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Message-ID: <22a86779-102e-48ce-a79e-4a324c554984@arm.com>
Date: Fri, 28 Nov 2025 16:05:42 +0100
From: Pierre Gondois <pierre.gondois@....com>
To: Sumit Gupta <sumitg@...dia.com>
Cc: linux-kernel@...r.kernel.org, corbet@....net,
acpica-devel@...ts.linux.dev, linux-doc@...r.kernel.org,
linux-acpi@...r.kernel.org, linux-pm@...r.kernel.org,
zhanjie9@...ilicon.com, ionela.voinescu@....com, perry.yuan@....com,
mario.limonciello@....com, ray.huang@....com, rdunlap@...radead.org,
zhenglifeng1@...wei.com, robert.moore@...el.com, lenb@...nel.org,
viresh.kumar@...aro.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,
rafael@...nel.org, gautham.shenoy@....com
Subject: Re: [PATCH v4 8/8] cpufreq: CPPC: add autonomous mode boot parameter
support
Hello Sumit,
On 11/28/25 15:29, Sumit Gupta wrote:
>
> 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@...radead.org>
>>> Signed-off-by: Sumit Gupta<sumitg@...dia.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.
I was thinking about the case where the platform:
- supports auto_sel
- doesn't support EPP
Then won't this function return an error code and not set auto_sel even
though
we could have enabled it (without setting the EPP value) ?
>
>
>>> + 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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