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

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

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.


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.


> +	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);
>   
>   /**
>    * cppc_set_perf - Set a CPU's performance controls.
> diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
> index 13fa81504844..7190afeead8b 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);
> @@ -192,6 +193,10 @@ 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;