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	long trip_temp;
29	unsigned long trip_hyst;
30	struct thermal_instance *instance;
31
32	tz->ops->get_trip_temp(tz, trip, &trip_temp);
33	tz->ops->get_trip_hyst(tz, trip, &trip_hyst);
34
35	dev_dbg(&tz->device, "Trip%d[temp=%ld]:temp=%d:hyst=%ld\n",
36				trip, trip_temp, tz->temperature,
37				trip_hyst);
38
39	mutex_lock(&tz->lock);
40
41	list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
42		if (instance->trip != trip)
43			continue;
44
45		/* in case fan is in initial state, switch the fan off */
46		if (instance->target == THERMAL_NO_TARGET)
47			instance->target = 0;
48
49		/* in case fan is neither on nor off set the fan to active */
50		if (instance->target != 0 && instance->target != 1) {
51			pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
52					instance->name, instance->target);
53			instance->target = 1;
54		}
55
56		/*
57		 * enable fan when temperature exceeds trip_temp and disable
58		 * the fan in case it falls below trip_temp minus hysteresis
59		 */
60		if (instance->target == 0 && tz->temperature >= trip_temp)
61			instance->target = 1;
62		else if (instance->target == 1 &&
63				tz->temperature < trip_temp - trip_hyst)
64			instance->target = 0;
65
66		dev_dbg(&instance->cdev->device, "target=%d\n",
67					(int)instance->target);
68
69		instance->cdev->updated = false; /* cdev needs update */
70	}
71
72	mutex_unlock(&tz->lock);
73}
74
75/**
76 * bang_bang_control - controls devices associated with the given zone
77 * @tz - thermal_zone_device
78 * @trip - the trip point
79 *
80 * Regulation Logic: a two point regulation, deliver cooling state depending
81 * on the previous state shown in this diagram:
82 *
83 *                Fan:   OFF    ON
84 *
85 *                              |
86 *                              |
87 *          trip_temp:    +---->+
88 *                        |     |        ^
89 *                        |     |        |
90 *                        |     |   Temperature
91 * (trip_temp - hyst):    +<----+
92 *                        |
93 *                        |
94 *                        |
95 *
96 *   * If the fan is not running and temperature exceeds trip_temp, the fan
97 *     gets turned on.
98 *   * In case the fan is running, temperature must fall below
99 *     (trip_temp - hyst) so that the fan gets turned off again.
100 *
101 */
102static int bang_bang_control(struct thermal_zone_device *tz, int trip)
103{
104	struct thermal_instance *instance;
105
106	thermal_zone_trip_update(tz, trip);
107
108	mutex_lock(&tz->lock);
109
110	list_for_each_entry(instance, &tz->thermal_instances, tz_node)
111		thermal_cdev_update(instance->cdev);
112
113	mutex_unlock(&tz->lock);
114
115	return 0;
116}
117
118static struct thermal_governor thermal_gov_bang_bang = {
119	.name		= "bang_bang",
120	.throttle	= bang_bang_control,
121};
122
123int thermal_gov_bang_bang_register(void)
124{
125	return thermal_register_governor(&thermal_gov_bang_bang);
126}
127
128void thermal_gov_bang_bang_unregister(void)
129{
130	thermal_unregister_governor(&thermal_gov_bang_bang);
131}
132