[PATCH] ACPI: CPPC: Add helper to get effective guaranteed performance

According to the ACPI CPPC specification, if the Guaranteed
Performance register is not implemented, OSPM assumes the
guaranteed performance is equal to nominal performance.

Add cppc_get_effective_guaranteed_perf() helper to provide a
spec-compliant effective guaranteed performance value while
preserving the raw values returned by cppc_get_perf_caps().

Signed-off-by: Xueqin Luo <[email protected]>
---
 drivers/acpi/cppc_acpi.c       | 26 ++++++++++++++++++++++++++
 drivers/cpufreq/intel_pstate.c | 10 ++++------
 include/acpi/cppc_acpi.h       |  5 +++++
 3 files changed, 35 insertions(+), 6 deletions(-)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index f370be8715ae..6dc11030707a 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1328,6 +1328,32 @@ int cppc_get_highest_perf(int cpunum, u64 *highest_perf)
 }
 EXPORT_SYMBOL_GPL(cppc_get_highest_perf);
 
+/**
+ * cppc_get_effective_guaranteed_perf - get effective guaranteed performance
+ * @cpunum: CPU number
+ * @guaranteed_perf: Effective guaranteed performance value
+ *
+ * The ACPI CPPC specification states that if the Guaranteed
+ * Performance register is not implemented, OSPM assumes the
+ * guaranteed performance is equal to nominal performance.
+ *
+ * Return: 0 on success, negative errno on failure.
+ */
+int cppc_get_effective_guaranteed_perf(int cpunum, u64 *guaranteed_perf)
+{
+	struct cppc_perf_caps perf_caps;
+	int ret;
+
+	ret = cppc_get_perf_caps(cpunum, &perf_caps);
+	if (ret)
+		return ret;
+	*guaranteed_perf = perf_caps.guaranteed_perf ?:
+			   perf_caps.nominal_perf;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(cppc_get_effective_guaranteed_perf);
+
 /**
  * cppc_get_epp_perf - Get the epp register value.
  * @cpunum: CPU from which to get epp preference value.
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 8dc22a65e025..8934e48f71a2 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -404,17 +404,15 @@ static void intel_pstate_set_itmt_prio(int cpu)
 
 static int intel_pstate_get_cppc_guaranteed(int cpu)
 {
-	struct cppc_perf_caps cppc_perf;
+	u64 guaranteed_perf;
 	int ret;
 
-	ret = cppc_get_perf_caps(cpu, &cppc_perf);
+	ret = cppc_get_effective_guaranteed_perf(cpu, &guaranteed_perf);
+
 	if (ret)
 		return ret;
 
-	if (cppc_perf.guaranteed_perf)
-		return cppc_perf.guaranteed_perf;
-
-	return cppc_perf.nominal_perf;
+	return guaranteed_perf;
 }
 
 static int intel_pstate_cppc_get_scaling(int cpu)
diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
index d1f02ceec4f9..c02f3bc1fc1a 100644
--- a/include/acpi/cppc_acpi.h
+++ b/include/acpi/cppc_acpi.h
@@ -155,6 +155,7 @@ struct cppc_cpudata {
 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_effective_guaranteed_perf(int cpunum, u64 *guaranteed_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);
@@ -198,6 +199,10 @@ static inline int cppc_get_highest_perf(int cpunum, u64 *highest_perf)
 {
 	return -EOPNOTSUPP;
 }
+static inline int cppc_get_effective_guaranteed_perf(int cpunum, u64 *guaranteed_perf)
+{
+	return -EOPNOTSUPP;
+}
 static inline int cppc_get_perf_ctrs(int cpu, struct cppc_perf_fb_ctrs *perf_fb_ctrs)
 {
 	return -EOPNOTSUPP;
-- 
2.43.0