1/*
  2 *  gov_bang_bang.c - A simple thermal throttling governor using hysteresis
  3 *
  4 *  Copyright (C) 2014 Peter Feuerer <peter@piie.net>
  5 *
  6 *  Based on step_wise.c with following Copyrights:
  7 *  Copyright (C) 2012 Intel Corp
  8 *  Copyright (C) 2012 Durgadoss R <durgadoss.r@intel.com>
  9 *
 10 *
 11 * This program is free software; you can redistribute it and/or modify
 12 * it under the terms of the GNU General Public License as published by
 13 * the Free Software Foundation, version 2.
 14 *
 15 * This program is distributed in the hope that it will be useful,
 16 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 17 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
 18 * the GNU General Public License for more details.
 19 *
 20 */
 21
 22#include <linux/thermal.h>
 23
 24#include "thermal_core.h"
 25
 26static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
 27{
 28	int trip_temp, trip_hyst;
 29	struct thermal_instance *instance;
 30
 31	tz->ops->get_trip_temp(tz, trip, &trip_temp);
 32	tz->ops->get_trip_hyst(tz, trip, &trip_hyst);
 33
 34	dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n",
 35				trip, trip_temp, tz->temperature,
 36				trip_hyst);
 37
 38	mutex_lock(&tz->lock);
 39
 40	list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
 41		if (instance->trip != trip)
 42			continue;
 43
 44		/* in case fan is in initial state, switch the fan off */
 45		if (instance->target == THERMAL_NO_TARGET)
 46			instance->target = 0;
 47
 48		/* in case fan is neither on nor off set the fan to active */
 49		if (instance->target != 0 && instance->target != 1) {
 50			pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
 51					instance->name, instance->target);
 52			instance->target = 1;
 53		}
 54
 55		/*
 56		 * enable fan when temperature exceeds trip_temp and disable
 57		 * the fan in case it falls below trip_temp minus hysteresis
 58		 */
 59		if (instance->target == 0 && tz->temperature >= trip_temp)
 60			instance->target = 1;
 61		else if (instance->target == 1 &&
 62				tz->temperature < trip_temp - trip_hyst)
 63			instance->target = 0;
 64
 65		dev_dbg(&instance->cdev->device, "target=%d\n",
 66					(int)instance->target);
 67
 68		instance->cdev->updated = false; /* cdev needs update */
 69	}
 70
 71	mutex_unlock(&tz->lock);
 72}
 73
 74/**
 75 * bang_bang_control - controls devices associated with the given zone
 76 * @tz - thermal_zone_device
 77 * @trip - the trip point
 78 *
 79 * Regulation Logic: a two point regulation, deliver cooling state depending
 80 * on the previous state shown in this diagram:
 81 *
 82 *                Fan:   OFF    ON
 83 *
 84 *                              |
 85 *                              |
 86 *          trip_temp:    +---->+
 87 *                        |     |        ^
 88 *                        |     |        |
 89 *                        |     |   Temperature
 90 * (trip_temp - hyst):    +<----+
 91 *                        |
 92 *                        |
 93 *                        |
 94 *
 95 *   * If the fan is not running and temperature exceeds trip_temp, the fan
 96 *     gets turned on.
 97 *   * In case the fan is running, temperature must fall below
 98 *     (trip_temp - hyst) so that the fan gets turned off again.
 99 *
100 */
101static int bang_bang_control(struct thermal_zone_device *tz, int trip)
102{
103	struct thermal_instance *instance;
104
105	thermal_zone_trip_update(tz, trip);
106
107	mutex_lock(&tz->lock);
108
109	list_for_each_entry(instance, &tz->thermal_instances, tz_node)
110		thermal_cdev_update(instance->cdev);
111
112	mutex_unlock(&tz->lock);
113
114	return 0;
115}
116
117static struct thermal_governor thermal_gov_bang_bang = {
118	.name		= "bang_bang",
119	.throttle	= bang_bang_control,
120};
121
122int thermal_gov_bang_bang_register(void)
123{
124	return thermal_register_governor(&thermal_gov_bang_bang);
125}
126
127void thermal_gov_bang_bang_unregister(void)
128{
129	thermal_unregister_governor(&thermal_gov_bang_bang);
130}