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Message-ID: <cba8314f-7e01-464b-9ba2-e337395a453b@nvidia.com>
Date: Mon, 1 Dec 2025 19:39:45 +0530
From: Sumit Gupta <sumitg@...dia.com>
To: Pierre Gondois <pierre.gondois@....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, sumitg@...dia.com
Subject: Re: [PATCH v4 8/8] cpufreq: CPPC: add autonomous mode boot parameter
support
>>>
>>>
>>> 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) ?
>
Ya, right. For that will handle EOPNOTSUPP after reading EPP.
Thank you,
Sumit Gupta
>
>>
>>
>>>> + 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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