Re: [PATCH v2 7/7] cpufreq: CPPC: add autonomous mode boot parameter support

[Mario Limonciello <mario.limonciello@amd.com>]

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@nvidia.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".

> +
>   	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)();

> +
> +	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.

> +	}
> +	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.

> +
>   module_exit(cppc_cpufreq_exit);
>   MODULE_AUTHOR("Ashwin Chaugule");
>   MODULE_DESCRIPTION("CPUFreq driver based on the ACPI CPPC v5.0+ spec");