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Message-ID: <5593d364-ca37-41c5-b33f-f7e245d6d626@nvidia.com>
Date: Wed, 26 Nov 2025 19:02:05 +0530
From: Sumit Gupta <sumitg@...dia.com>
To: Ionela Voinescu <ionela.voinescu@....com>
Cc: rafael@...nel.org, viresh.kumar@...aro.org, lenb@...nel.org,
robert.moore@...el.com, corbet@....net, pierre.gondois@....com,
zhenglifeng1@...wei.com, rdunlap@...radead.org, ray.huang@....com,
gautham.shenoy@....com, mario.limonciello@....com, perry.yuan@....com,
zhanjie9@...ilicon.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,
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, sumitg@...dia.com
Subject: Re: [PATCH v4 8/8] cpufreq: CPPC: add autonomous mode boot parameter
support
On 13/11/25 20:45, Ionela Voinescu wrote:
> External email: Use caution opening links or attachments
>
>
> Hi,
>
> As an overall comment, there are now various functions that modify the
> autonomous selection configuration in various degrees:
> cppc_cpufreq_update_autosel_config, cppc_cpufreq_update_auto_select,
> cppc_cpufreq_set_epp_autosel_allcpus.
>
> Are these all really necessary? Some seem single use functions that
> make the intention very confusing through the use of several bool
> parameters. I think a lot of this complexity can be avoided, so
> I'd recommend to re-think the software design a bit.
>
> I've added more details below (and I've skipped review of the previous
> patch).
Sure, will do the changes in v5.
> On Wednesday 05 Nov 2025 at 17:08:44 (+0530), 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);
> "When Autonomous Selection is enabled, it is not necessary for OSPM to assess
> processor workload performance demand and convey a corresponding performance
> delivery request to the platform via the Desired Register. If the Desired
> Performance Register exists, OSPM may provide an explicit performance
> requirement hint to the platform by writing a non-zero value."
>
> Therefore I believe it's up to the platform to decide if it wants to use
> the software hint.
Ok, will remove the check in v5.
>> 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;
>> + }
>> +
> This belongs to patch 2/8.
will move in v5.
>
>> 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, epp curr:%u, new:%u\n", cpu, cpu_data->perf_ctrls.energy_perf, epp);
>> +
>> + guard(mutex)(&cppc_cpufreq_update_autosel_config_lock);
>> +
>> + ret = cppc_set_epp(cpu, epp);
>> + if (ret) {
>> + pr_warn("failed to set energy_perf for cpu:%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;
>> +}
> I think cppc_cpufreq_update_auto_select() can be removed and
> cppc_cpufreq_update_autosel_config() used in its place.
>
> cppc_cpufreq_update_autosel_config() would not even need min/max as
> arguments as they can be obtained from perf_caps (low/nominal range)
> or perf_ctrls (current min/max). This would also simplify
> cppc_cpufreq_cpu_init().
Will change in v5.
>> +
>> 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);
> Isn't auto-sel enabled at this point? Also, if the auto-sel is
> ACPI_TYPE_INTEGER, cppc_set_enable() will return an error,
> isn't it?
Do you mean CPPC enable rather than auto-sel?
Some platforms may require the Kernel to explicitly set the CPPC Enable
register which is of type ACPI_TYPE_BUFFER. I will add error handling for
cases where this register is not supported, not visible, or is read-only of
ACPI_TYPE_INTEGER to the Kernel.
>> + if (ret) {
>> + pr_err("Failed to enable CPPC on cpu%d (%d)\n", cpu, ret);
>> + goto out;
> Do you really want to bail out of the rest of the cpufreq CPU
> initialisation, if only auto-select configuration fails?
Will do the change in v5.
>> + }
>> +
>> + 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);
>> + 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);
>> + if (ret) {
>> + pr_warn("Failed to set auto_sel on CPU%d (%d)\n", cpu, ret);
>> + goto disable_all;
>> + }
>> + }
>> +
>> + return 0;
>> +
>> +disable_all:
>> + pr_warn("Disabling auto_sel for all CPUs\n");
>> + for_each_present_cpu(cpu)
>> + cppc_set_auto_sel(cpu, false);
>> +
>> + return -EIO;
>> +}
>> +
>> static int __init cppc_cpufreq_init(void)
>> {
>> + bool auto_sel;
>> int ret;
>>
>> if (!acpi_cpc_valid())
>> return -ENODEV;
>>
>> + if (auto_sel_mode) {
>> + /*
>> + * Check if autonomous selection is supported by testing CPU 0.
>> + * If supported, enable autonomous mode on all CPUs.
>> + */
>> + ret = cppc_get_auto_sel(0, &auto_sel);
>> + if (!ret) {
>> + pr_info("Enabling auto_sel_mode (autonomous selection mode)\n");
>> + ret = cppc_cpufreq_set_epp_autosel_allcpus(true, CPPC_EPP_PERFORMANCE_PREF);
>> + if (ret) {
>> + pr_warn("Disabling auto_sel_mode, fallback to standard\n");
>> + auto_sel_mode = false;
>> + }
>> + } else {
>> + pr_warn("Disabling auto_sel_mode as not supported by hardware\n");
>> + auto_sel_mode = false;
>> + }
>> + }
>> +
> Why not check at cppc_cpufreq_cpu_init? In the unlikely case that one
> CPU does not support it, I would recommend to issue a warning, rather
> than disable auto-sel on all the other CPUs. It is possible that some
> CPUs support auto-sel and they have it enabled by default without
> exposing that control to the OS.
Will move to cppc_cpufreq_cpu_init in v5.
Thank you,
Sumit Gupta
>> cppc_freq_invariance_init();
>> populate_efficiency_class();
>>
>> @@ -1165,10 +1299,19 @@ static int __init cppc_cpufreq_init(void)
>>
>> static void __exit cppc_cpufreq_exit(void)
>> {
>> + int cpu;
>> +
>> + for_each_present_cpu(cpu)
>> + cppc_set_auto_sel(cpu, false);
>> + auto_sel_mode = false;
>> +
>> cpufreq_unregister_driver(&cppc_cpufreq_driver);
>> cppc_freq_invariance_exit();
>> }
>>
>> +module_param(auto_sel_mode, bool, 0000);
>> +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");
>> --
>> 2.34.1
>>
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