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 <rkumbako@codeaurora.org>
Signed-off-by: Lina Iyer <ilina@codeaurora.org>

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

Signed-off-by: Serge Schneider <serge@raspberrypi.org>

Fix hysteresis support in gov_step_wise.c

Directly get hyst value instead of going through an
optional and, now, unimplemented function.

Signed-off-by: Jürgen Kreileder <jk@blackdown.de>

Author: Ram Chandrasekar

drivers/thermal/gov_step_wise.c

@@ -17,13 +17,13 @@
 #include "thermal_core.h"
 
 /*
- * If the temperature is higher than a trip point,
+ * If the temperature is higher than a hysteresis temperature,
  *    a. if the trend is THERMAL_TREND_RAISING, use higher cooling
  *       state for this trip point
  *    b. if the trend is THERMAL_TREND_DROPPING, use a lower cooling state
  *       for this trip point, but keep the cooling state above the applicable
  *       minimum
- * If the temperature is lower than a trip point,
+ * If the temperature is lower than a hysteresis temperature,
  *    a. if the trend is THERMAL_TREND_RAISING, do nothing
  *    b. if the trend is THERMAL_TREND_DROPPING, use the minimum applicable
  *       cooling state for this trip point, or if the cooling state already
@@ -82,22 +82,37 @@ static void thermal_zone_trip_update(struct thermal_zone_device *tz,
 				     const struct thermal_trip_desc *td,
 				     int trip_threshold)
 {
-	bool throttle = tz->temperature >= trip_threshold;
 	const struct thermal_trip *trip = &td->trip;
+	int hyst_temp = trip->temperature - trip->hysteresis;
+	bool throttle = tz->temperature >= hyst_temp;
 	enum thermal_trend trend = get_tz_trend(tz, trip);
 	int trip_id = thermal_zone_trip_id(tz, trip);
 	struct thermal_instance *instance;
 
 	if (throttle)
 		trace_thermal_zone_trip(tz, trip_id, trip->type);
 
-	dev_dbg(&tz->device, "Trip%d[type=%d,temp=%d]:trend=%d,throttle=%d\n",
-		trip_id, trip->type, trip_threshold, 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, &td->thermal_instances, trip_node) {
 		int old_target;
 
 		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=%ld\n",