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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 >> Signed-off-by: Sumit Gupta >> --- >> .../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: >> ,,,[,] >> >> + 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: >> + 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 >> >> 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 >>