ACPI / CPPC: Add a helper to get desired performance

This patch add a helper to get the value of desired performance
register.

Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
[ rjw: More white space ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/cppc_acpi.c

@@ -1050,6 +1050,48 @@ static int cpc_write(int cpu, struct cpc_register_resource *reg_res, u64 val)
 	return ret_val;
 }
 
+/**
+ * cppc_get_desired_perf - Get the value of desired performance register.
+ * @cpunum: CPU from which to get desired performance.
+ * @desired_perf: address of a variable to store the returned desired performance
+ *
+ * Return: 0 for success, -EIO otherwise.
+ */
+int cppc_get_desired_perf(int cpunum, u64 *desired_perf)
+{
+	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpunum);
+	int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpunum);
+	struct cpc_register_resource *desired_reg;
+	struct cppc_pcc_data *pcc_ss_data = NULL;
+
+	desired_reg = &cpc_desc->cpc_regs[DESIRED_PERF];
+
+	if (CPC_IN_PCC(desired_reg)) {
+		int ret = 0;
+
+		if (pcc_ss_id < 0)
+			return -EIO;
+
+		pcc_ss_data = pcc_data[pcc_ss_id];
+
+		down_write(&pcc_ss_data->pcc_lock);
+
+		if (send_pcc_cmd(pcc_ss_id, CMD_READ) >= 0)
+			cpc_read(cpunum, desired_reg, desired_perf);
+		else
+			ret = -EIO;
+
+		up_write(&pcc_ss_data->pcc_lock);
+
+		return ret;
+	}
+
+	cpc_read(cpunum, desired_reg, desired_perf);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(cppc_get_desired_perf);
+
 /**
  * cppc_get_perf_caps - Get a CPUs performance capabilities.
  * @cpunum: CPU from which to get capabilities info.

include/acpi/cppc_acpi.h

@@ -137,6 +137,7 @@ struct cppc_cpudata {
 	cpumask_var_t shared_cpu_map;
 };
 
+extern int cppc_get_desired_perf(int cpunum, u64 *desired_perf);
 extern int cppc_get_perf_ctrs(int cpu, struct cppc_perf_fb_ctrs *perf_fb_ctrs);
 extern int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls);
 extern int cppc_get_perf_caps(int cpu, struct cppc_perf_caps *caps);