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

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

[Sumit Gupta]

Add a kernel boot parameter 'cppc_cpufreq.auto_sel_mode' to enable
CPPC autonomous performance selection on all CPUs at system startup.
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:
- Configure all CPUs for autonomous operation on first init
- Set EPP to performance preference (0x0)
- Use HW min/max_perf when available; otherwise initialize from caps
- Clamp desired_perf to bounds before enabling autonomous mode
- Hardware controls frequency instead of the OS governor

The boot parameter is applied only during first policy initialization.
Skip applying it on CPU hotplug to preserve runtime sysfs configuration.

This patch depends on patch [2] ("cpufreq: Set policy->min and max
as real QoS constraints") so that the policy->min/max set in
cppc_cpufreq_cpu_init() are not overridden by cpufreq_set_policy()
during init.

Reviewed-by: Randy Dunlap <rdunlap@infradead.org> (Documentation)
Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
---
v[1] -> v2:
- Call cppc_set_enable() unconditionally so CPPC is enabled for both
  OS-driven and autonomous modes.
- Init min/max from caps instead of cppc_cpufreq_update_perf_limits()
  as policy->min/max aren't yet populated.

[1] https://lore.kernel.org/lkml/20260317151053.2361475-1-sumitg@nvidia.com/
[2] https://lore.kernel.org/lkml/20260423084731.1090384-2-pierre.gondois@arm.com/
---
 .../admin-guide/kernel-parameters.txt         | 13 +++
 drivers/cpufreq/cppc_cpufreq.c                | 89 +++++++++++++++++--
 2 files changed, 97 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 0a1abed1b93c..751817b0573a 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1067,6 +1067,19 @@ Kernel parameters
 			policy to use. This governor must be registered in the
 			kernel before the cpufreq driver probes.
 
+	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
+
 	cpu_init_udelay=N
 			[X86,EARLY] Delay for N microsec between assert and de-assert
 			of APIC INIT to start processors.  This delay occurs
diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 02db03d03755..672fc3058190 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -28,6 +28,9 @@
 
 static struct cpufreq_driver cppc_cpufreq_driver;
 
+/* Autonomous Selection boot parameter */
+static bool auto_sel_mode;
+
 #ifdef CONFIG_ACPI_CPPC_CPUFREQ_FIE
 static enum {
 	FIE_UNSET = -1,
@@ -656,6 +659,14 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
 	caps = &cpu_data->perf_caps;
 	policy->driver_data = cpu_data;
 
+	/*
+	 * Enable CPPC for both OS-driven and autonomous modes.
+	 * The Enable register is optional - some platforms may not support it
+	 */
+	ret = cppc_set_enable(cpu, true);
+	if (ret && ret != -EOPNOTSUPP)
+		pr_warn("Failed to enable CPPC for CPU%d (%d)\n", cpu, ret);
+
 	min = cppc_perf_to_khz(caps, caps->lowest_nonlinear_perf);
 	max = cppc_perf_to_khz(caps, policy->boost_enabled ?
 			caps->highest_perf : caps->nominal_perf);
@@ -711,11 +722,71 @@ 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) {
+		/* Init min/max_perf from caps if not already set by HW. */
+		if (!cpu_data->perf_ctrls.min_perf)
+			cpu_data->perf_ctrls.min_perf = caps->lowest_nonlinear_perf;
+		if (!cpu_data->perf_ctrls.max_perf)
+			cpu_data->perf_ctrls.max_perf = policy->boost_enabled ?
+				caps->highest_perf : caps->nominal_perf;
+
+		cpu_data->perf_ctrls.desired_perf =
+			clamp_t(u32, cpu_data->perf_ctrls.desired_perf,
+				cpu_data->perf_ctrls.min_perf,
+				cpu_data->perf_ctrls.max_perf);
+
+		policy->cur = cppc_perf_to_khz(caps,
+					       cpu_data->perf_ctrls.desired_perf);
+
+		/* EPP is optional - some platforms may not support it */
+		ret = cppc_set_epp(cpu, CPPC_EPP_PERFORMANCE_PREF);
+		if (ret && ret != -EOPNOTSUPP)
+			pr_warn("Failed to set EPP for CPU%d (%d)\n", cpu, ret);
+		else if (!ret)
+			cpu_data->perf_ctrls.energy_perf = CPPC_EPP_PERFORMANCE_PREF;
+
+		/* Program min/max/desired into CPPC regs before enabling auto_sel. */
+		ret = cppc_set_perf(cpu, &cpu_data->perf_ctrls);
+		if (ret) {
+			pr_debug("Err setting perf for autonomous mode CPU:%d ret:%d\n",
+				 cpu, ret);
+			goto out;
+		}
+
+		ret = cppc_set_auto_sel(cpu, true);
+		if (ret && ret != -EOPNOTSUPP) {
+			pr_warn("Failed autonomous config for CPU%d (%d)\n",
+				cpu, ret);
+			goto out;
+		}
+		if (!ret)
+			cpu_data->perf_ctrls.auto_sel = true;
+	}
+
+	if (cpu_data->perf_ctrls.auto_sel) {
+		/* Sync policy limits from HW when autonomous mode is active */
+		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 ?:
+					       (policy->boost_enabled ?
+						caps->highest_perf :
+						caps->nominal_perf));
+	} else {
+		/* Normal mode: governors control frequency */
+		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);
@@ -1035,10 +1106,18 @@ 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, 0444);
+MODULE_PARM_DESC(auto_sel_mode, "Enable CPPC autonomous performance selection at boot");
+
 module_exit(cppc_cpufreq_exit);
 MODULE_AUTHOR("Ashwin Chaugule");
 MODULE_DESCRIPTION("CPUFreq driver based on the ACPI CPPC v5.0+ spec");
-- 
2.34.1

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

[Jie Zhan]

Hi Sumit,

In general, I would expect this parameter only toggles on auto_sel by
default.  IIUC, other CPPC configurations (min/max/desired perf, EPP,
enable) are optional and not closely related to this.

Why including those stuff here?


Please see other questions inline.

Thanks!
Jie

On 4/25/2026 4:18 AM, Sumit Gupta wrote:
> Add a kernel boot parameter 'cppc_cpufreq.auto_sel_mode' to enable
> CPPC autonomous performance selection on all CPUs at system startup.
> 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:
> - Configure all CPUs for autonomous operation on first init
> - Set EPP to performance preference (0x0)
> - Use HW min/max_perf when available; otherwise initialize from caps
> - Clamp desired_perf to bounds before enabling autonomous mode
> - Hardware controls frequency instead of the OS governor
> 
> The boot parameter is applied only during first policy initialization.
> Skip applying it on CPU hotplug to preserve runtime sysfs configuration.
> 
> This patch depends on patch [2] ("cpufreq: Set policy->min and max
> as real QoS constraints") so that the policy->min/max set in
> cppc_cpufreq_cpu_init() are not overridden by cpufreq_set_policy()
> during init.
> 
> Reviewed-by: Randy Dunlap <rdunlap@infradead.org> (Documentation)
> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
> ---
> v[1] -> v2:
> - Call cppc_set_enable() unconditionally so CPPC is enabled for both
>   OS-driven and autonomous modes.
Why adding this in v2?
This looks like a separate issue since setting CPPC Enable reg doesn't seem
to be related with autonomous control.
> - Init min/max from caps instead of cppc_cpufreq_update_perf_limits()
>   as policy->min/max aren't yet populated.
> 
> [1] https://lore.kernel.org/lkml/20260317151053.2361475-1-sumitg@nvidia.com/
> [2] https://lore.kernel.org/lkml/20260423084731.1090384-2-pierre.gondois@arm.com/
> ---
>  .../admin-guide/kernel-parameters.txt         | 13 +++
>  drivers/cpufreq/cppc_cpufreq.c                | 89 +++++++++++++++++--
>  2 files changed, 97 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 0a1abed1b93c..751817b0573a 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1067,6 +1067,19 @@ Kernel parameters
>  			policy to use. This governor must be registered in the
>  			kernel before the cpufreq driver probes.
>  
> +	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
> +
>  	cpu_init_udelay=N
>  			[X86,EARLY] Delay for N microsec between assert and de-assert
>  			of APIC INIT to start processors.  This delay occurs
> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> index 02db03d03755..672fc3058190 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -28,6 +28,9 @@
>  
>  static struct cpufreq_driver cppc_cpufreq_driver;
>  
> +/* Autonomous Selection boot parameter */
> +static bool auto_sel_mode;
> +
>  #ifdef CONFIG_ACPI_CPPC_CPUFREQ_FIE
>  static enum {
>  	FIE_UNSET = -1,
> @@ -656,6 +659,14 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
>  	caps = &cpu_data->perf_caps;
>  	policy->driver_data = cpu_data;
>  
> +	/*
> +	 * Enable CPPC for both OS-driven and autonomous modes.
> +	 * The Enable register is optional - some platforms may not support it
> +	 */
> +	ret = cppc_set_enable(cpu, true);
> +	if (ret && ret != -EOPNOTSUPP)
> +		pr_warn("Failed to enable CPPC for CPU%d (%d)\n", cpu, ret);
> +
>  	min = cppc_perf_to_khz(caps, caps->lowest_nonlinear_perf);
>  	max = cppc_perf_to_khz(caps, policy->boost_enabled ?
>  			caps->highest_perf : caps->nominal_perf);
> @@ -711,11 +722,71 @@ 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) {
> +		/* Init min/max_perf from caps if not already set by HW. */
> +		if (!cpu_data->perf_ctrls.min_perf)
> +			cpu_data->perf_ctrls.min_perf = caps->lowest_nonlinear_perf;
> +		if (!cpu_data->perf_ctrls.max_perf)
> +			cpu_data->perf_ctrls.max_perf = policy->boost_enabled ?
> +				caps->highest_perf : caps->nominal_perf;
Is it automatically adjusted when switching boost on and off?
> +
> +		cpu_data->perf_ctrls.desired_perf =
> +			clamp_t(u32, cpu_data->perf_ctrls.desired_perf,
> +				cpu_data->perf_ctrls.min_perf,
> +				cpu_data->perf_ctrls.max_perf);
Why do we need to clamp desire_perf here?
> +
> +		policy->cur = cppc_perf_to_khz(caps,
> +					       cpu_data->perf_ctrls.desired_perf);
> +
> +		/* EPP is optional - some platforms may not support it */
> +		ret = cppc_set_epp(cpu, CPPC_EPP_PERFORMANCE_PREF);
Why setting this to PERFORMANCE by default?
A platform can have its own default EPP value.  This would override that.
> +		if (ret && ret != -EOPNOTSUPP)
> +			pr_warn("Failed to set EPP for CPU%d (%d)\n", cpu, ret);
> +		else if (!ret)
> +			cpu_data->perf_ctrls.energy_perf = CPPC_EPP_PERFORMANCE_PREF;
> +
> +		/* Program min/max/desired into CPPC regs before enabling auto_sel. */
> +		ret = cppc_set_perf(cpu, &cpu_data->perf_ctrls);
> +		if (ret) {
> +			pr_debug("Err setting perf for autonomous mode CPU:%d ret:%d\n",
> +				 cpu, ret);
> +			goto out;
Shouldn't this be pr_warn(), or even pr_err(), if it needs to bail out?

However, IIUC setting min/max/desired perf is optional for auto_sel, so
better to pr_info() and continue setting auto_sel?
> +		}
> +
> +		ret = cppc_set_auto_sel(cpu, true);
> +		if (ret && ret != -EOPNOTSUPP) {
> +			pr_warn("Failed autonomous config for CPU%d (%d)\n",
> +				cpu, ret);
> +			goto out;
Bailing out here would end up without DVFS support.
Can we fall back to the normal OS directed mode?
> +		}
> +		if (!ret)
> +			cpu_data->perf_ctrls.auto_sel = true;
> +	}
> +
> +	if (cpu_data->perf_ctrls.auto_sel) {
> +		/* Sync policy limits from HW when autonomous mode is active */
> +		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 ?:
> +					       (policy->boost_enabled ?
> +						caps->highest_perf :
> +						caps->nominal_perf));
> +	} else {
> +		/* Normal mode: governors control frequency */
> +		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);
> @@ -1035,10 +1106,18 @@ 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, 0444);
> +MODULE_PARM_DESC(auto_sel_mode, "Enable CPPC autonomous performance selection at boot");
> +
>  module_exit(cppc_cpufreq_exit);
>  MODULE_AUTHOR("Ashwin Chaugule");
>  MODULE_DESCRIPTION("CPUFreq driver based on the ACPI CPPC v5.0+ spec");