[PATCH v2] arm64: topology: Setup AMU FIE for online CPUs only

[PATCH v2] arm64: topology: Setup AMU FIE for online CPUs only

[Lifeng Zheng]

When boot with maxcpu=1 restrict, and LPI(Low Power Idle States) is on,
only CPU0 will go online. The support AMU flag of CPU0 will be set but the
flags of other CPUs will not. This will cause AMU FIE set up fail for CPU0
when it shares a cpufreq policy with other CPU(s). After that, when other
CPUs are finally online and the support AMU flags of them are set, they'll
never have a chance to set up AMU FIE, even though they're eligible.

To solve this problem, the process of setting up AMU FIE needs to be
modified as follows:

1. Set up AMU FIE only for the online CPUs.

2. Try to set up AMU FIE each time a CPU goes online and do the
freq_counters_valid() check for all the online CPUs share the same policy.
If this check fails, clear scale freq source of these CPUs, in case they
use different source of the freq scale.

Signed-off-by: Lifeng Zheng <zhenglifeng1@huawei.com>
---
 arch/arm64/kernel/topology.c | 49 ++++++++++++++++++++++++++++++++----
 1 file changed, 44 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 5d07ee85bdae..d578c496d457 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -357,12 +357,15 @@ static void amu_fie_setup(const struct cpumask *cpus)
 
 	/* We are already set since the last insmod of cpufreq driver */
 	if (cpumask_available(amu_fie_cpus) &&
-	    unlikely(cpumask_subset(cpus, amu_fie_cpus)))
+	    cpumask_subset(cpus, amu_fie_cpus))
 		return;
 
-	for_each_cpu(cpu, cpus)
-		if (!freq_counters_valid(cpu))
+	for_each_cpu(cpu, cpus) {
+		if (!freq_counters_valid(cpu)) {
+			topology_clear_scale_freq_source(SCALE_FREQ_SOURCE_ARCH, cpus);
 			return;
+		}
+	}
 
 	if (!cpumask_available(amu_fie_cpus) &&
 	    !zalloc_cpumask_var(&amu_fie_cpus, GFP_KERNEL)) {
@@ -385,7 +388,7 @@ static int init_amu_fie_callback(struct notifier_block *nb, unsigned long val,
 	struct cpufreq_policy *policy = data;
 
 	if (val == CPUFREQ_CREATE_POLICY)
-		amu_fie_setup(policy->related_cpus);
+		amu_fie_setup(policy->cpus);
 
 	/*
 	 * We don't need to handle CPUFREQ_REMOVE_POLICY event as the AMU
@@ -404,10 +407,46 @@ static struct notifier_block init_amu_fie_notifier = {
 	.notifier_call = init_amu_fie_callback,
 };
 
+static int cpuhp_topology_online(unsigned int cpu)
+{
+	struct cpufreq_policy *policy __free(put_cpufreq_policy);
+	cpumask_var_t cpus_to_set;
+
+	if (!zalloc_cpumask_var(&cpus_to_set, GFP_KERNEL))
+		return -ENOMEM;
+
+	cpumask_copy(cpus_to_set, cpumask_of(cpu));
+
+	policy = cpufreq_cpu_get(cpu);
+	if (policy) {
+		cpumask_or(cpus_to_set, cpus_to_set, policy->cpus);
+		amu_fie_setup(cpus_to_set);
+	}
+
+	free_cpumask_var(cpus_to_set);
+	return 0;
+}
+
 static int __init init_amu_fie(void)
 {
-	return cpufreq_register_notifier(&init_amu_fie_notifier,
+	int ret;
+
+	ret = cpufreq_register_notifier(&init_amu_fie_notifier,
 					CPUFREQ_POLICY_NOTIFIER);
+	if (ret)
+		return ret;
+
+	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
+					"arm64/topology:online",
+					cpuhp_topology_online,
+					NULL);
+	if (ret < 0) {
+		cpufreq_unregister_notifier(&init_amu_fie_notifier,
+					    CPUFREQ_POLICY_NOTIFIER);
+		return ret;
+	}
+
+	return 0;
 }
 core_initcall(init_amu_fie);
 
-- 
2.33.0

Re: [PATCH v2] arm64: topology: Setup AMU FIE for online CPUs only

[Sudeep Holla]

On Fri, Jul 25, 2025 at 06:28:13PM +0800, Lifeng Zheng wrote:
> When boot with maxcpu=1 restrict, and LPI(Low Power Idle States) is on,
> only CPU0 will go online. The support AMU flag of CPU0 will be set but the
> flags of other CPUs will not. This will cause AMU FIE set up fail for CPU0
> when it shares a cpufreq policy with other CPU(s). After that, when other
> CPUs are finally online and the support AMU flags of them are set, they'll
> never have a chance to set up AMU FIE, even though they're eligible.
> 
> To solve this problem, the process of setting up AMU FIE needs to be
> modified as follows:
> 
> 1. Set up AMU FIE only for the online CPUs.
> 
> 2. Try to set up AMU FIE each time a CPU goes online and do the
> freq_counters_valid() check for all the online CPUs share the same policy.
> If this check fails, clear scale freq source of these CPUs, in case they
> use different source of the freq scale.
> 
> Signed-off-by: Lifeng Zheng <zhenglifeng1@huawei.com>
> ---

I have no idea what changed from v1->v2 and no link to v1 for me to
refer to it and check the delta 🙁.

>  arch/arm64/kernel/topology.c | 49 ++++++++++++++++++++++++++++++++----
>  1 file changed, 44 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> index 5d07ee85bdae..d578c496d457 100644
> --- a/arch/arm64/kernel/topology.c
> +++ b/arch/arm64/kernel/topology.c
> @@ -357,12 +357,15 @@ static void amu_fie_setup(const struct cpumask *cpus)
>  
>  	/* We are already set since the last insmod of cpufreq driver */
>  	if (cpumask_available(amu_fie_cpus) &&
> -	    unlikely(cpumask_subset(cpus, amu_fie_cpus)))
> +	    cpumask_subset(cpus, amu_fie_cpus))
>  		return;
>  
> -	for_each_cpu(cpu, cpus)
> -		if (!freq_counters_valid(cpu))
> +	for_each_cpu(cpu, cpus) {
> +		if (!freq_counters_valid(cpu)) {
> +			topology_clear_scale_freq_source(SCALE_FREQ_SOURCE_ARCH, cpus);
>  			return;
> +		}
> +	}
>  
>  	if (!cpumask_available(amu_fie_cpus) &&
>  	    !zalloc_cpumask_var(&amu_fie_cpus, GFP_KERNEL)) {
> @@ -385,7 +388,7 @@ static int init_amu_fie_callback(struct notifier_block *nb, unsigned long val,
>  	struct cpufreq_policy *policy = data;
>  
>  	if (val == CPUFREQ_CREATE_POLICY)
> -		amu_fie_setup(policy->related_cpus);
> +		amu_fie_setup(policy->cpus);
>  
>  	/*
>  	 * We don't need to handle CPUFREQ_REMOVE_POLICY event as the AMU
> @@ -404,10 +407,46 @@ static struct notifier_block init_amu_fie_notifier = {
>  	.notifier_call = init_amu_fie_callback,
>  };
>  
> +static int cpuhp_topology_online(unsigned int cpu)
> +{
> +	struct cpufreq_policy *policy __free(put_cpufreq_policy);
> +	cpumask_var_t cpus_to_set;
> +
> +	if (!zalloc_cpumask_var(&cpus_to_set, GFP_KERNEL))
> +		return -ENOMEM;
> +
> +	cpumask_copy(cpus_to_set, cpumask_of(cpu));
> +
> +	policy = cpufreq_cpu_get(cpu);
> +	if (policy) {
> +		cpumask_or(cpus_to_set, cpus_to_set, policy->cpus);
> +		amu_fie_setup(cpus_to_set);
> +	}
> +
> +	free_cpumask_var(cpus_to_set);

What am I missing here as I don't see the need to for this local
copy  `cpus_to_set`.

Why can't you just call
	policy = cpufreq_cpu_get(cpu);
	if (policy)
		amu_fie_setup(cpus_to_set);


> +	return 0;
> +}
> +
>  static int __init init_amu_fie(void)
>  {
> -	return cpufreq_register_notifier(&init_amu_fie_notifier,
> +	int ret;
> +
> +	ret = cpufreq_register_notifier(&init_amu_fie_notifier,
>  					CPUFREQ_POLICY_NOTIFIER);
> +	if (ret)
> +		return ret;
> +
> +	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
> +					"arm64/topology:online",
> +					cpuhp_topology_online,
> +					NULL);
> +	if (ret < 0) {
> +		cpufreq_unregister_notifier(&init_amu_fie_notifier,
> +					    CPUFREQ_POLICY_NOTIFIER);
> +		return ret;
> +	}
> +

Why can't you just set up cpuhp_* first and then cpufreq notifier to avoid
this unregistering ?

-- 
Regards,
Sudeep

Re: [PATCH v2] arm64: topology: Setup AMU FIE for online CPUs only

[zhenglifeng (A)]

On 2025/7/25 21:11, Sudeep Holla wrote:
> On Fri, Jul 25, 2025 at 06:28:13PM +0800, Lifeng Zheng wrote:
>> When boot with maxcpu=1 restrict, and LPI(Low Power Idle States) is on,
>> only CPU0 will go online. The support AMU flag of CPU0 will be set but the
>> flags of other CPUs will not. This will cause AMU FIE set up fail for CPU0
>> when it shares a cpufreq policy with other CPU(s). After that, when other
>> CPUs are finally online and the support AMU flags of them are set, they'll
>> never have a chance to set up AMU FIE, even though they're eligible.
>>
>> To solve this problem, the process of setting up AMU FIE needs to be
>> modified as follows:
>>
>> 1. Set up AMU FIE only for the online CPUs.
>>
>> 2. Try to set up AMU FIE each time a CPU goes online and do the
>> freq_counters_valid() check for all the online CPUs share the same policy.
>> If this check fails, clear scale freq source of these CPUs, in case they
>> use different source of the freq scale.
>>
>> Signed-off-by: Lifeng Zheng <zhenglifeng1@huawei.com>
>> ---
> 
> I have no idea what changed from v1->v2 and no link to v1 for me to
> refer to it and check the delta 🙁.

My fault.

Changes in v2:

 - keep init_amu_fie_notifier for setting up AMU FIE when the cpufreq
   policy is being created
 - set up AMU FIE only for online CPUs instead of related_cpus in
   init_amu_fie_callback()
 - check and set all the online CPUs in the same policy when hotplug one
 - clear scale freq source for all the online CPUs in the same policy to
   avoid using different source of the freq scale

---
Discussions of previous version:
v1: https://lore.kernel.org/all/20250607094533.416368-1-zhenglifeng1@huawei.com/

> 
>>  arch/arm64/kernel/topology.c | 49 ++++++++++++++++++++++++++++++++----
>>  1 file changed, 44 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
>> index 5d07ee85bdae..d578c496d457 100644
>> --- a/arch/arm64/kernel/topology.c
>> +++ b/arch/arm64/kernel/topology.c
>> @@ -357,12 +357,15 @@ static void amu_fie_setup(const struct cpumask *cpus)
>>  
>>  	/* We are already set since the last insmod of cpufreq driver */
>>  	if (cpumask_available(amu_fie_cpus) &&
>> -	    unlikely(cpumask_subset(cpus, amu_fie_cpus)))
>> +	    cpumask_subset(cpus, amu_fie_cpus))
>>  		return;
>>  
>> -	for_each_cpu(cpu, cpus)
>> -		if (!freq_counters_valid(cpu))
>> +	for_each_cpu(cpu, cpus) {
>> +		if (!freq_counters_valid(cpu)) {
>> +			topology_clear_scale_freq_source(SCALE_FREQ_SOURCE_ARCH, cpus);
>>  			return;
>> +		}
>> +	}
>>  
>>  	if (!cpumask_available(amu_fie_cpus) &&
>>  	    !zalloc_cpumask_var(&amu_fie_cpus, GFP_KERNEL)) {
>> @@ -385,7 +388,7 @@ static int init_amu_fie_callback(struct notifier_block *nb, unsigned long val,
>>  	struct cpufreq_policy *policy = data;
>>  
>>  	if (val == CPUFREQ_CREATE_POLICY)
>> -		amu_fie_setup(policy->related_cpus);
>> +		amu_fie_setup(policy->cpus);
>>  
>>  	/*
>>  	 * We don't need to handle CPUFREQ_REMOVE_POLICY event as the AMU
>> @@ -404,10 +407,46 @@ static struct notifier_block init_amu_fie_notifier = {
>>  	.notifier_call = init_amu_fie_callback,
>>  };
>>  
>> +static int cpuhp_topology_online(unsigned int cpu)
>> +{
>> +	struct cpufreq_policy *policy __free(put_cpufreq_policy);
>> +	cpumask_var_t cpus_to_set;
>> +
>> +	if (!zalloc_cpumask_var(&cpus_to_set, GFP_KERNEL))
>> +		return -ENOMEM;
>> +
>> +	cpumask_copy(cpus_to_set, cpumask_of(cpu));
>> +
>> +	policy = cpufreq_cpu_get(cpu);
>> +	if (policy) {
>> +		cpumask_or(cpus_to_set, cpus_to_set, policy->cpus);
>> +		amu_fie_setup(cpus_to_set);
>> +	}
>> +
>> +	free_cpumask_var(cpus_to_set);
> 
> What am I missing here as I don't see the need to for this local
> copy  `cpus_to_set`.
> 
> Why can't you just call
> 	policy = cpufreq_cpu_get(cpu);
> 	if (policy)
> 		amu_fie_setup(cpus_to_set);

As mentioned in the commit log, when hotplug a CPU, the
freq_counters_valid() check should be done for all the online CPUs share
the same policy. Otherwise they may use different source of the freq scale
and cause some problems.

> 
> 
>> +	return 0;
>> +}
>> +
>>  static int __init init_amu_fie(void)
>>  {
>> -	return cpufreq_register_notifier(&init_amu_fie_notifier,
>> +	int ret;
>> +
>> +	ret = cpufreq_register_notifier(&init_amu_fie_notifier,
>>  					CPUFREQ_POLICY_NOTIFIER);
>> +	if (ret)
>> +		return ret;
>> +
>> +	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
>> +					"arm64/topology:online",
>> +					cpuhp_topology_online,
>> +					NULL);
>> +	if (ret < 0) {
>> +		cpufreq_unregister_notifier(&init_amu_fie_notifier,
>> +					    CPUFREQ_POLICY_NOTIFIER);
>> +		return ret;
>> +	}
>> +
> 
> Why can't you just set up cpuhp_* first and then cpufreq notifier to avoid
> this unregistering ?

If set up cpuhp state first, it should be remove when register notifier
fails. So I think there is no difference which one is called first.

Re: [PATCH v2] arm64: topology: Setup AMU FIE for online CPUs only

[Beata Michalska]

Hi Lifeng,

Apologies for late reply.

On Fri, Jul 25, 2025 at 06:28:13PM +0800, Lifeng Zheng wrote:
> When boot with maxcpu=1 restrict, and LPI(Low Power Idle States) is on,
> only CPU0 will go online. The support AMU flag of CPU0 will be set but the
> flags of other CPUs will not. This will cause AMU FIE set up fail for CPU0
> when it shares a cpufreq policy with other CPU(s). After that, when other
> CPUs are finally online and the support AMU flags of them are set, they'll
> never have a chance to set up AMU FIE, even though they're eligible.
> 
> To solve this problem, the process of setting up AMU FIE needs to be
> modified as follows:
> 
> 1. Set up AMU FIE only for the online CPUs.
> 
> 2. Try to set up AMU FIE each time a CPU goes online and do the
> freq_counters_valid() check for all the online CPUs share the same policy.
> If this check fails, clear scale freq source of these CPUs, in case they
> use different source of the freq scale.
> 
> Signed-off-by: Lifeng Zheng <zhenglifeng1@huawei.com>
> ---
>  arch/arm64/kernel/topology.c | 49 ++++++++++++++++++++++++++++++++----
>  1 file changed, 44 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> index 5d07ee85bdae..d578c496d457 100644
> --- a/arch/arm64/kernel/topology.c
> +++ b/arch/arm64/kernel/topology.c
> @@ -357,12 +357,15 @@ static void amu_fie_setup(const struct cpumask *cpus)
>  
>  	/* We are already set since the last insmod of cpufreq driver */
>  	if (cpumask_available(amu_fie_cpus) &&
> -	    unlikely(cpumask_subset(cpus, amu_fie_cpus)))
> +	    cpumask_subset(cpus, amu_fie_cpus))
>  		return;
>  
> -	for_each_cpu(cpu, cpus)
> -		if (!freq_counters_valid(cpu))
> +	for_each_cpu(cpu, cpus) {
> +		if (!freq_counters_valid(cpu)) {
> +			topology_clear_scale_freq_source(SCALE_FREQ_SOURCE_ARCH, cpus);
>  			return;
> +		}
> +	}
>  
>  	if (!cpumask_available(amu_fie_cpus) &&
>  	    !zalloc_cpumask_var(&amu_fie_cpus, GFP_KERNEL)) {
> @@ -385,7 +388,7 @@ static int init_amu_fie_callback(struct notifier_block *nb, unsigned long val,
>  	struct cpufreq_policy *policy = data;
>  
>  	if (val == CPUFREQ_CREATE_POLICY)
> -		amu_fie_setup(policy->related_cpus);
> +		amu_fie_setup(policy->cpus);
Right, so this will only work for the AMU side of things. The cpufreq core still
considers `related_cpus` which should be aligned (if possible).
>  
>  	/*
>  	 * We don't need to handle CPUFREQ_REMOVE_POLICY event as the AMU
> @@ -404,10 +407,46 @@ static struct notifier_block init_amu_fie_notifier = {
>  	.notifier_call = init_amu_fie_callback,
>  };
>  
> +static int cpuhp_topology_online(unsigned int cpu)
> +{
> +	struct cpufreq_policy *policy __free(put_cpufreq_policy);
> +	cpumask_var_t cpus_to_set;
> +
> +	if (!zalloc_cpumask_var(&cpus_to_set, GFP_KERNEL))
> +		return -ENOMEM;
> +
> +	cpumask_copy(cpus_to_set, cpumask_of(cpu));
> +
> +	policy = cpufreq_cpu_get(cpu);
> +	if (policy) {
> +		cpumask_or(cpus_to_set, cpus_to_set, policy->cpus);
This should be available via `amu_fie_cpus` mask (as of subset).
So it should be enough to test only the CPU at hand?
Additionally there is no tracking whether that CPU hasn't been verified already.
> +		amu_fie_setup(cpus_to_set);
> +	}
> +
> +	free_cpumask_var(cpus_to_set);
> +	return 0;
> +}
> +
>  static int __init init_amu_fie(void)
>  {
> -	return cpufreq_register_notifier(&init_amu_fie_notifier,
> +	int ret;
> +
> +	ret = cpufreq_register_notifier(&init_amu_fie_notifier,
>  					CPUFREQ_POLICY_NOTIFIER);
> +	if (ret)
> +		return ret;
> +
> +	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
> +					"arm64/topology:online",
> +					cpuhp_topology_online,
> +					NULL);
We should check whether we really have to set it up, as of all CPUs are already
online).
> +	if (ret < 0) {
> +		cpufreq_unregister_notifier(&init_amu_fie_notifier,
> +					    CPUFREQ_POLICY_NOTIFIER);
> +		return ret;
> +	}
> +
> +	return 0;
>  }
>  core_initcall(init_amu_fie);
>  
> -- 
> 2.33.0
> 

Re: [PATCH v2] arm64: topology: Setup AMU FIE for online CPUs only

[zhenglifeng (A)]

On 2025/7/31 16:44, Beata Michalska wrote:

> Hi Lifeng,
> 
> Apologies for late reply.
> 
> On Fri, Jul 25, 2025 at 06:28:13PM +0800, Lifeng Zheng wrote:
>> When boot with maxcpu=1 restrict, and LPI(Low Power Idle States) is on,
>> only CPU0 will go online. The support AMU flag of CPU0 will be set but the
>> flags of other CPUs will not. This will cause AMU FIE set up fail for CPU0
>> when it shares a cpufreq policy with other CPU(s). After that, when other
>> CPUs are finally online and the support AMU flags of them are set, they'll
>> never have a chance to set up AMU FIE, even though they're eligible.
>>
>> To solve this problem, the process of setting up AMU FIE needs to be
>> modified as follows:
>>
>> 1. Set up AMU FIE only for the online CPUs.
>>
>> 2. Try to set up AMU FIE each time a CPU goes online and do the
>> freq_counters_valid() check for all the online CPUs share the same policy.
>> If this check fails, clear scale freq source of these CPUs, in case they
>> use different source of the freq scale.
>>
>> Signed-off-by: Lifeng Zheng <zhenglifeng1@huawei.com>
>> ---
>>  arch/arm64/kernel/topology.c | 49 ++++++++++++++++++++++++++++++++----
>>  1 file changed, 44 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
>> index 5d07ee85bdae..d578c496d457 100644
>> --- a/arch/arm64/kernel/topology.c
>> +++ b/arch/arm64/kernel/topology.c
>> @@ -357,12 +357,15 @@ static void amu_fie_setup(const struct cpumask *cpus)
>>  
>>  	/* We are already set since the last insmod of cpufreq driver */
>>  	if (cpumask_available(amu_fie_cpus) &&
>> -	    unlikely(cpumask_subset(cpus, amu_fie_cpus)))
>> +	    cpumask_subset(cpus, amu_fie_cpus))
>>  		return;
>>  
>> -	for_each_cpu(cpu, cpus)
>> -		if (!freq_counters_valid(cpu))
>> +	for_each_cpu(cpu, cpus) {
>> +		if (!freq_counters_valid(cpu)) {
>> +			topology_clear_scale_freq_source(SCALE_FREQ_SOURCE_ARCH, cpus);
>>  			return;
>> +		}
>> +	}
>>  
>>  	if (!cpumask_available(amu_fie_cpus) &&
>>  	    !zalloc_cpumask_var(&amu_fie_cpus, GFP_KERNEL)) {
>> @@ -385,7 +388,7 @@ static int init_amu_fie_callback(struct notifier_block *nb, unsigned long val,
>>  	struct cpufreq_policy *policy = data;
>>  
>>  	if (val == CPUFREQ_CREATE_POLICY)
>> -		amu_fie_setup(policy->related_cpus);
>> +		amu_fie_setup(policy->cpus);
> Right, so this will only work for the AMU side of things. The cpufreq core still
> considers `related_cpus` which should be aligned (if possible).

'cpus' means the online CPUs relate to this policy, and 'related_cpus'
means all the CPUs relate to this policy. Use 'cpus' here because AMU FIE
only needs to be set for the online CPUs. As for the offline CPUs, they
don't have to set up AMU FIE, and shouldn't affect other CPUs setting up
AMU FIE.

>>  
>>  	/*
>>  	 * We don't need to handle CPUFREQ_REMOVE_POLICY event as the AMU
>> @@ -404,10 +407,46 @@ static struct notifier_block init_amu_fie_notifier = {
>>  	.notifier_call = init_amu_fie_callback,
>>  };
>>  
>> +static int cpuhp_topology_online(unsigned int cpu)
>> +{
>> +	struct cpufreq_policy *policy __free(put_cpufreq_policy);
>> +	cpumask_var_t cpus_to_set;
>> +
>> +	if (!zalloc_cpumask_var(&cpus_to_set, GFP_KERNEL))
>> +		return -ENOMEM;
>> +
>> +	cpumask_copy(cpus_to_set, cpumask_of(cpu));
>> +
>> +	policy = cpufreq_cpu_get(cpu);
>> +	if (policy) {
>> +		cpumask_or(cpus_to_set, cpus_to_set, policy->cpus);
> This should be available via `amu_fie_cpus` mask (as of subset).
> So it should be enough to test only the CPU at hand?

Yeah, makes sense. Thanks.

> Additionally there is no tracking whether that CPU hasn't been verified already.

I don't think it's necessary. If a CPU has been verified already and pass,
then the 'amu_fie_cpus' mask should contain it, otherwise it deserves to be
checked again.

>> +		amu_fie_setup(cpus_to_set);
>> +	}
>> +
>> +	free_cpumask_var(cpus_to_set);
>> +	return 0;
>> +}
>> +
>>  static int __init init_amu_fie(void)
>>  {
>> -	return cpufreq_register_notifier(&init_amu_fie_notifier,
>> +	int ret;
>> +
>> +	ret = cpufreq_register_notifier(&init_amu_fie_notifier,
>>  					CPUFREQ_POLICY_NOTIFIER);
>> +	if (ret)
>> +		return ret;
>> +
>> +	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
>> +					"arm64/topology:online",
>> +					cpuhp_topology_online,
>> +					NULL);
> We should check whether we really have to set it up, as of all CPUs are already
> online).

All CPUs are likely to be online at this point. However, we cannot
guarantee that this is still the case when the cpufreq policies are
created.

>> +	if (ret < 0) {
>> +		cpufreq_unregister_notifier(&init_amu_fie_notifier,
>> +					    CPUFREQ_POLICY_NOTIFIER);
>> +		return ret;
>> +	}
>> +
>> +	return 0;
>>  }
>>  core_initcall(init_amu_fie);
>>  
>> -- 
>> 2.33.0
>>
>