1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 *  gov_bang_bang.c - A simple thermal throttling governor using hysteresis
  4 *
  5 *  Copyright (C) 2014 Peter Kaestle <peter@piie.net>
  6 *
  7 *  Based on step_wise.c with following Copyrights:
  8 *  Copyright (C) 2012 Intel Corp
  9 *  Copyright (C) 2012 Durgadoss R <durgadoss.r@intel.com>
 10 */
 11
 12#include <linux/thermal.h>
 13
 14#include "thermal_core.h"
 15
 16static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
 17{
 18	int trip_temp, trip_hyst;
 19	struct thermal_instance *instance;
 20
 21	tz->ops->get_trip_temp(tz, trip, &trip_temp);
 22
 23	if (!tz->ops->get_trip_hyst) {
 24		pr_warn_once("Undefined get_trip_hyst for thermal zone %s - "
 25				"running with default hysteresis zero\n", tz->type);
 26		trip_hyst = 0;
 27	} else
 28		tz->ops->get_trip_hyst(tz, trip, &trip_hyst);
 29
 30	dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n",
 31				trip, trip_temp, tz->temperature,
 32				trip_hyst);
 33
 34	list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
 35		if (instance->trip != trip)
 36			continue;
 37
 38		/* in case fan is in initial state, switch the fan off */
 39		if (instance->target == THERMAL_NO_TARGET)
 40			instance->target = 0;
 41
 42		/* in case fan is neither on nor off set the fan to active */
 43		if (instance->target != 0 && instance->target != 1) {
 44			pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
 45					instance->name, instance->target);
 46			instance->target = 1;
 47		}
 48
 49		/*
 50		 * enable fan when temperature exceeds trip_temp and disable
 51		 * the fan in case it falls below trip_temp minus hysteresis
 52		 */
 53		if (instance->target == 0 && tz->temperature >= trip_temp)
 54			instance->target = 1;
 55		else if (instance->target == 1 &&
 56				tz->temperature <= trip_temp - trip_hyst)
 57			instance->target = 0;
 58
 59		dev_dbg(&instance->cdev->device, "target=%d\n",
 60					(int)instance->target);
 61
 62		mutex_lock(&instance->cdev->lock);
 63		instance->cdev->updated = false; /* cdev needs update */
 64		mutex_unlock(&instance->cdev->lock);
 65	}
 66}
 67
 68/**
 69 * bang_bang_control - controls devices associated with the given zone
 70 * @tz: thermal_zone_device
 71 * @trip: the trip point
 72 *
 73 * Regulation Logic: a two point regulation, deliver cooling state depending
 74 * on the previous state shown in this diagram:
 75 *
 76 *                Fan:   OFF    ON
 77 *
 78 *                              |
 79 *                              |
 80 *          trip_temp:    +---->+
 81 *                        |     |        ^
 82 *                        |     |        |
 83 *                        |     |   Temperature
 84 * (trip_temp - hyst):    +<----+
 85 *                        |
 86 *                        |
 87 *                        |
 88 *
 89 *   * If the fan is not running and temperature exceeds trip_temp, the fan
 90 *     gets turned on.
 91 *   * In case the fan is running, temperature must fall below
 92 *     (trip_temp - hyst) so that the fan gets turned off again.
 93 *
 94 */
 95static int bang_bang_control(struct thermal_zone_device *tz, int trip)
 96{
 97	struct thermal_instance *instance;
 98
 99	lockdep_assert_held(&tz->lock);
100
101	thermal_zone_trip_update(tz, trip);
102
103	list_for_each_entry(instance, &tz->thermal_instances, tz_node)
104		thermal_cdev_update(instance->cdev);
105
106	return 0;
107}
108
109static struct thermal_governor thermal_gov_bang_bang = {
110	.name		= "bang_bang",
111	.throttle	= bang_bang_control,
112};
113THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);