Re: [PATCH v4 2/8] ACPI: CPPC: Add cppc_get_perf() API to read performance controls

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

Hello Sumit,

On 11/28/25 15:01, Sumit Gupta wrote:
> Hi Pierre,
>
>
> On 27/11/25 20:23, Pierre Gondois wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> Hello Sumit,
>>
>> Sorry for the late review.
>> I think it would be nice to split the patchset in 2 as handling the
>> auto_sel and
>> min/max_perf values in the cppc_cpufreq driver might lead to more
>> discussion.
>> I.e. the ACPI: CPPC: XXX patches should be straightforward to upstream.
>> This is just a personal opinion, feel free to ignore it.
>>
>
> I think its better to keep the changes in one patchset for better 
> context.
> I agree that the 'ACPI: CPPC: XX' patches can be applied first if ACK'ed.
> Will update the cover letter in v5 to request for taking those patches
> first if no new issues and send v6 with changes on the rest of patches
> if any new comments on them.

Ok sure


>
>
>>
>> On 11/5/25 12:38, Sumit Gupta wrote:
>>> Add cppc_get_perf() function to read values of performance control
>>> registers including desired_perf, min_perf, max_perf, and energy_perf.
>>>
>>> This provides a read interface to complement the existing 
>>> cppc_set_perf()
>>> write interface for performance control registers.
>>>
>>> Signed-off-by: Sumit Gupta<sumitg@nvidia.com>
>>> ---
>>>   drivers/acpi/cppc_acpi.c | 73 
>>> ++++++++++++++++++++++++++++++++++++++++
>>>   include/acpi/cppc_acpi.h |  5 +++
>>>   2 files changed, 78 insertions(+)
>>>
>>> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
>>> index ab4651205e8a..05672c30187c 100644
>>> --- a/drivers/acpi/cppc_acpi.c
>>> +++ b/drivers/acpi/cppc_acpi.c
>>> @@ -1731,6 +1731,79 @@ int cppc_set_enable(int cpu, bool enable)
>>>       return cppc_set_reg_val(cpu, ENABLE, 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;
>>> +     u64 desired_perf = 0, min = 0, max = 0, energy_perf = 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];
>>> +
>>> +     /* 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)) {
>>> +             if (pcc_ss_id < 0) {
>>> +                     pr_debug("Invalid pcc_ss_id forCPU:%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) {
>>> +                     pr_debug("Failed to send PCC command for 
>>> CPU:%d, ret:%d\n", cpu, ret);
>>> +                     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;
>>> +
>>
>> NIT: I think the 'desired_perf_reg' register is mandatory, so the check
>> could be removed.
>>
>>
>
> The register is optional when Autonomous mode is enabled.
> As per CPPC spec:
> "This register is optional when OSPM indicates support for CPPC2 in the
> platform-wide _OSC capabilities and the Autonomous Selection Enable
> register is Integer 1"

Yes, right indeed,

Regards,
Pierre


>
> Thank you,
> Sumit Gupta
>
>
>>> +     if (CPC_SUPPORTED(desired_perf_reg))
>>> +             cpc_read(cpu, desired_perf_reg, &desired_perf);
>>> +     perf_ctrls->desired_perf = desired_perf;
>>> +
>>> +     if (CPC_SUPPORTED(energy_perf_reg))
>>> +             cpc_read(cpu, energy_perf_reg, &energy_perf);
>>> +     perf_ctrls->energy_perf = energy_perf;
>>> +
>>> +out_err:
>>> +     if (regs_in_pcc)
>>> +             up_write(&pcc_ss_data->pcc_lock);
>>> +     return ret;
>>> +}
>>> +EXPORT_SYMBOL_GPL(cppc_get_perf);
>
> ....
>