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

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Message-ID: <aRXR7yKyG6l1Agfq@arm.com>
Date: Thu, 13 Nov 2025 12:41:19 +0000
From: Ionela Voinescu <ionela.voinescu@....com>
To: Sumit Gupta <sumitg@...dia.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
Subject: Re: [PATCH v4 6/8] cpufreq: CPPC: Add sysfs for min/max_perf and
 perf_limited

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].

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.

> +
> +		This file is only present if the cppc-cpufreq driver is in use.
> +
> +What:		/sys/devices/system/cpu/cpuX/cpufreq/max_perf
> +Date:		December 2025
> +Contact:	linux-pm@...r.kernel.org
> +Description:	Maximum Performance Frequency
> +
> +		Read/write a frequency value in kHz from/to this file. This
> +		file conveys the maximum 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 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
> +
> +		This file is only present if the cppc-cpufreq driver is in use.
> +
> +What:		/sys/devices/system/cpu/cpuX/cpufreq/perf_limited
> +Date:		December 2025
> +Contact:	linux-pm@...r.kernel.org
> +Description:	Performance Limited
> +
> +		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
> -- 
> 2.34.1
>