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 int thermal_zone_trip_update(struct thermal_zone_device *tz,
 17				    const struct thermal_trip *trip)
 18{
 19	int trip_index = thermal_zone_trip_id(tz, trip);
 20	struct thermal_instance *instance;
 21
 22	if (!trip->hysteresis)
 23		dev_info_once(&tz->device,
 24			      "Zero hysteresis value for thermal zone %s\n", tz->type);
 25
 26	dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n",
 27				trip_index, trip->temperature, tz->temperature,
 28				trip->hysteresis);
 29
 30	list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
 31		if (instance->trip != trip)
 32			continue;
 33
 34		/* in case fan is in initial state, switch the fan off */
 35		if (instance->target == THERMAL_NO_TARGET)
 36			instance->target = 0;
 37
 38		/* in case fan is neither on nor off set the fan to active */
 39		if (instance->target != 0 && instance->target != 1) {
 40			pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
 41					instance->name, instance->target);
 42			instance->target = 1;
 43		}
 44
 45		/*
 46		 * enable fan when temperature exceeds trip_temp and disable
 47		 * the fan in case it falls below trip_temp minus hysteresis
 48		 */
 49		if (instance->target == 0 && tz->temperature >= trip->temperature)
 50			instance->target = 1;
 51		else if (instance->target == 1 &&
 52			 tz->temperature < trip->temperature - trip->hysteresis)
 53			instance->target = 0;
 54
 55		dev_dbg(&instance->cdev->device, "target=%d\n",
 56					(int)instance->target);
 57
 58		mutex_lock(&instance->cdev->lock);
 59		instance->cdev->updated = false; /* cdev needs update */
 60		mutex_unlock(&instance->cdev->lock);
 61	}
 62
 63	return 0;
 64}
 65
 66/**
 67 * bang_bang_control - controls devices associated with the given zone
 68 * @tz: thermal_zone_device
 69 * @trip: the trip point
 70 *
 71 * Regulation Logic: a two point regulation, deliver cooling state depending
 72 * on the previous state shown in this diagram:
 73 *
 74 *                Fan:   OFF    ON
 75 *
 76 *                              |
 77 *                              |
 78 *          trip_temp:    +---->+
 79 *                        |     |        ^
 80 *                        |     |        |
 81 *                        |     |   Temperature
 82 * (trip_temp - hyst):    +<----+
 83 *                        |
 84 *                        |
 85 *                        |
 86 *
 87 *   * If the fan is not running and temperature exceeds trip_temp, the fan
 88 *     gets turned on.
 89 *   * In case the fan is running, temperature must fall below
 90 *     (trip_temp - hyst) so that the fan gets turned off again.
 91 *
 92 */
 93static int bang_bang_control(struct thermal_zone_device *tz,
 94			     const struct thermal_trip *trip)
 95{
 96	struct thermal_instance *instance;
 97	int ret;
 98
 99	lockdep_assert_held(&tz->lock);
100
101	ret = thermal_zone_trip_update(tz, trip);
102	if (ret)
103		return ret;
104
105	list_for_each_entry(instance, &tz->thermal_instances, tz_node)
106		thermal_cdev_update(instance->cdev);
107
108	return 0;
109}
110
111static struct thermal_governor thermal_gov_bang_bang = {
112	.name		= "bang_bang",
113	.throttle	= bang_bang_control,
114};
115THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);