drivers: thermal: step_wise: add support for hysteresis

Step wise governor increases the mitigation level when the temperature
goes above a threshold and will decrease the mitigation when the
temperature falls below the threshold. If it were a case, where the
temperature hovers around a threshold, the mitigation will be applied
and removed at every iteration. This reaction to the temperature is
inefficient for performance.

The use of hysteresis temperature could avoid this ping-pong of
mitigation by relaxing the mitigation to happen only when the
temperature goes below this lower hysteresis value.

Signed-off-by: Ram Chandrasekar <[email protected]>
Signed-off-by: Lina Iyer <[email protected]>

drivers: thermal: step_wise: avoid throttling at hysteresis temperature after dropping below it

Signed-off-by: Serge Schneider <[email protected]>

Author: Ram Chandrasekar

drivers/thermal/gov_step_wise.c

@@ -86,22 +86,33 @@ static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip_id
 	struct thermal_instance *instance;
 	bool throttle = false;
 	int old_target;
+	int hyst_temp;
 
 	trend = get_tz_trend(tz, trip_id);
 
-	if (tz->temperature >= trip->temperature) {
-		throttle = true;
-		trace_thermal_zone_trip(tz, trip_id, trip->type);
-	}
+	hyst_temp = trip->temperature - trip->hysteresis;
 
-	dev_dbg(&tz->device, "Trip%d[type=%d,temp=%d]:trend=%d,throttle=%d\n",
-		trip_id, trip->type, trip->temperature, trend, throttle);
+	dev_dbg(&tz->device,
+		"Trip%d[type=%d,temp=%d,hyst=%d]:trend=%d,throttle=%d\n",
+		trip_id, trip->type, trip->temperature, hyst_temp, trend, throttle);
 
 	list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
 		if (instance->trip != trip)
 			continue;
 
 		old_target = instance->target;
+		throttle = false;
+		/*
+		 * Lower the mitigation only if the temperature
+		 * goes below the hysteresis temperature.
+		 */
+		if (tz->temperature >= trip->temperature ||
+		   (tz->temperature >= hyst_temp &&
+		    old_target == instance->upper)) {
+			throttle = true;
+			trace_thermal_zone_trip(tz, trip_id, trip->type);
+		}
+
 		instance->target = get_target_state(instance, trend, throttle);
 		dev_dbg(&instance->cdev->device, "old_target=%d, target=%d\n",
 					old_target, (int)instance->target);