Re: [PATCH v4 6/8] cpufreq: CPPC: Add sysfs for min/max_perf and perf_limited

[Sumit Gupta]

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@xxxxxxxxxxxxx>
> > Signed-off-by: Sumit Gupta <sumitg@xxxxxxxxxx>
> > ---
> >   .../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@xxxxxxxxxxxxxxx
> > +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@xxxxxxxxxx/
[2] 
https://lore.kernel.org/all/20250507031941.2812701-1-zhenglifeng1@xxxxxxxxxx/

Thank you,
Sumit Gupta