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

zhenglifeng (A)
2025-12-26T08:03:47Z

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");