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

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Message-ID: <b7b137d2-373d-4705-851e-1b4bc99dae28@nvidia.com>
Date: Wed, 8 Oct 2025 15:46:29 +0530
From: Sumit Gupta <sumitg@...dia.com>
To: Mario Limonciello <superm1@...nel.org>, 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, 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,
 acpica-devel@...ts.linux.dev, linux-kernel@...r.kernel.org, sumitg@...dia.com
Subject: Re: [PATCH v3 6/8] cpufreq: CPPC: Add sysfs for min/max_perf and
 perf_limited


On 01/10/25 22:33, Mario Limonciello wrote:
> External email: Use caution opening links or attachments
>
>
> +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.

Sure.


>
> 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.

Ok, will add the info about these nodes as below.

  Minimum performance may be set to any performance
  value in the range [Lowest Performance, Highest Performance],
  inclusive but must be set to a value that is less than or
  equal to that specified by the Maximum Performance Register.
  The range can be checked from nodes:
    /sys/devices/system/cpu/cpuX/acpi_cppc/highest_perf
    /sys/devices/system/cpu/cpuX/acpi_cppc/lowest_perf

Thank you,
Sumit


>
>> +             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
>