Re: [PATCH v4 8/8] cpufreq: CPPC: add autonomous mode boot parameter support

[Sumit Gupta <sumitg@nvidia.com>]

On 27/11/25 20:23, Pierre Gondois wrote:
> External email: Use caution opening links or attachments
>
>
> On 11/5/25 12:38, 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.
>>
>> 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 module init
>> - EPP is set to performance preference (0x0) by default
>> - Min/max performance bounds use defaults
>> - CPU frequency scaling is handled by hardware instead of OS governor
>>
>> For Documentation/:
>> Reviewed-by: Randy Dunlap<rdunlap@infradead.org>
>> Signed-off-by: Sumit Gupta<sumitg@nvidia.com>
>> ---
>>   .../admin-guide/kernel-parameters.txt         |  12 ++
>>   drivers/cpufreq/cppc_cpufreq.c                | 197 +++++++++++++++---
>>   2 files changed, 182 insertions(+), 27 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt 
>> b/Documentation/admin-guide/kernel-parameters.txt
>> index b8f8f5d74093..048f84008a7e 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -929,6 +929,18 @@
>>                       Format:
>> <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
>>
>> +     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.
>> +                     Format: <bool>
>> +                     Default: 0 (disabled)
>> +                     0: use cpufreq governors
>> +                     1: enable if supoorted by hardware
>> +
>>       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 d1b44beaddda..0a55ab011317 100644
>> --- a/drivers/cpufreq/cppc_cpufreq.c
>> +++ b/drivers/cpufreq/cppc_cpufreq.c
>> @@ -28,8 +28,12 @@
>>   #include <acpi/cppc_acpi.h>
>>
>>   static struct cpufreq_driver cppc_cpufreq_driver;
>> +
>>   static DEFINE_MUTEX(cppc_cpufreq_update_autosel_config_lock);
>>
>> +/* Autonomous Selection */
>> +static bool auto_sel_mode;
>> +
>>   #ifdef CONFIG_ACPI_CPPC_CPUFREQ_FIE
>>   static enum {
>>       FIE_UNSET = -1,
>> @@ -272,8 +276,13 @@ static int cppc_cpufreq_set_target(struct 
>> cpufreq_policy *policy,
>>       freqs.old = policy->cur;
>>       freqs.new = target_freq;
>>
>> +     /*
>> +      * In autonomous selection mode, hardware handles frequency 
>> scaling directly
>> +      * based on workload and EPP hints. So, skip the OS frequency 
>> set requests.
>> +      */
>>       cpufreq_freq_transition_begin(policy, &freqs);
>> -     ret = cppc_set_perf(cpu, &cpu_data->perf_ctrls);
>> +     if (!cpu_data->perf_caps.auto_sel)
>> +             ret = cppc_set_perf(cpu, &cpu_data->perf_ctrls);
>>       cpufreq_freq_transition_end(policy, &freqs, ret != 0);
>>
>>       if (ret)
>> @@ -565,6 +574,12 @@ static struct cppc_cpudata 
>> *cppc_cpufreq_get_cpu_data(unsigned int cpu)
>>               goto free_mask;
>>       }
>>
>> +     ret = cppc_get_perf(cpu, &cpu_data->perf_ctrls);
>> +     if (ret) {
>> +             pr_debug("Err reading CPU%d perf ctrls:ret:%d\n", cpu, 
>> ret);
>> +             goto free_mask;
>> +     }
>> +
>>       return cpu_data;
>>
>>   free_mask:
>> @@ -666,11 +681,81 @@ static int 
>> cppc_cpufreq_update_autosel_val(struct cpufreq_policy *policy, bool a
>>       return 0;
>>   }
>>
>> +static int cppc_cpufreq_update_epp_val(struct cpufreq_policy 
>> *policy, u32 epp)
>> +{
>> +     struct cppc_cpudata *cpu_data = policy->driver_data;
>> +     unsigned int cpu = policy->cpu;
>> +     int ret;
>> +
>> +     pr_debug("cpu%d, eppcurr:%u,new:%u\n", cpu, 
>> cpu_data->perf_ctrls.energy_perf, epp);
>> +
>> + guard(mutex)(&cppc_cpufreq_update_autosel_config_lock);
> Do we need to take the mutex ? Or is it reserved to auto_sel ?

Will move this to parent function.
Explained more in reply of the previous patch '7/8'.

>> +
>> +     ret = cppc_set_epp(cpu, epp);
>> +     if (ret) {
>> +             pr_warn("failed to set energy_perf forcpu:%d (%d)\n", 
>> cpu, ret);
>> +             return ret;
>> +     }
>> +     cpu_data->perf_ctrls.energy_perf = epp;
>> +
>> +     return 0;
>> +}
>> +
>> +/**
>> + * cppc_cpufreq_update_autosel_config - Update Autonomous selection 
>> configuration
>> + * @policy: cpufreq policy for the CPU
>> + * @min_perf: minimum performance value to set
>> + * @max_perf: maximum performance value to set
>> + * @auto_sel: autonomous selection mode enable/disable (also 
>> controls min/max perf reg updates)
>> + * @epp_val: energy performance preference value
>> + * @update_epp: whether to update EPP register
>> + * @update_policy: whether to update policy constraints
>> + *
>> + * Return: 0 on success, negative error code on failure
>> + */
>> +static int cppc_cpufreq_update_autosel_config(struct cpufreq_policy 
>> *policy,
>> +                                           u64 min_perf, u64 
>> max_perf, bool auto_sel,
>> +                                           u32 epp_val, bool 
>> update_epp, bool update_policy)
>> +{
>> +     const unsigned int cpu = policy->cpu;
>> +     int ret;
>> +
>> +     /*
>> +      * Set min/max performance registers and update policy 
>> constraints.
>> +      *   When enabling: update both registers and policy.
>> +      *   When disabling: update policy only.
>> +      * Continue even if min/max are not supported, as EPP and autosel
>> +      * might still be supported.
>> +      */
>> +     ret = cppc_cpufreq_set_min_perf(policy, min_perf, auto_sel, 
>> update_policy);
>> +     if (ret && ret != -EOPNOTSUPP)
>> +             return ret;
>> +
>> +     ret = cppc_cpufreq_set_max_perf(policy, max_perf, auto_sel, 
>> update_policy);
>> +     if (ret && ret != -EOPNOTSUPP)
>> +             return ret;
>> +
>> +     if (update_epp) {
>> +             ret = cppc_cpufreq_update_epp_val(policy, epp_val);
>> +             if (ret)
>> +                     return ret;
>> +     }
>> +
>> +     ret = cppc_cpufreq_update_autosel_val(policy, auto_sel);
>> +     if (ret)
>> +             return ret;
>> +
>> +     pr_debug("Updated autonomous config [%llu-%llu] for CPU%d\n", 
>> min_perf, max_perf, cpu);
>> +
>> +     return 0;
>> +}
>> +
>>   static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
>>   {
>>       unsigned int cpu = policy->cpu;
>>       struct cppc_cpudata *cpu_data;
>>       struct cppc_perf_caps *caps;
>> +     u64 min_perf, max_perf;
>>       int ret;
>>
>>       cpu_data = cppc_cpufreq_get_cpu_data(cpu);
>> @@ -734,11 +819,31 @@ static int cppc_cpufreq_cpu_init(struct 
>> cpufreq_policy *policy)
>>       policy->cur = cppc_perf_to_khz(caps, caps->highest_perf);
>>       cpu_data->perf_ctrls.desired_perf = caps->highest_perf;
>>
>> -     ret = cppc_set_perf(cpu, &cpu_data->perf_ctrls);
>> -     if (ret) {
>> -             pr_debug("Err setting perf value:%d on CPU:%d. ret:%d\n",
>> -                      caps->highest_perf, cpu, ret);
>> -             goto out;
>> +     if (cpu_data->perf_caps.auto_sel) {
>> +             ret = cppc_set_enable(cpu, true);
> The CPPC enable register is optional.
> However this doesn't mean CPPC is not working.

Ya, changed this in v5.

>> +             if (ret) {
>> +                     pr_err("Failed to enable CPPC on cpu%d (%d)\n", 
>> cpu, ret);
>> +                     goto out;
>> +             }
>> +
>> +             min_perf = cpu_data->perf_ctrls.min_perf ?
>> +                        cpu_data->perf_ctrls.min_perf : 
>> caps->lowest_nonlinear_perf;
>> +             max_perf = cpu_data->perf_ctrls.max_perf ?
>> +                        cpu_data->perf_ctrls.max_perf : 
>> caps->nominal_perf;
>> +
>> +             ret = cppc_cpufreq_update_autosel_config(policy, 
>> min_perf, max_perf, true,
>> + CPPC_EPP_PERFORMANCE_PREF, true, false);
>> +             if (ret) {
>> +                     cppc_set_enable(cpu, false);
>> +                     goto out;
>> +             }
>> +     } else {
>> +             ret = cppc_set_perf(cpu, &cpu_data->perf_ctrls);
>> +             if (ret) {
>> +                     pr_debug("Err setting perf value:%d on CPU:%d. 
>> ret:%d\n",
>> +                              caps->highest_perf, cpu, ret);
>> +                     goto out;
>> +             }
>>       }
>>
>>       cppc_cpufreq_cpu_fie_init(policy);
>> @@ -910,7 +1015,6 @@ static int 
>> cppc_cpufreq_update_auto_select(struct cpufreq_policy *policy, bool e
>>       struct cppc_perf_caps *caps = &cpu_data->perf_caps;
>>       u64 min_perf = caps->lowest_nonlinear_perf;
>>       u64 max_perf = caps->nominal_perf;
>> -     int ret;
>>
>>       if (enable) {
>>               if (cpu_data->perf_ctrls.min_perf)
>> @@ -919,26 +1023,8 @@ static int 
>> cppc_cpufreq_update_auto_select(struct cpufreq_policy *policy, bool e
>>                       max_perf = cpu_data->perf_ctrls.max_perf;
>>       }
>>
>> -     /*
>> -      * Set min/max performance registers and update policy 
>> constraints.
>> -      *   When enabling: update both registers and policy.
>> -      *   When disabling: update policy only.
>> -      * Continue even if min/max are not supported, as EPP and autosel
>> -      * might still be supported.
>> -      */
>> -     ret = cppc_cpufreq_set_min_perf(policy, min_perf, enable, true);
>> -     if (ret && ret != -EOPNOTSUPP)
>> -             return ret;
>> -
>> -     ret = cppc_cpufreq_set_max_perf(policy, max_perf, enable, true);
>> -     if (ret && ret != -EOPNOTSUPP)
>> -             return ret;
>> -
>> -     ret = cppc_cpufreq_update_autosel_val(policy, enable);
>> -     if (ret)
>> -             return ret;
>> -
>> -     return 0;
>> +     return cppc_cpufreq_update_autosel_config(policy, min_perf, 
>> max_perf, enable,
>> +                                               0, false, true);
>>   }
>>
>>   static ssize_t store_auto_select(struct cpufreq_policy *policy, 
>> const char *buf, size_t count)
>> @@ -1146,13 +1232,61 @@ static struct cpufreq_driver 
>> cppc_cpufreq_driver = {
>>       .name = "cppc_cpufreq",
>>   };
>>
>> +static int cppc_cpufreq_set_epp_autosel_allcpus(bool auto_sel, u64 epp)
>> +{
>> +     int cpu, ret;
>> +
>> +     for_each_present_cpu(cpu) {
>> +             ret = cppc_set_epp(cpu, epp);
> Isn't the EPP optional ?

Moving this to cppc_cpufreq_cpu_init in v5. Will add handling for 
EOPNOTSUPP.


> If autonomous selection is available but not EPP, we will bail out.

I couldn't find in spec that EPP is mandatory when auto_select is enabled.


>> +             if (ret) {
>> +                     pr_warn("Failed to set EPP on CPU%d (%d)\n", 
>> cpu, ret);
>> +                     goto disable_all;
>> +             }
>> +
>> +             ret = cppc_set_auto_sel(cpu, auto_sel);
>
> Also, it is possible that a platform only supports autonomous selection.
> In this case, writing to auto_sel will fail, but auto_sel is still 
> relevant.

I am not sure if we will have such platform which only supports Autonomous
mode and has auto_sel as read only. Will add handling for EOPNOTSUPP if we
have such cases as the cppc_get_reg_val() will returns this error.

Thank you,
Sumit Gupta

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