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

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Message-ID: <08d527fd-4470-40bd-a458-5b4d52bcdc4d@intel.com>
Date: Tue, 20 Jan 2026 08:12:53 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Maciej Wieczor-Retman <m.wieczorretman@...me>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>, 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 1/20/26 08:03, Maciej Wieczor-Retman wrote:
> On 2026-01-20 at 07:13:31 -0800, Dave Hansen wrote:
>> On 1/20/26 06:34, Maciej Wieczor-Retman wrote:
>>>> 	__u8			x86_stepping;
>>>> +	__u8			x86_platform_id; /* Intel-only. 3 bits */
>>> Should platform ID be added to print_cpu_info()?
>>>
>>> So it's printed alongside (family: 0xN model: 0xN, stepping: 0xN)
>> It's not a horrible idea, but it's also relatively worthless compared to
>> the other three. I'd certainly take a look at it if someone sent a
>> patch, but I'm not really looking to add more to this series that
>> doesn't _need_ to be here.
> Fair enough, and I suppose if someone really needs this information they can
> just read the MSR themselves.

Right. If they get some weird "old_microcode" output, they can go use
rdmsr(1) to debug it if they're root. It might make debugging issues a
_wee_ bit easier to have the platform_id in dmesg, but it's only used in
two places in the kernel, so the value is *MUCH* lower than
family/model/stepping which are used all over.

Also, despite being 6 patches, this series is _just_ about as small as I
can make it to fix the bug at hand. Even if we decided a pr_whatever()
would be really nice, it's not a bug fix and would (IMNHO) need to be in
a separate series.