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

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Message-ID: <CAJZ5v0hUdLsh8UK5G6rHHD49RQGYLAiU1J-11DK-fLTKnuqhUQ@mail.gmail.com>
Date: Tue, 3 Feb 2026 13:45:09 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Sumit Gupta <sumitg@...dia.com>
Cc: Russell Haley <yumpusamongus@...il.com>, "zhenglifeng (A)" <zhenglifeng1@...wei.com>, 
	pierre.gondois@....com, "Rafael J. Wysocki" <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 Tue, Feb 3, 2026 at 10:41 AM Sumit Gupta <sumitg@...dia.com> wrote:
>
> >>> 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
>
> I can rename to either of the below:
> - min/max_freq: might be confused with scaling_min/max_freq.
> - min/max_perf_freq: keeps the CPPC register association clear.
>
> Rafael, Any preferences here?

On x86 the units in CPPC are not kHz and there is no easy reliable way
to convert them to kHz.

Everything under /sys/devices/system/cpu/cpu0/acpi_cppc/ needs to be
in CPPC units, not kHz (unless, of course, kHz are CPPC units).