Re: [PATCH v6 4/9] ACPI: CPPC: Add cppc_get_perf() API to read performance controls

[Pierre Gondois <pierre.gondois@arm.com>]

On 1/22/26 09:56, zhenglifeng (A) wrote:
> On 2026/1/20 22:56, Sumit Gupta wrote:
>> Add cppc_get_perf() function to read values of performance control
>> registers including desired_perf, min_perf, max_perf, energy_perf,
>> and auto_sel.
>>
>> This provides a read interface to complement the existing
>> cppc_set_perf() write interface for performance control registers.
>>
>> Note that auto_sel is read by cppc_get_perf() but not written by
>> cppc_set_perf() to avoid unintended mode changes during performance
>> updates. It can be updated with existing dedicated cppc_set_auto_sel()
>> API.
>>
>> Use cppc_get_perf() in cppc_cpufreq_get_cpu_data() to initialize
>> perf_ctrls with current hardware register values during cpufreq
>> policy initialization.
>>
>> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
>> ---
>>   drivers/acpi/cppc_acpi.c       | 80 ++++++++++++++++++++++++++++++++++
>>   drivers/cpufreq/cppc_cpufreq.c |  6 +++
>>   include/acpi/cppc_acpi.h       |  5 +++
>>   3 files changed, 91 insertions(+)
>>
>> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
>> index a09bdabaa804..de35aeb07833 100644
>> --- a/drivers/acpi/cppc_acpi.c
>> +++ b/drivers/acpi/cppc_acpi.c
>> @@ -1739,6 +1739,86 @@ int cppc_set_enable(int cpu, bool enable)
>>   }
>>   EXPORT_SYMBOL_GPL(cppc_set_enable);
>>   
>> +/**
>> + * cppc_get_perf - Get a CPU's performance controls.
>> + * @cpu: CPU for which to get performance controls.
>> + * @perf_ctrls: ptr to cppc_perf_ctrls. See cppc_acpi.h
>> + *
>> + * Return: 0 for success with perf_ctrls, -ERRNO otherwise.
>> + */
>> +int cppc_get_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
>> +{
>> +	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
>> +	struct cpc_register_resource *desired_perf_reg,
>> +				     *min_perf_reg, *max_perf_reg,
>> +				     *energy_perf_reg, *auto_sel_reg;
>> +	u64 desired_perf = 0, min = 0, max = 0, energy_perf = 0, auto_sel = 0;
>> +	int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpu);
>> +	struct cppc_pcc_data *pcc_ss_data = NULL;
>> +	int ret = 0, regs_in_pcc = 0;
>> +
>> +	if (!cpc_desc) {
>> +		pr_debug("No CPC descriptor for CPU:%d\n", cpu);
>> +		return -ENODEV;
>> +	}
>> +
>> +	if (!perf_ctrls) {
>> +		pr_debug("Invalid perf_ctrls pointer\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	desired_perf_reg = &cpc_desc->cpc_regs[DESIRED_PERF];
>> +	min_perf_reg = &cpc_desc->cpc_regs[MIN_PERF];
>> +	max_perf_reg = &cpc_desc->cpc_regs[MAX_PERF];
>> +	energy_perf_reg = &cpc_desc->cpc_regs[ENERGY_PERF];
>> +	auto_sel_reg = &cpc_desc->cpc_regs[AUTO_SEL_ENABLE];
>> +
>> +	/* Are any of the regs PCC ?*/
>> +	if (CPC_IN_PCC(desired_perf_reg) || CPC_IN_PCC(min_perf_reg) ||
>> +	    CPC_IN_PCC(max_perf_reg) || CPC_IN_PCC(energy_perf_reg) ||
>> +	    CPC_IN_PCC(auto_sel_reg)) {
>> +		if (pcc_ss_id < 0) {
>> +			pr_debug("Invalid pcc_ss_id for CPU:%d\n", cpu);
>> +			return -ENODEV;
>> +		}
>> +		pcc_ss_data = pcc_data[pcc_ss_id];
>> +		regs_in_pcc = 1;
>> +		down_write(&pcc_ss_data->pcc_lock);
>> +		/* Ring doorbell once to update PCC subspace */
>> +		if (send_pcc_cmd(pcc_ss_id, CMD_READ) < 0) {
>> +			ret = -EIO;
>> +			goto out_err;
>> +		}
>> +	}
>> +
>> +	/* Read optional elements if present */
>> +	if (CPC_SUPPORTED(max_perf_reg))
>> +		cpc_read(cpu, max_perf_reg, &max);
>> +	perf_ctrls->max_perf = max;
>> +
>> +	if (CPC_SUPPORTED(min_perf_reg))
>> +		cpc_read(cpu, min_perf_reg, &min);
>> +	perf_ctrls->min_perf = min;
>> +
>> +	if (CPC_SUPPORTED(desired_perf_reg))
>> +		cpc_read(cpu, desired_perf_reg, &desired_perf);
>> +	perf_ctrls->desired_perf = desired_perf;
> desired_perf_reg is not an optional one, so it has to be supported.

The ACPI spec seems to say it is optional under some circumstances.

Cf:
"""
This register is optional when OSPM
indicates support for CPPC2 in the platform-wide _OSC
capabilities and the Autonomous Selection Enable reg-
ister is Integer 1
"""


Maybe it is ok to let this check here and to a more complex verification
in acpi_cppc_processor_probe()


>
>> +
>> +	if (CPC_SUPPORTED(energy_perf_reg))
>> +		cpc_read(cpu, energy_perf_reg, &energy_perf);
>> +	perf_ctrls->energy_perf = energy_perf;
>> +
>> +	if (CPC_SUPPORTED(auto_sel_reg))
>> +		cpc_read(cpu, auto_sel_reg, &auto_sel);
>> +	perf_ctrls->auto_sel = (bool)auto_sel;
>> +
>> +out_err:
>> +	if (regs_in_pcc)
>> +		up_write(&pcc_ss_data->pcc_lock);
>> +	return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(cppc_get_perf);
>> +
>>   /**
>>    * cppc_set_perf - Set a CPU's performance controls.
>>    * @cpu: CPU for which to set performance controls.
>> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
>> index c95dcd7719c3..229880c4eedb 100644
>> --- a/drivers/cpufreq/cppc_cpufreq.c
>> +++ b/drivers/cpufreq/cppc_cpufreq.c
>> @@ -594,6 +594,12 @@ 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;
>> +	}
>> +
>>   	return cpu_data;
>>   
>>   free_mask:
>> diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
>> index 4d644f03098e..3fc796c0d902 100644
>> --- a/include/acpi/cppc_acpi.h
>> +++ b/include/acpi/cppc_acpi.h
>> @@ -151,6 +151,7 @@ extern int cppc_get_desired_perf(int cpunum, u64 *desired_perf);
>>   extern int cppc_get_nominal_perf(int cpunum, u64 *nominal_perf);
>>   extern int cppc_get_highest_perf(int cpunum, u64 *highest_perf);
>>   extern int cppc_get_perf_ctrs(int cpu, struct cppc_perf_fb_ctrs *perf_fb_ctrs);
>> +extern int cppc_get_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls);
>>   extern int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls);
>>   extern int cppc_set_enable(int cpu, bool enable);
>>   extern int cppc_get_perf_caps(int cpu, struct cppc_perf_caps *caps);
>> @@ -193,6 +194,10 @@ static inline int cppc_get_perf_ctrs(int cpu, struct cppc_perf_fb_ctrs *perf_fb_
>>   {
>>   	return -EOPNOTSUPP;
>>   }
>> +static inline int cppc_get_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
>> +{
>> +	return -EOPNOTSUPP;
>> +}
>>   static inline int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
>>   {
>>   	return -EOPNOTSUPP;