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

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Message-ID: <acebbfddad686122c4aee9d1a87b048379dffbab.camel@gmail.com>
Date: Thu, 05 Feb 2026 15:10:09 +0200
From: Artem Bityutskiy <dedekind1@...il.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>, Sumit Gupta <sumitg@...dia.com>
Cc: viresh.kumar@...aro.org, pierre.gondois@....com,
 zhenglifeng1@...wei.com, 	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, 2026-02-03 at 13:43 +0100, Rafael J. Wysocki wrote:
> On Thu, Jan 29, 2026 at 11:49 AM Sumit Gupta <sumitg@...dia.com> wrote:
> > 
> > Add cppc_get/set_min_perf() and cppc_get/set_max_perf() APIs to read and
> > write the MIN_PERF and MAX_PERF registers.
> > 
> > Also add sysfs interfaces (min_perf, max_perf) in cppc_cpufreq driver
> > to expose these controls to userspace. The sysfs values are in frequency
> > (kHz) for consistency with other cpufreq sysfs files.
> 
> But this is not cpufreq and it is not consistent.

Just my 2 cents to add:

CPPC and Intel CPUs don't use kHz for performance scaling. We should
avoid introducing additional kHz-based interfaces where possible, since
the performance units <-> kHz translation may become more complex over
time than today. Future implementations could involve non-linear
relationships and reduced accuracy. Minimizing kHz interfaces now may
help reduce future work.

Thanks,
Artem.