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 6b649031808f..ab8dd5cdb13b 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 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) {
+			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;
+
+	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 20f3d62e7a16..213bd389ec57 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;
-- 
2.34.1