linux-kernel - Re: [PATCH v7 4/7] ACPI: CPPC: add APIs and sysfs interface for min/max

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Message-ID: <74f3e6cf-7c13-43e6-a8f6-2b46184b8ad6@gmail.com>
Date: Mon, 2 Feb 2026 19:36:14 -0600
From: Russell Haley <yumpusamongus@...il.com>
To: Sumit Gupta <sumitg@...dia.com>, "zhenglifeng (A)"
 <zhenglifeng1@...wei.com>, pierre.gondois@....com
Cc: rafael@...nel.org, viresh.kumar@...aro.org, ionela.voinescu@....com,
 lenb@...nel.org, robert.moore@...el.com, corbet@....net,
 rdunlap@...radead.org, ray.huang@....com, gautham.shenoy@....com,
 mario.limonciello@....com, perry.yuan@....com, zhanjie9@...ilicon.com,
 linux-pm@...r.kernel.org, linux-acpi@...r.kernel.org,
 linux-doc@...r.kernel.org, acpica-devel@...ts.linux.dev,
 linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
 treding@...dia.com, jonathanh@...dia.com, vsethi@...dia.com,
 ksitaraman@...dia.com, sanjayc@...dia.com, nhartman@...dia.com,
 bbasu@...dia.com
Subject: Re: [PATCH v7 4/7] ACPI: CPPC: add APIs and sysfs interface for
 min/max_perf

On 1/31/26 7:58 AM, Sumit Gupta wrote:
> 
> On 31/01/26 09:36, zhenglifeng (A) wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> Hi Sumit,
>>
>> I am thinking that maybe it is better to call these two sysfs interface
>> 'min_freq' and 'max_freq' as users read and write khz instead of raw
>> value.
> 
> Thanks for the suggestion.
> Kept min_perf/max_perf to match the CPPC register names
> (MIN_PERF/MAX_PERF), making it clear to users familiar with
> CPPC what's being controlled.
> The kHz unit is documented in the ABI.
> 
> Thank you,
> Sumit Gupta

On my x86 machine with kernel 6.18.5, the kernel is exposing raw values:

> grep . /sys/devices/system/cpu/cpu0/acpi_cppc/*
/sys/devices/system/cpu/cpu0/acpi_cppc/feedback_ctrs:ref:342904018856568
del:437439724183386
/sys/devices/system/cpu/cpu0/acpi_cppc/guaranteed_perf:63
/sys/devices/system/cpu/cpu0/acpi_cppc/highest_perf:88
/sys/devices/system/cpu/cpu0/acpi_cppc/lowest_freq:0
/sys/devices/system/cpu/cpu0/acpi_cppc/lowest_nonlinear_perf:36
/sys/devices/system/cpu/cpu0/acpi_cppc/lowest_perf:1
/sys/devices/system/cpu/cpu0/acpi_cppc/nominal_freq:3900
/sys/devices/system/cpu/cpu0/acpi_cppc/nominal_perf:62
/sys/devices/system/cpu/cpu0/acpi_cppc/reference_perf:62
/sys/devices/system/cpu/cpu0/acpi_cppc/wraparound_time:18446744073709551615

It would be surprising for a nearby sysfs interface with very similar
names to use kHz instead.

Thanks,

Russell Haley