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 	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  */
102 static 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 
118 static struct thermal_governor thermal_gov_bang_bang = {
119 	.name		= "bang_bang",
120 	.throttle	= bang_bang_control,
121 };
122 
123 int thermal_gov_bang_bang_register(void)
124 {
125 	return thermal_register_governor(&thermal_gov_bang_bang);
126 }
127 
128 void thermal_gov_bang_bang_unregister(void)
129 {
130 	thermal_unregister_governor(&thermal_gov_bang_bang);
131 }
132