[PATCH v6 0/3] arm64: topology: Handle AMU FIE setup on CPU hotplug

[zhenglifeng (A)]

On 2025/12/2 23:31, Beata Michalska wrote:
> On Tue, Dec 02, 2025 at 11:05:25AM +0800, zhenglifeng (A) wrote:
>> On 2025/12/1 23:27, Beata Michalska wrote:
>>> Hi,
>>>
>>> Apologies for the delay in reviewing this - currently in progress....
>>> Out of curiosity: what's the cpufreq driver used for testing this series ?
>>
>> I used cppc_cpufreq for testing this. But with some modifications in
>> processor_driver.c, or you'll find that the driver will fail to load with
>> maxcpus set. The modification below is only a temporary solution. I'm still
>> working on that.
>>
> Right, so overall the implementation looks good - thanks for that.
> There are two issues though with the cppc cpufreq driver.
> 
> One: as you have already noticed - it fails to register when
> cpumask_present != cpumask_online.
> 
> Second: it will mix the sources of the freq scale if not all CPUs within the
> policy have AMUs enabled/valid. This is due to the fact that at the time of
> registering the driver and initializing the FIE support policy->cpus ==
> policy->related_cpus. Assuming scenario when there are two CPUs within the
> policy, one being offline and missing valid AMU counters,
> the topology_set_scale_freq_source from cppc cpufreq driver will register
> the tick handler for both CPUs, whereas AMU support will (rightly so) register
> only for the firs one. When the second CPU comes online, the mismatch will be
> detected and the arch callback will get cleared for the first CPU, but the
> second one will remain unchanged.

Thanks for pointing them out. I'll try to fix these issues after this series.

> 
> That said, I do not think any of those issues is a blocker for this series.
> But both would need fixing.
> 
> ---
> BR
> Beata
> 
> 
>> ---
>> diff --git a/drivers/acpi/processor_driver.c b/drivers/acpi/processor_driver.c
>> index 5d824435b26b..2f286a1b0b02 100644
>> --- a/drivers/acpi/processor_driver.c
>> +++ b/drivers/acpi/processor_driver.c
>> @@ -33,6 +33,7 @@ MODULE_AUTHOR("Paul Diefenbaugh");
>>  MODULE_DESCRIPTION("ACPI Processor Driver");
>>  MODULE_LICENSE("GPL");
>>  
>> +static int acpi_processor_start(struct device *dev);
>>  static int acpi_processor_stop(struct device *dev);
>>  
>>  static const struct acpi_device_id processor_device_ids[] = {
>> @@ -46,6 +47,7 @@ static struct device_driver acpi_processor_driver = {
>>  	.name = "processor",
>>  	.bus = &cpu_subsys,
>>  	.acpi_match_table = processor_device_ids,
>> +	.probe = acpi_processor_start,
>>  	.remove = acpi_processor_stop,
>>  };
>>  
>> @@ -191,6 +193,21 @@ static int __acpi_processor_start(struct acpi_device *device)
>>  	return result;
>>  }
>>  
>> +static int acpi_processor_start(struct device *dev)
>> +{
>> +	struct acpi_device *device = ACPI_COMPANION(dev);
>> +	int ret;
>> +
>> +	if (!device)
>> +		return -ENODEV;
>> +
>> +	/* Protect against concurrent CPU hotplug operations */
>> +	cpu_hotplug_disable();
>> +	ret = __acpi_processor_start(device);
>> +	cpu_hotplug_enable();
>> +	return ret;
>> +}
>> +
>>  static int acpi_processor_stop(struct device *dev)
>>  {
>>  	struct acpi_device *device = ACPI_COMPANION(dev);
>> @@ -264,9 +281,9 @@ static int __init acpi_processor_driver_init(void)
>>  
>>  	acpi_processor_register_idle_driver();
>>  
>> -	result = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
>> -				   "acpi/cpu-drv:online",
>> -				   acpi_soft_cpu_online, NULL);
>> +	result = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
>> +					   "acpi/cpu-drv:online",
>> +					   acpi_soft_cpu_online, NULL);
>>  	if (result < 0)
>>  		goto err;
>>  	hp_online = result;
>>
>>>
>>> ---
>>> BR
>>> Beata
>>> On Wed, Nov 19, 2025 at 04:13:53PM +0800, Lifeng Zheng wrote:
>>>> Solve a problem that causes CPUs Setup AMU FIE failed in a corner case,
>>>> even though they're eligible.
>>>>
>>>>
>>>
>>
>