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

Sumit Gupta
2025-12-23T12:16:53Z

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)
{
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");
--
2.34.1