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

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Message-ID: <e9b4ae11-1fe3-a660-bb65-d3ba55ffcc56@amd.com>
Date:   Mon, 7 Dec 2020 16:07:52 -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 2:26 PM, Borislav Petkov wrote:
> On Mon, Dec 07, 2020 at 02:20:55PM -0600, Wei Huang wrote:
>> In summary, this patch is fine if Punit already verified it. My only
>> concern is the list can potentially increase over the time, and we will
>> keep coming back to fix override_acpi_psd() function.
> 
> Can the detection be done by looking at those _PSD things instead of
> comparing f/m/s?

Not I am aware of. I don't know the correlation between _PSD
configuration and CPU's f/m/s.

> 
> And, alternatively, what is this fixing?
> 
> So what if some zen2 boxes have correct _PSD objects? Why do they need
> to ignore the override?

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.

> 
> Hmmm?
>