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}
131