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Date:   Wed, 21 Sep 2022 21:51:51 +0200
From:   Borislav Petkov <bp@alien8.de>
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     K Prateek Nayak <kprateek.nayak@amd.com>,
        linux-kernel@vger.kernel.org, rafael@kernel.org, lenb@kernel.org,
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        dave.hansen@linux.intel.com, tglx@linutronix.de, andi@lisas.de,
        puwen@hygon.cn, mario.limonciello@amd.com, peterz@infradead.org,
        rui.zhang@intel.com, gpiccoli@igalia.com,
        daniel.lezcano@linaro.org, ananth.narayan@amd.com,
        gautham.shenoy@amd.com, Calvin Ong <calvin.ong@amd.com>,
        stable@vger.kernel.org, regressions@lists.linux.dev
Subject: Re: [PATCH] ACPI: processor_idle: Skip dummy wait for processors
 based on the Zen microarchitecture
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 <2b6143b6-9db4-05bc-1e8d-c5d129126f99@intel.com>
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On Wed, Sep 21, 2022 at 07:15:07AM -0700, Dave Hansen wrote:
> In the end, the delay is because of buggy, circa 2006 chipsets?  So, we
> use a CPU vendor specific check to approximate that the chipset is
> recent and not affected by the bug?  If so, is there no better way to
> check for a newer chipset than this?

So I did some git archeology but that particular addition is in some
conglomerate, glued-together patch from 2007 which added the cpuidle
tree:

commit 4f86d3a8e297205780cca027e974fd5f81064780
Author: Len Brown <len.brown@intel.com>
Date:   Wed Oct 3 18:58:00 2007 -0400

    cpuidle: consolidate 2.6.22 cpuidle branch into one patch


so the most precise check here should be to limit that dummy read to
that Intel chipset which needed it. Damned if I knew how to figure out
which...

-- 
Regards/Gruss,
    Boris.

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