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 
26 static 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  */
101 static 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 
117 static struct thermal_governor thermal_gov_bang_bang = {
118 	.name		= "bang_bang",
119 	.throttle	= bang_bang_control,
120 };
121 
122 int thermal_gov_bang_bang_register(void)
123 {
124 	return thermal_register_governor(&thermal_gov_bang_bang);
125 }
126 
127 void thermal_gov_bang_bang_unregister(void)
128 {
129 	thermal_unregister_governor(&thermal_gov_bang_bang);
130 }
131