linux-kernel - Re: [PATCH v3 6/8] cpufreq: CPPC: Add sysfs for min/max_perf and perf

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Message-ID: <dbee61be-4e1c-4f58-ae20-32447b6767fd@kernel.org>
Date: Wed, 1 Oct 2025 12:03:40 -0500
From: Mario Limonciello <superm1@...nel.org>
To: linux-doc@...r.kernel.org, corbet@....net,
 Randy Dunlap <rdunlap@...radead.org>
Cc: linux-tegra@...r.kernel.org, treding@...dia.com, jonathanh@...dia.com,
 vsethi@...dia.com, ksitaraman@...dia.com, sanjayc@...dia.com,
 bbasu@...dia.com, Sumit Gupta <sumitg@...dia.com>, rafael@...nel.org,
 viresh.kumar@...aro.org, lenb@...nel.org, robert.moore@...el.com,
 pierre.gondois@....com, zhenglifeng1@...wei.com, ray.huang@....com,
 gautham.shenoy@....com, perry.yuan@....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
Subject: Re: [PATCH v3 6/8] cpufreq: CPPC: Add sysfs for min/max_perf and
 perf_limited

+linux-doc

On 10/1/25 10:01 AM, Sumit Gupta wrote:
> Add sysfs interfaces for Minimum Performance, Maximum Performance
> and Performance Limited Register in the cppc_cpufreq driver.
> 
> Reviewed-by: Randy Dunlap <rdunlap@...radead.org>
> Signed-off-by: Sumit Gupta <sumitg@...dia.com>
> ---
>   .../ABI/testing/sysfs-devices-system-cpu      | 43 +++++++++++++++++++
>   1 file changed, 43 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> index ab8cd337f43a..82141b45d58c 100644
> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> @@ -327,6 +327,49 @@ Description:	Energy performance preference
>   
>   		This file is only present if the cppc-cpufreq driver is in use.
>   
> +What:		/sys/devices/system/cpu/cpuX/cpufreq/min_perf
> +Date:		September 2025

These dates will need to push out since this isn't 6.17 material.

That being said I have a general question to linux-doc.

Why is this is date based?  I would expect a date is meaningless to 
anyone reads this documentation.  People who want to know if an 
interface is available would normally look at their kernel version to tell.

So wouldn't it make more sense for this field to be something like:

Version: 6.19

> +Contact:	linux-pm@...r.kernel.org
> +Description:	Minimum Performance
> +
> +		Read/write a 32 bits value from/to this file. This file
> +		conveys the minimum performance level at which the platform
> +		may run. Minimum performance may be set to any performance
> +		value in the range [Lowest Performance, Highest Performance],

How will a user discover the lowest -> highest range?

IE I think you should document how to lookup those caps too.

> +		inclusive but must be set to a value that is less than or
> +		equal to that specified by the Maximum Performance Register.
> +
> +		Writing to this file only has meaning when Autonomous Selection
> +		is enabled.
> +
> +		This file is only present if the cppc-cpufreq driver is in use.
> +
> +What:		/sys/devices/system/cpu/cpuX/cpufreq/max_perf
> +Date:		September 2025
> +Contact:	linux-pm@...r.kernel.org
> +Description:	Minimum Performance
> +
> +		Read/write a 32 bits value from/to this file. This file conveys
> +		the maximum performance level at which the platform may run.
> +		Maximum performance may be set to any performance value in the
> +		range [Lowest Performance, Highest Performance], inclusive.
> +
> +		Writing to this file only has meaning when Autonomous Selection is
> +		enabled.
> +
> +		This file is only present if the cppc-cpufreq driver is in use.
> +
> +What:		/sys/devices/system/cpu/cpuX/cpufreq/perf_limited
> +Date:		September 2025
> +Contact:	linux-pm@...r.kernel.org
> +Description:	Minimum Performance
> +
> +		Read/write a 32 bits value from/to this file. This file indicates
> +		to OSPM that an unpredictable event has limited processor
> +		performance, and the delivered performance may be less than
> +		desired/minimum performance.
> +
> +		This file is only present if the cppc-cpufreq driver is in use.
>   
>   What:		/sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
>   Date:		August 2008