1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * gov_bang_bang.c - A simple thermal throttling governor using hysteresis
4 *
5 * Copyright (C) 2014 Peter Kaestle <peter@piie.net>
6 *
7 * Based on step_wise.c with following Copyrights:
8 * Copyright (C) 2012 Intel Corp
9 * Copyright (C) 2012 Durgadoss R <durgadoss.r@intel.com>
10 */
11
12 #include <linux/thermal.h>
13
14 #include "thermal_core.h"
15
thermal_zone_trip_update(struct thermal_zone_device * tz,int trip)16 static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
17 {
18 int trip_temp, trip_hyst;
19 struct thermal_instance *instance;
20
21 tz->ops->get_trip_temp(tz, trip, &trip_temp);
22
23 if (!tz->ops->get_trip_hyst) {
24 pr_warn_once("Undefined get_trip_hyst for thermal zone %s - "
25 "running with default hysteresis zero\n", tz->type);
26 trip_hyst = 0;
27 } else
28 tz->ops->get_trip_hyst(tz, trip, &trip_hyst);
29
30 dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n",
31 trip, trip_temp, tz->temperature,
32 trip_hyst);
33
34 list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
35 if (instance->trip != trip)
36 continue;
37
38 /* in case fan is in initial state, switch the fan off */
39 if (instance->target == THERMAL_NO_TARGET)
40 instance->target = 0;
41
42 /* in case fan is neither on nor off set the fan to active */
43 if (instance->target != 0 && instance->target != 1) {
44 pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
45 instance->name, instance->target);
46 instance->target = 1;
47 }
48
49 /*
50 * enable fan when temperature exceeds trip_temp and disable
51 * the fan in case it falls below trip_temp minus hysteresis
52 */
53 if (instance->target == 0 && tz->temperature >= trip_temp)
54 instance->target = 1;
55 else if (instance->target == 1 &&
56 tz->temperature <= trip_temp - trip_hyst)
57 instance->target = 0;
58
59 dev_dbg(&instance->cdev->device, "target=%d\n",
60 (int)instance->target);
61
62 mutex_lock(&instance->cdev->lock);
63 instance->cdev->updated = false; /* cdev needs update */
64 mutex_unlock(&instance->cdev->lock);
65 }
66 }
67
68 /**
69 * bang_bang_control - controls devices associated with the given zone
70 * @tz: thermal_zone_device
71 * @trip: the trip point
72 *
73 * Regulation Logic: a two point regulation, deliver cooling state depending
74 * on the previous state shown in this diagram:
75 *
76 * Fan: OFF ON
77 *
78 * |
79 * |
80 * trip_temp: +---->+
81 * | | ^
82 * | | |
83 * | | Temperature
84 * (trip_temp - hyst): +<----+
85 * |
86 * |
87 * |
88 *
89 * * If the fan is not running and temperature exceeds trip_temp, the fan
90 * gets turned on.
91 * * In case the fan is running, temperature must fall below
92 * (trip_temp - hyst) so that the fan gets turned off again.
93 *
94 */
bang_bang_control(struct thermal_zone_device * tz,int trip)95 static int bang_bang_control(struct thermal_zone_device *tz, int trip)
96 {
97 struct thermal_instance *instance;
98
99 lockdep_assert_held(&tz->lock);
100
101 thermal_zone_trip_update(tz, trip);
102
103 list_for_each_entry(instance, &tz->thermal_instances, tz_node)
104 thermal_cdev_update(instance->cdev);
105
106 return 0;
107 }
108
109 static struct thermal_governor thermal_gov_bang_bang = {
110 .name = "bang_bang",
111 .throttle = bang_bang_control,
112 };
113 THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);
114