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

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Message-ID: <CAJZ5v0ggzD0PEti-r20Sm-8n0gPigPh=NgE2Oa=UKzMmwB0jpw@mail.gmail.com>
Date: Tue, 3 Feb 2026 13:54:21 +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, viresh.kumar@...aro.org, ionela.voinescu@....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 1:45 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> 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).

That said, the new attributes will show up elsewhere.

So why do you need to add these things in the first place?