linux-kernel - Re: [RFC PATCH 2/4] cpufreq: acpi-cpufreq: Add processor to the ignore PSD override list

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Message-ID: <8260faca-4a0d-8e06-c5ba-3ecdd0619e2f@amd.com>
Date:   Mon, 7 Dec 2020 21:44:42 -0600
From:   Wei Huang <whuang2@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Punit Agrawal <punitagrawal@...il.com>, rjw@...ysocki.net,
        wei.huang2@....com, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, x86@...nel.org
Subject: Re: [RFC PATCH 2/4] cpufreq: acpi-cpufreq: Add processor to the
 ignore PSD override list



On 12/7/20 4:30 PM, Borislav Petkov wrote:
> On Mon, Dec 07, 2020 at 04:07:52PM -0600, Wei Huang wrote:
>> I think we shouldn't override zen2 if _PSD is correct. In my opinion,
>> there are two approaches:
>>
>> * Keep override_acpi_psd()
>> Let us keep the original quirk and override_acpi_psd() function. Over
>> the time, people may want to add new CPUs to override_acpi_psd(). The
>> maintainer may declare that only CPUs >= family 17h will be fixed, to
>> avoid exploding the check-list.
>>
>> * Remove the quirk completely
>> We can completely remove commit acd316248205 ("acpi-cpufreq: Add quirk
>> to disable _PSD usage on all AMD CPUs")? I am not sure what "AMD desktop
>> boards" was referring to in the original commit message of acd316248205.
>> Maybe such machines aren't in use anymore.
> 
> * Third option: do not do anything. Why?

I am fine with this option, unless Punit can prove me that I am wrong,
(i.e. some Zen2 is broken because of acd316248205).

> 
> - Let sleeping dogs lie and leave the workaround acd316248205 for old
> machines.
> 
> - Make a clear cut that the override is not needed from Zen3 on, i.e.,
> your patch
> 
>    5368512abe08 ("acpi-cpufreq: Honor _PSD table setting on new AMD CPUs")
> 
> 
> Punit's commit message reads "...indicates that the override is not
> required for Zen3 onwards, it seems that domain information can be
> trusted even on certain earlier systems."
> 
> That's not nearly a justification in my book to do this on anything < Zen3.
> 
> This way you have a clear cut, you don't need to deal with adding any
> more models to override_acpi_psd() and all is good.
> 
> Unless there's a better reason to skip the override on machines < Zen3
> but I haven't heard any so far...
> 
> Thx.
>