linux-kernel - Re: [PATCH v2 7/7] cpufreq: CPPC: add autonomous mode boot parameter support

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Message-ID: <f9a1252d-25a0-4da8-9748-4b17798ed4e3@nvidia.com>
Date: Mon, 1 Sep 2025 18:48:46 +0530
From: Sumit Gupta <sumitg@...dia.com>
To: Randy Dunlap <rdunlap@...radead.org>, rafael@...nel.org,
 viresh.kumar@...aro.org, lenb@...nel.org, robert.moore@...el.com,
 corbet@....net, pierre.gondois@....com, zhenglifeng1@...wei.com,
 ray.huang@....com, gautham.shenoy@....com, mario.limonciello@....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
Cc: linux-tegra@...r.kernel.org, treding@...dia.com, jonathanh@...dia.com,
 vsethi@...dia.com, ksitaraman@...dia.com, sanjayc@...dia.com,
 bbasu@...dia.com, sumitg@...dia.com
Subject: Re: [PATCH v2 7/7] cpufreq: CPPC: add autonomous mode boot parameter
 support


On 24/08/25 05:38, Randy Dunlap wrote:
>
> On 8/23/25 1:01 PM, Sumit Gupta wrote:
>> Add kernel boot parameter 'cppc_cpufreq.auto_sel_mode' to enable CPPC
>> autonomous performance selection at system startup. When autonomous mode
>> is enabled, the hardware automatically adjusts CPU performance based on
>> workload demands using Energy Performance Preference (EPP) hints from
>> the OS.
>>
>> This parameter allows to configure the autonomous mode on all CPUs
>> without requiring runtime sysfs manipulation if the 'auto_sel' register
>> is present.
>>
>> When auto_sel_mode=1:
>> - All CPUs are configured for autonomous operation during driver init
>> - EPP is set to performance preference (0x0) by default
>> - Min/max performance bounds use defaults
>> - CPU frequency scaling is handled by hardware rather than OS
>>
>> Also ensure that when autonomous mode is active, the set_target callback
>> returns early since hardware controls frequency scaling directly.
>>
>> Signed-off-by: Sumit Gupta <sumitg@...dia.com>
>
>
>> ---
>>   .../admin-guide/kernel-parameters.txt         |  12 ++
>>   drivers/cpufreq/cppc_cpufreq.c                | 171 ++++++++++++++++--
>>   2 files changed, 168 insertions(+), 15 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index 86f395f2933b..ea58deb88c36 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -911,6 +911,18 @@
>>   			Format:
>>   			<first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
>>   
>> +	cppc_cpufreq.auto_sel_mode=
>> +			[CPU_FREQ] Autonomous Performance Level Selection.
>> +			When Autonomous selection is enabled, then the hardware is
>> +			allowed to autonomously select the CPU frequency.
>> +			In Autonomous mode, Energy Performance Preference(EPP)
>> +			provides input to the hardware to favour performance (0x0)
>> +			or energy efficiency (0xff).
>> +			Format: <bool>
>> +			Default: disabled.
>> +			0: force disabled
>> +			1: force enabled
>> +
>>   	cpuidle.off=1	[CPU_IDLE]
>>   			disable the cpuidle sub-system
>>   
>> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
>> index 5e1bbb5f67b8..bbf654c56ff9 100644
>> --- a/drivers/cpufreq/cppc_cpufreq.c
>> +++ b/drivers/cpufreq/cppc_cpufreq.c
> [snip]
>
>>   
>> +module_param(auto_sel_mode, bool, 0000);
> Hm. Is this changed to readable at some point or
> does it stay invisible?

Yes, it stays invisible. I am not sure about future as of now.

Thank you,
Sumit Gupta
>
>> +MODULE_PARM_DESC(auto_sel_mode, "Enable Autonomous Performance Level Selection");
>> +
>>   module_exit(cppc_cpufreq_exit);
>>   MODULE_AUTHOR("Ashwin Chaugule");
>>   MODULE_DESCRIPTION("CPUFreq driver based on the ACPI CPPC v5.0+ spec");
> For Documentation/:
> Reviewed-by: Randy Dunlap <rdunlap@...radead.org>
>
> Thanks.
>