Re: [PATCH v5 11/11] cpufreq: CPPC: add autonomous mode boot parameter support

["zhenglifeng (A)" <zhenglifeng1@huawei.com>]

On 2025/12/23 20:13, Sumit Gupta wrote:
> Add kernel boot parameter 'cppc_cpufreq.auto_sel_mode' to enable CPPC
> autonomous performance selection on all CPUs at system startup without
> requiring runtime sysfs manipulation. When autonomous mode is enabled,
> the hardware automatically adjusts CPU performance based on workload
> demands using Energy Performance Preference (EPP) hints.
> 
> When auto_sel_mode=1:
> - All CPUs are configured for autonomous operation during init
> - EPP is set to performance preference (0x0) by default
> - Min/max performance bounds use defaults or already set values
> - CPU frequency scaling is handled by hardware instead of OS governor
> 
> The boot parameter is applied only during first policy initialization.
> User's runtime sysfs configuration is preserved across hotplug.
> 
> For Documentation/:
> Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
> ---
>  .../admin-guide/kernel-parameters.txt         | 13 +++
>  drivers/cpufreq/cppc_cpufreq.c                | 85 +++++++++++++++++--
>  2 files changed, 90 insertions(+), 8 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index aab72efa1acd..450f0b0225dc 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1035,6 +1035,19 @@ Kernel parameters
>  			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 supported 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 b3da263c18b0..8c6869e68504 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -30,6 +30,9 @@ static struct cpufreq_driver cppc_cpufreq_driver;
>  
>  static DEFINE_MUTEX(cppc_cpufreq_update_autosel_config_lock);
>  
> +/* Autonomous Selection boot parameter */
> +static bool auto_sel_mode;
> +
>  #ifdef CONFIG_ACPI_CPPC_CPUFREQ_FIE
>  static enum {
>  	FIE_UNSET = -1,
> @@ -643,11 +646,16 @@ static int cppc_cpufreq_set_mperf_limit(struct cpufreq_policy *policy, u64 val,
>   * cppc_cpufreq_update_autosel_config - Update autonomous selection config
>   * @policy: cpufreq policy
>   * @is_auto_sel: enable/disable autonomous selection
> + * @epp_val: EPP value (used only if update_epp true)
> + * @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,
> -					      bool is_auto_sel)
> +					      bool is_auto_sel, u32 epp_val,
> +					      bool update_epp,
> +					      bool update_policy)

cppc_cpufreq_set_mperf_limit() and cppc_cpufreq_update_autosel_config()
have too much bool input param. Just break them down into several separate
functions and call them only when needed. These two functions are now too
hard to read.

>  {
>  	struct cppc_cpudata *cpu_data = policy->driver_data;
>  	struct cppc_perf_caps *caps = &cpu_data->perf_caps;
> @@ -655,7 +663,6 @@ static int cppc_cpufreq_update_autosel_config(struct cpufreq_policy *policy,
>  	u64 max_perf = caps->nominal_perf;
>  	unsigned int cpu = policy->cpu;
>  	bool update_reg = is_auto_sel;
> -	bool update_policy = true;
>  	int ret;
>  
>  	guard(mutex)(&cppc_cpufreq_update_autosel_config_lock);
> @@ -685,6 +692,17 @@ static int cppc_cpufreq_update_autosel_config(struct cpufreq_policy *policy,
>  	if (ret && ret != -EOPNOTSUPP)
>  		return ret;
>  
> +	/* Update EPP register */
> +	if (update_epp) {
> +		ret = cppc_set_epp(cpu, epp_val);
> +		if (ret && ret != -EOPNOTSUPP) {
> +			pr_warn("Failed to set EPP for CPU%d (%d)\n", cpu, ret);
> +			return ret;
> +		}
> +		if (!ret)
> +			cpu_data->perf_ctrls.energy_perf = epp_val;
> +	}
> +
>  	/* Update auto_sel register */
>  	ret = cppc_set_auto_sel(cpu, is_auto_sel);
>  	if (ret && ret != -EOPNOTSUPP) {
> @@ -816,11 +834,54 @@ 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;
> +	/*
> +	 * Enable autonomous mode on first init if boot param is set.
> +	 * Check last_governor to detect first init and skip if auto_sel
> +	 * is already enabled.
> +	 */
> +	if (auto_sel_mode && policy->last_governor[0] == '\0' &&
> +	    !cpu_data->perf_ctrls.auto_sel) {
> +		/* Enable CPPC - optional register, some platforms need it */
> +		ret = cppc_set_enable(cpu, true);
> +		if (ret) {
> +			if (ret == -EOPNOTSUPP)
> +				pr_debug("CPPC enable not supported CPU%d\n",
> +					 cpu);
> +			else
> +				pr_warn("Failed enable CPPC CPU%d (%d)\n",
> +					cpu, ret);
> +		}
> +
> +		/*
> +		 * Enable autonomous mode; Pass false for update_policy to avoid
> +		 * updating policy limits prematurely as they are not yet fully setup.
> +		 */
> +		ret = cppc_cpufreq_update_autosel_config(policy,
> +							 true,  /* is_auto_sel */
> +							 CPPC_EPP_PERFORMANCE_PREF,
> +							 true,  /* update_epp */
> +							 false); /* update_policy */
> +		if (ret)
> +			pr_warn("Failed autonomous config CPU%d (%d)\n",
> +				cpu, ret);
> +	}
> +
> +	/* If auto mode is enabled, sync policy limits with HW registers */
> +	if (cpu_data->perf_ctrls.auto_sel) {
> +		policy->min = cppc_perf_to_khz(caps,
> +					       cpu_data->perf_ctrls.min_perf ?:
> +					       caps->lowest_nonlinear_perf);
> +		policy->max = cppc_perf_to_khz(caps,
> +					       cpu_data->perf_ctrls.max_perf ?:
> +					       caps->nominal_perf);
> +	} else {
> +		/* Standard mode: governors control frequency */
> +		ret = cppc_set_perf(cpu, &cpu_data->perf_ctrls);
> +		if (ret) {
> +			pr_debug("Err setting perf value:%d CPU:%d ret:%d\n",
> +				 caps->highest_perf, cpu, ret);
> +			goto out;
> +		}
>  	}
>  
>  	cppc_cpufreq_cpu_fie_init(policy);
> @@ -991,7 +1052,7 @@ static ssize_t store_auto_select(struct cpufreq_policy *policy,
>  	if (ret)
>  		return ret;
>  
> -	ret = cppc_cpufreq_update_autosel_config(policy, val);
> +	ret = cppc_cpufreq_update_autosel_config(policy, val, 0, false, true);
>  	if (ret)
>  		return ret;
>  
> @@ -1253,10 +1314,18 @@ static int __init cppc_cpufreq_init(void)
>  
>  static void __exit cppc_cpufreq_exit(void)
>  {
> +	unsigned int cpu;
> +
> +	for_each_present_cpu(cpu)
> +		cppc_set_auto_sel(cpu, 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");