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

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Message-ID: <d35459bc-cf52-4fd5-886a-e9f6db7fda5e@infradead.org>
Date: Sat, 23 Aug 2025 17:08:05 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: Sumit Gupta <sumitg@...dia.com>, 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
Subject: Re: [PATCH v2 7/7] cpufreq: CPPC: add autonomous mode boot parameter
 support



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?

> +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.

-- 
~Randy