Revert "Revert "drivers: thermal: step_wise: add support for hysteresis""

This reverts commit 0e2d9b4.

Author: popcornmix

drivers/thermal/gov_step_wise.c

@@ -17,16 +17,16 @@
 #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 lower cooling
- *       state for this trip point, if the cooling state already
+ *    b. if the trend is THERMAL_TREND_DROPPING, use the minimum applicable
+ *       cooling state for this trip point, or if the cooling state already
  *       equals lower limit, deactivate the thermal instance
  */
 static unsigned long get_target_state(struct thermal_instance *instance,
@@ -83,23 +83,36 @@ static void thermal_zone_trip_update(struct thermal_zone_device *tz,
 				     int 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;
-	bool throttle = false;
 
-	if (tz->temperature >= trip_threshold) {
-		throttle = true;
+	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",