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 
33 	if (!tz->ops->get_trip_hyst) {
34 		pr_warn_once("Undefined get_trip_hyst for thermal zone %s - "
35 				"running with default hysteresis zero\n", tz->type);
36 		trip_hyst = 0;
37 	} else
38 		tz->ops->get_trip_hyst(tz, trip, &trip_hyst);
39 
40 	dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n",
41 				trip, trip_temp, tz->temperature,
42 				trip_hyst);
43 
44 	mutex_lock(&tz->lock);
45 
46 	list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
47 		if (instance->trip != trip)
48 			continue;
49 
50 		/* in case fan is in initial state, switch the fan off */
51 		if (instance->target == THERMAL_NO_TARGET)
52 			instance->target = 0;
53 
54 		/* in case fan is neither on nor off set the fan to active */
55 		if (instance->target != 0 && instance->target != 1) {
56 			pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
57 					instance->name, instance->target);
58 			instance->target = 1;
59 		}
60 
61 		/*
62 		 * enable fan when temperature exceeds trip_temp and disable
63 		 * the fan in case it falls below trip_temp minus hysteresis
64 		 */
65 		if (instance->target == 0 && tz->temperature >= trip_temp)
66 			instance->target = 1;
67 		else if (instance->target == 1 &&
68 				tz->temperature < trip_temp - trip_hyst)
69 			instance->target = 0;
70 
71 		dev_dbg(&instance->cdev->device, "target=%d\n",
72 					(int)instance->target);
73 
74 		instance->cdev->updated = false; /* cdev needs update */
75 	}
76 
77 	mutex_unlock(&tz->lock);
78 }
79 
80 /**
81  * bang_bang_control - controls devices associated with the given zone
82  * @tz - thermal_zone_device
83  * @trip - the trip point
84  *
85  * Regulation Logic: a two point regulation, deliver cooling state depending
86  * on the previous state shown in this diagram:
87  *
88  *                Fan:   OFF    ON
89  *
90  *                              |
91  *                              |
92  *          trip_temp:    +---->+
93  *                        |     |        ^
94  *                        |     |        |
95  *                        |     |   Temperature
96  * (trip_temp - hyst):    +<----+
97  *                        |
98  *                        |
99  *                        |
100  *
101  *   * If the fan is not running and temperature exceeds trip_temp, the fan
102  *     gets turned on.
103  *   * In case the fan is running, temperature must fall below
104  *     (trip_temp - hyst) so that the fan gets turned off again.
105  *
106  */
107 static int bang_bang_control(struct thermal_zone_device *tz, int trip)
108 {
109 	struct thermal_instance *instance;
110 
111 	thermal_zone_trip_update(tz, trip);
112 
113 	mutex_lock(&tz->lock);
114 
115 	list_for_each_entry(instance, &tz->thermal_instances, tz_node)
116 		thermal_cdev_update(instance->cdev);
117 
118 	mutex_unlock(&tz->lock);
119 
120 	return 0;
121 }
122 
123 static struct thermal_governor thermal_gov_bang_bang = {
124 	.name		= "bang_bang",
125 	.throttle	= bang_bang_control,
126 };
127 
128 int thermal_gov_bang_bang_register(void)
129 {
130 	return thermal_register_governor(&thermal_gov_bang_bang);
131 }
132 
133 void thermal_gov_bang_bang_unregister(void)
134 {
135 	thermal_unregister_governor(&thermal_gov_bang_bang);
136 }
137