[PATCH v5 03/11] ACPI: CPPC: Add cppc_get_perf() API to read performance controls

Sumit Gupta
2025-12-23T12:14:06Z

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.

Also call cppc_get_perf() in cppc_cpufreq_get_cpu_data() to initialize
perf_ctrls with current hardware register values during cpufreq
initialization for each CPU policy.

Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
---
drivers/acpi/cppc_acpi.c | 79 ++++++++++++++++++++++++++++++++++
drivers/cpufreq/cppc_cpufreq.c | 6 +++
include/acpi/cppc_acpi.h | 5 +++
3 files changed, 90 insertions(+)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index e66e20d1f31b..a4e89fe6aab5 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1732,6 +1732,85 @@ 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, *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;
+
+ 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.
diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 7c26ce554e29..a87e7bb2e2f1 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -562,6 +562,12 @@ 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 a090b010f5f1..12a1dc31bf2a 100644
--- a/include/acpi/cppc_acpi.h
+++ b/include/acpi/cppc_acpi.h
@@ -150,6 +150,7 @@ 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);
@@ -191,6 +192,10 @@ 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;
--
2.34.1