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Message-ID: <30b46202-d377-4455-9551-5874e1e9f104@nvidia.com>
Date: Mon, 1 Sep 2025 19:07:00 +0530
From: Sumit Gupta <sumitg@...dia.com>
To: Mario Limonciello <mario.limonciello@....com>, rafael@...nel.org,
viresh.kumar@...aro.org, lenb@...nel.org, robert.moore@...el.com,
corbet@....net, pierre.gondois@....com, zhenglifeng1@...wei.com,
ray.huang@....com, gautham.shenoy@....com, perry.yuan@....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
Cc: linux-tegra@...r.kernel.org, treding@...dia.com, jonathanh@...dia.com,
vsethi@...dia.com, ksitaraman@...dia.com, sanjayc@...dia.com,
bbasu@...dia.com, sumitg@...dia.com
Subject: Re: [PATCH v2 7/7] cpufreq: CPPC: add autonomous mode boot parameter
support
On 26/08/25 00:10, Mario Limonciello wrote:
> External email: Use caution opening links or attachments
>
>
> On 8/23/2025 3:01 PM, 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 from
>> the OS.
>>
>> 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 driver init
>> - EPP is set to performance preference (0x0) by default
>> - Min/max performance bounds use defaults
>> - CPU frequency scaling is handled by hardware rather than OS
>>
>> Also ensure that when autonomous mode is active, the set_target callback
>> returns early since hardware controls frequency scaling directly.
>>
>> Signed-off-by: Sumit Gupta <sumitg@...dia.com>
>> ---
>> .../admin-guide/kernel-parameters.txt | 12 ++
>> drivers/cpufreq/cppc_cpufreq.c | 171 ++++++++++++++++--
>> 2 files changed, 168 insertions(+), 15 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt
>> b/Documentation/admin-guide/kernel-parameters.txt
>> index 86f395f2933b..ea58deb88c36 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -911,6 +911,18 @@
>> Format:
>> <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
>>
>> + cppc_cpufreq.auto_sel_mode=
>> + [CPU_FREQ] Autonomous Performance Level Selection.
>> + When Autonomous selection is enabled, then the
>> hardware is
>> + allowed to autonomously select the CPU frequency.
>> + In Autonomous mode, Energy Performance
>> Preference(EPP)
>> + provides input to the hardware to favour
>> performance (0x0)
>> + or energy efficiency (0xff).
>> + Format: <bool>
>> + Default: disabled.
>> + 0: force disabled
>> + 1: force enabled
>
> I don't think you can actually force enable. If the hardware doesn't
> support it, setting 1 won't do anything.
>
> IoW really setting 1 is "enable if supported".
>
Yes, will change in v3.
>> +
>> 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 5e1bbb5f67b8..bbf654c56ff9 100644
>> --- a/drivers/cpufreq/cppc_cpufreq.c
>> +++ b/drivers/cpufreq/cppc_cpufreq.c
>> @@ -27,6 +27,8 @@
>> #include <acpi/cppc_acpi.h>
>>
>> static struct cpufreq_driver cppc_cpufreq_driver;
>> +/* Autonomous Selection */
>> +static bool auto_sel_mode;
>>
>> #ifdef CONFIG_ACPI_CPPC_CPUFREQ_FIE
>> static enum {
>> @@ -272,6 +274,14 @@ static int cppc_cpufreq_set_target(struct
>> cpufreq_policy *policy,
>> freqs.old = policy->cur;
>> freqs.new = target_freq;
>>
>> + /*
>> + * In autonomous mode, hardware handles frequency scaling directly
>> + * based on workload demands and EPP hints, so OS frequency
>> requests
>> + * are not needed.
>> + */
>> + if (cpu_data->perf_caps.auto_sel)
>> + return ret;
>> +
>> cpufreq_freq_transition_begin(policy, &freqs);
>> ret = cppc_set_perf_ctrls(cpu, &cpu_data->perf_ctrls);
>> cpufreq_freq_transition_end(policy, &freqs, ret != 0);
>> @@ -555,6 +565,12 @@ static struct cppc_cpudata
>> *cppc_cpufreq_get_cpu_data(unsigned int cpu)
>> goto free_mask;
>> }
>>
>> + ret = cppc_get_perf_ctrls(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:
>> @@ -642,6 +658,79 @@ static int cppc_cpufreq_set_max_perf(struct
>> cpufreq_policy *policy, u64 val,
>> return (ret == -EOPNOTSUPP) ? 0 : ret;
>> }
>>
>> +static int cppc_cpufreq_update_autosel_epp(struct cpufreq_policy
>> *policy, int auto_sel, u32 epp)
>> +{
>> + struct cppc_cpudata *cpu_data = policy->driver_data;
>> + unsigned int cpu = policy->cpu;
>> + int ret;
>> +
>> + pr_debug("cpu%d: curr epp:%u, curr mode:%u, new epp:%u, new
>> mode:%d\n", cpu,
>> + cpu_data->perf_ctrls.energy_perf,
>> cpu_data->perf_caps.auto_sel, epp, auto_sel);
>> +
>> + mutex_lock(&cppc_cpufreq_update_autosel_config_lock);
>
> As I noticed below a case you missed the mutex unlock, this feels like a
> good candidate for
>
> guard(mutex)();
>
I will check about 'guard(mutex)()' and change accordingly in v3.
>> +
>> + ret = cppc_set_epp(cpu, epp);
>> + if (ret) {
>> + pr_warn("failed to set energy_perf for cpu:%d (%d)\n",
>> cpu, ret);
>> + goto out;
>> + }
>> + cpu_data->perf_ctrls.energy_perf = epp;
>> +
>> + ret = cppc_set_auto_sel(cpu, auto_sel);
>> + if (ret) {
>> + pr_warn("failed to set auto_sel for cpu:%d (%d)\n",
>> cpu, ret);
>> + return ret;
>
> Looks like a case that you didn't unlock the mutex.
ACK.
>
>> + }
>> + cpu_data->perf_caps.auto_sel = auto_sel;
>> +
>> +out:
>> + mutex_unlock(&cppc_cpufreq_update_autosel_config_lock);
>> + return ret;
>> +}
>> +
>> +static int cppc_cpufreq_update_autosel_mperf_ctrls(struct
>> cpufreq_policy *policy, u32 min_p,
>> + u32 max_p, bool
>> update_reg, bool update_policy)
>> +{
>> + struct cppc_cpudata *cpu_data = policy->driver_data;
>> + unsigned int cpu = policy->cpu;
>> + int ret;
>> +
>> + pr_debug("cpu%d: curr max_perf:%u, curr min_perf:%u, new
>> max_perf:%u, new min_perf:%u\n",
>> + cpu, cpu_data->perf_ctrls.max_perf,
>> cpu_data->perf_ctrls.min_perf, max_p, min_p);
>> +
>> + ret = cppc_cpufreq_set_min_perf(policy, min_p, update_reg,
>> update_policy);
>> + if (ret) {
>> + pr_debug("failed to set min_perf for cpu:%d (%d)\n",
>> cpu, ret);
>> + return ret;
>> + }
>> +
>> + ret = cppc_cpufreq_set_max_perf(policy, max_p, update_reg,
>> update_policy);
>> + if (ret) {
>> + pr_debug("failed to set max_perf for cpu:%d (%d)\n",
>> cpu, ret);
>> + return ret;
>> + }
>> +
>> + return ret;
>> +}
>> +
>> +static int cppc_cpufreq_update_autosel_configs(struct cpufreq_policy
>> *policy, int auto_sel,
>> + u32 epp, u32 min_perf,
>> u32 max_perf,
>> + bool update_reg, bool
>> update_policy)
>> +{
>> + int ret;
>> +
>> + ret = cppc_cpufreq_update_autosel_mperf_ctrls(policy, min_perf,
>> max_perf,
>> + update_reg,
>> update_policy);
>> + if (ret)
>> + return ret;
>> +
>> + ret = cppc_cpufreq_update_autosel_epp(policy, auto_sel, epp);
>> + if (ret)
>> + return ret;
>> +
>> + return 0;
>> +}
>> +
>> static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
>> {
>> unsigned int cpu = policy->cpu;
>> @@ -710,11 +799,28 @@ 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_ctrls(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);
>> + if (ret) {
>> + pr_err("Failed to enable CPPC on cpu%d (%d)\n",
>> cpu, ret);
>> + goto out;
>> + }
>> +
>> + ret = cppc_cpufreq_update_autosel_configs(policy, true,
>> + CPPC_EPP_PERFORMANCE_PREF,
>> + caps->lowest_nonlinear_perf,
>> + caps->nominal_perf, true, false);
>> + if (ret) {
>> + pr_debug("Failed to update autosel configs on
>> CPU%d(%d)\n", cpu, ret);
>> + goto out;
>> + }
>> + } else {
>> + ret = cppc_set_perf_ctrls(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);
>> @@ -736,6 +842,13 @@ static void cppc_cpufreq_cpu_exit(struct
>> cpufreq_policy *policy)
>>
>> cpu_data->perf_ctrls.desired_perf = caps->lowest_perf;
>>
>> + if (cpu_data->perf_caps.auto_sel) {
>> + ret = cppc_cpufreq_update_autosel_epp(policy, false,
>> + CPPC_EPP_ENERGY_EFFICIENCY_PREF);
>> + if (ret)
>> + return;
>> + }
>> +
>> ret = cppc_set_perf_ctrls(cpu, &cpu_data->perf_ctrls);
>> if (ret)
>> pr_debug("Err setting perf value:%d on CPU:%d. ret:%d\n",
>> @@ -920,17 +1033,10 @@ static ssize_t store_auto_select(struct
>> cpufreq_policy *policy,
>> * On enabling auto_select: set min/max_perf register and
>> update policy.
>> * On disabling auto_select: update only policy.
>> */
>> - ret = cppc_cpufreq_set_min_perf(policy, min_perf, update_reg,
>> true);
>> - if (ret) {
>> - pr_warn("failed to %s update min policy for cpu:%d
>> (%d)\n",
>> - val > 0 ? "set min_perf and" : "", cpu, ret);
>> - return ret;
>> - }
>> -
>> - ret = cppc_cpufreq_set_max_perf(policy, max_perf, update_reg,
>> true);
>> + ret = cppc_cpufreq_update_autosel_mperf_ctrls(policy, min_perf,
>> max_perf, update_reg, true);
>> if (ret) {
>> - pr_warn("failed to %s update max policy for cpu:%d
>> (%d)\n",
>> - val > 0 ? "set max_perf and" : "", cpu, ret);
>> + pr_warn("failed to %s update policy for cpu:%d (%d)\n",
>> + val > 0 ? "set min/max_perf and" : "", cpu, ret);
>> return ret;
>> }
>>
>> @@ -1139,13 +1245,44 @@ static struct cpufreq_driver
>> cppc_cpufreq_driver = {
>> .name = "cppc_cpufreq",
>> };
>>
>> +static void 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_debug("failed to set energy_perf for cpu:%d
>> (%d)\n", cpu, ret);
>> +
>> + ret = cppc_set_auto_sel(cpu, auto_sel);
>> + if (ret)
>> + pr_debug("failed to set auto_sel for cpu:%d
>> (%d)\n", cpu, ret);
>> + }
>> +}
>> +
>> 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 autonomous mode on all CPUs\n");
>> + cppc_cpufreq_set_epp_autosel_allcpus(true,
>> CPPC_EPP_PERFORMANCE_PREF);
>> + } else {
>> + pr_warn("Autonomous selection not supported,
>> disabling auto_sel_mode\n");
>> + auto_sel_mode = false;
>> + }
>> + }
>> +
>> cppc_freq_invariance_init();
>> populate_efficiency_class();
>>
>> @@ -1160,8 +1297,12 @@ static void __exit cppc_cpufreq_exit(void)
>> {
>> cpufreq_unregister_driver(&cppc_cpufreq_driver);
>> cppc_freq_invariance_exit();
>> + auto_sel_mode = 0;
>> }
>>
>> +module_param(auto_sel_mode, bool, 0000);
>> +MODULE_PARM_DESC(auto_sel_mode, "Enable Autonomous Performance Level
>> Selection");
>
> Why default to disabled? As a precaution? We enable EPP by default in
> the *-pstate drivers if the hardware supports it, I would think it makes
> sense here too.
>
Kept disabled by default both as precaution and to enable it based on
preference.
Someone may want to try different config values during bringup,
verification etc.
Thank you,
Sumit Gupta
>> +
>> module_exit(cppc_cpufreq_exit);
>> MODULE_AUTHOR("Ashwin Chaugule");
>> MODULE_DESCRIPTION("CPUFreq driver based on the ACPI CPPC v5.0+
>> spec");
>
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