linux-kernel - Re: [PATCH v2] x86,acpi: Limit "Dummy wait" workaround to older AMD and Intel processors

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Message-ID: <YzIDyLbGgzEv0wzP@rhlx01.hs-esslingen.de>
Date:   Mon, 26 Sep 2022 21:55:52 +0200
From:   Andreas Mohr <andi@...as.de>
To:     K Prateek Nayak <kprateek.nayak@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, rafael@...nel.org, lenb@...nel.org,
        linux-acpi@...r.kernel.org, linux-pm@...r.kernel.org,
        dave.hansen@...ux.intel.com, bp@...en8.de, tglx@...utronix.de,
        andi@...as.de, puwen@...on.cn, mario.limonciello@....com,
        rui.zhang@...el.com, gpiccoli@...lia.com,
        daniel.lezcano@...aro.org, ananth.narayan@....com,
        gautham.shenoy@....com, Calvin Ong <calvin.ong@....com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] x86,acpi: Limit "Dummy wait" workaround to older AMD
 and Intel processors

Hi,

Am Mon, Sep 26, 2022 at 10:02:44PM +0530 schrieb K Prateek Nayak:
> Hello Peter,
> 
> On 9/26/2022 5:37 PM, Peter Zijlstra wrote:
> > For how many of the above have you changed behaviour?
> 
> The proposed logic does alter the behavior for x86 chipsets that depend
> on acpi_idle driver and have IOPORT based C-state. Based on what
> Rafael and Dave suggested, I have marked all Intel processors to be
> affected by this bug. In light of Andreas' report, I've also marked
> all the pre-family 17h AMD processors to be affected by this bug to avoid
> causing any regression.
> 
> It is hard to tell if any other vendor had this bug in their chipsets.
> Dave's patch does not make this consideration either and limits the
> dummy operation to only Intel chipsets using acpi_idle driver.
> (https://lore.kernel.org/all/78d13a19-2806-c8af-573e-7f2625edfab8@intel.com/)
> If folks reported a regression, I would have been happy to fix it for
> them.

Despite certain, umm, controversies, the discussion/patch activities
appear to be heading into a good direction ;)



This text somehow prompted me to think of
whether STPCLK# [quirk] behaviour is
a property of the CPU family, or the chipset, or actually a combination of it.

Given that [from recollection] VIA 8233/8235 spec PDFs do mention STPCLK#,
possibly a chipset does have a say in it? (which
obviously would then mean that
the kernel's quirk state decision-making would have to be refined)

Minor reference (note 8237, not 8233):
http://www.chipset-ic.com/datasheet/VT8237.pdf
  "STPCLK# is asserted by the VT8237R to the CPU to throttle the processor."
  (and many other STPCLK# mentions there)

Greetings

Andreas Mohr