_x86' which stores the 3 bits explicitly.

I think you're thinking of the mask in 'x86_cpu_id' which is used for
_matching_ this field in patch 5.

Could you double check that you're asking about the right structure,
please? I've certainly gotten the two structures mixed up before.