linux-kernel - Re: [PATCH v4 6/8] cpufreq: CPPC: Add sysfs for min/max_perf and perf

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Message-ID: <dcf18694-515a-410e-94c6-b79039e31358@nvidia.com>
Date: Tue, 18 Nov 2025 16:16:54 +0530
From: Sumit Gupta <sumitg@...dia.com>
To: Ionela Voinescu <ionela.voinescu@....com>
Cc: rafael@...nel.org, viresh.kumar@...aro.org, lenb@...nel.org,
 robert.moore@...el.com, corbet@....net, pierre.gondois@....com,
 zhenglifeng1@...wei.com, 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, sumitg@...dia.com
Subject: Re: [PATCH v4 6/8] cpufreq: CPPC: Add sysfs for min/max_perf and
 perf_limited


On 13/11/25 18:11, Ionela Voinescu wrote:
> External email: Use caution opening links or attachments
>
>
> Hi,
>
> On Wednesday 05 Nov 2025 at 17:08:42 (+0530), 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      | 46 +++++++++++++++++++
>>   1 file changed, 46 insertions(+)
>>
>> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
>> index 8aed6d94c4cd..6f1f70696000 100644
>> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
>> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
>> @@ -327,6 +327,52 @@ 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:                December 2025
>> +Contact:     linux-pm@...r.kernel.org
>> +Description: Minimum Performance Frequency
>> +
>> +             Read/write a frequency value in kHz from/to this file. This
>> +             file conveys the minimum performance level (as frequency) at
>> +             which the platform may run. The frequency value is internally
>> +             converted to a performance value and must correspond to a
>> +             performance level in the range [Lowest Performance, Highest
>> +             Performance], inclusive. The minimum must be less than or equal
>> +             to the maximum performance. The performance range can be checked
>> +             from nodes:
>> +                     /sys/devices/system/cpu/cpuX/acpi_cppc/highest_perf
>> +                     /sys/devices/system/cpu/cpuX/acpi_cppc/lowest_perf
> I think information on highest/lowest performance is irrelevant here. If
> the user is expected to provide a frequency value, it should only care
> about it being in the range [cpuinfo_min_freq, cpuinfo_max_freq].

Will change it as below:

   Read/write a frequency value in kHz from/to this file. This
   file sets the minimum performance level (as frequency) at
   which the platform may run. The frequency value is internally
   converted to a performance value and must be in the range
   [cpuinfo_min_freq, cpuinfo_max_freq], inclusive.

   This file is only present if the cppc-cpufreq driver is in use.

> I think ideally all of these controls (auto-select, EPP, min, max, etc.)
> would have been better placed under
> /sys/devices/system/cpu/cpuX/acpi_cppc, but I suppose the intention
> was/is to have all performance related controls under cpufreq. But that
> means that the user should not be concerned about the underlying CPPC
> scale and only use /sys/devices/system/cpu/cpuX/acpi_cppc for
> information purposes.
>
> Thanks,
> Ionela.
>

In v1[1], added these controls under acpi_cppc sysfs.
Later after discussion, it was decided to keep them under cpufreq sysfs
and [2] was merged first.

[1] https://lore.kernel.org/lkml/20250211103737.447704-1-sumitg@nvidia.com/
[2] 
https://lore.kernel.org/all/20250507031941.2812701-1-zhenglifeng1@huawei.com/

Thank you,
Sumit Gupta