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_index)16 static int thermal_zone_trip_update(struct thermal_zone_device *tz, int trip_index)
17 {
18 const struct thermal_trip *trip = &tz->trips[trip_index];
19 struct thermal_instance *instance;
20
21 if (!trip->hysteresis)
22 dev_info_once(&tz->device,
23 "Zero hysteresis value for thermal zone %s\n", tz->type);
24
25 dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n",
26 trip_index, trip->temperature, tz->temperature,
27 trip->hysteresis);
28
29 list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
30 if (instance->trip != trip)
31 continue;
32
33 /* in case fan is in initial state, switch the fan off */
34 if (instance->target == THERMAL_NO_TARGET)
35 instance->target = 0;
36
37 /* in case fan is neither on nor off set the fan to active */
38 if (instance->target != 0 && instance->target != 1) {
39 pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
40 instance->name, instance->target);
41 instance->target = 1;
42 }
43
44 /*
45 * enable fan when temperature exceeds trip_temp and disable
46 * the fan in case it falls below trip_temp minus hysteresis
47 */
48 if (instance->target == 0 && tz->temperature >= trip->temperature)
49 instance->target = 1;
50 else if (instance->target == 1 &&
51 tz->temperature <= trip->temperature - trip->hysteresis)
52 instance->target = 0;
53
54 dev_dbg(&instance->cdev->device, "target=%d\n",
55 (int)instance->target);
56
57 mutex_lock(&instance->cdev->lock);
58 instance->cdev->updated = false; /* cdev needs update */
59 mutex_unlock(&instance->cdev->lock);
60 }
61
62 return 0;
63 }
64
65 /**
66 * bang_bang_control - controls devices associated with the given zone
67 * @tz: thermal_zone_device
68 * @trip: the trip point
69 *
70 * Regulation Logic: a two point regulation, deliver cooling state depending
71 * on the previous state shown in this diagram:
72 *
73 * Fan: OFF ON
74 *
75 * |
76 * |
77 * trip_temp: +---->+
78 * | | ^
79 * | | |
80 * | | Temperature
81 * (trip_temp - hyst): +<----+
82 * |
83 * |
84 * |
85 *
86 * * If the fan is not running and temperature exceeds trip_temp, the fan
87 * gets turned on.
88 * * In case the fan is running, temperature must fall below
89 * (trip_temp - hyst) so that the fan gets turned off again.
90 *
91 */
bang_bang_control(struct thermal_zone_device * tz,int trip)92 static int bang_bang_control(struct thermal_zone_device *tz, int trip)
93 {
94 struct thermal_instance *instance;
95 int ret;
96
97 lockdep_assert_held(&tz->lock);
98
99 ret = thermal_zone_trip_update(tz, trip);
100 if (ret)
101 return ret;
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