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otherwise initialize from caps >>>>>> - Initialize desired_perf to max_perf as a starting hint >>>>>> - Hardware controls frequency instead of the OS governor >>>>>> - EPP behavior depends on parameter value: >>>>>>    - performance (or 1): override EPP to performance preference >>>>>> (0x0) >>>>>>    - default_epp (or 2): preserve EPP value programmed by BIOS/ >>>>>> firmware >>>>>> >>>>>> The boot parameter is applied only during first policy >>>>>> initialization. >>>>>> Skip applying it on CPU hotplug to preserve runtime sysfs >>>>>> configuration. >>>>>> >>>>>> This patch depends on patch series [1] ("cpufreq: Set policy->min >>>>>> and >>>>>> max as real QoS constraints") so that the policy->min/max set in >>>>>> cppc_cpufreq_cpu_init() are not overridden by cpufreq_set_policy() >>>>>> during init. >>>>>> >>>>>> Signed-off-by: Sumit Gupta >>>>>> --- >>>>>> [1] https://lore.kernel.org/lkml/20260511135538.522653-1- >>>>>> pierre.gondois@arm.com/ >>>>>> --- >>>>>>   .../admin-guide/kernel-parameters.txt         |  16 +++ >>>>>>   drivers/cpufreq/cppc_cpufreq.c                | 122 +++++++++++++ >>>>>> ++++- >>>>>>   2 files changed, 133 insertions(+), 5 deletions(-) >>>>>> >>>>>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/ >>>>>> Documentation/admin-guide/kernel-parameters.txt >>>>>> index 0eb64aab3685..7e4b3a8fd76f 100644 >>>>>> --- a/Documentation/admin-guide/kernel-parameters.txt >>>>>> +++ b/Documentation/admin-guide/kernel-parameters.txt >>>>>> @@ -1048,6 +1048,22 @@ Kernel parameters >>>>>>                       policy to use. This governor must be >>>>>> registered >>>>>> in the >>>>>>                       kernel before the cpufreq driver probes. >>>>>> >>>>>> +     cppc_cpufreq.auto_sel_mode= >>>>>> +                     [CPU_FREQ] Enable ACPI CPPC autonomous >>>>>> performance >>>>>> +                     selection. When enabled, hardware >>>>>> automatically >>>>>> adjusts >>>>>> +                     CPU frequency on all CPUs based on workload >>>>>> demands. >>>>>> +                     In Autonomous mode, Energy Performance >>>>>> Preference (EPP) >>>>>> +                     hints guide hardware toward performance (0x0) >>>>>> or energy >>>>>> +                     efficiency (0xff). >>>>>> +                     Requires ACPI CPPC autonomous selection >>>>>> register >>>>>> +                     support. >>>>>> +                     Accepts: >>>>>> +                       performance, 1: enable auto_sel + set EPP to >>>>>> +                                       performance (0x0) >>>>>> +                       default_epp, 2: enable auto_sel, preserve >>>>>> EPP >>>>>> value >>>>>> +                                       programmed by BIOS/firmware >>>>>> +                     Unset: cpufreq governors are used (auto_sel >>>>>> disabled). >>>>> >>>>> Rather than unset doing nothing, have you considered having it take a >>>>> midpoint like 128?  That's what we do in amd-pstate (default to >>>>> balance_performance).  I think it turns into a reasonable balance. >>>> >>>> Thanks for the suggestion. >>>> I can add balance_performance that enables auto_sel with EPP=128 in >>>> v4. >>>> >>>> On changing the driver default (no param behavior) to auto enable >>>> balance_performance, it would be good to keep the current behavior for >>>> now since cppc_cpufreq is generic across ARM64/RISC-V platforms where >>>> EPP and Autonomous Selection registers are optional. >>>> A default change would affect existing users relying on governors. >>>> >>>> Thank you, >>>> Sumit Gupta >>> >>> But couldn't you make the "no module parameter set" follow the behavior >>> to only set the registers if they're available? >>> >>> So the systems that support it start using it, the ones that don't it's >>> a NOP. >>> >> >> Would it work to add balance_performance as a new mode in v4, >> and discuss changing the default separately as a follow-up? >> > > Sure. > >> Runtime detection helps for unsupported platforms. But platforms which >> support the registers use OS governors today, and silently switching >> them to autonomous mode on a kernel update is a behavior change for >> existing users. They would also have no way to boot into sw governor. >> > > But hopefully it should be better battery life/responsiveness for those > scenarios too, right? > Yes in many cases, but if some workloads rely on specific OS governor configurations, then that would get impacted. I will send a separate change later to seek broader consensus on enabling auto_sel as default without any param. Thank you, Sumit Gupta ....