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 16 static int thermal_zone_trip_update(struct thermal_zone_device *tz, 17 const struct thermal_trip *trip) 18 { 19 int trip_index = thermal_zone_trip_id(tz, trip); 20 struct thermal_instance *instance; 21 22 if (!trip->hysteresis) 23 dev_info_once(&tz->device, 24 "Zero hysteresis value for thermal zone %s\n", tz->type); 25 26 dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n", 27 trip_index, trip->temperature, tz->temperature, 28 trip->hysteresis); 29 30 list_for_each_entry(instance, &tz->thermal_instances, tz_node) { 31 if (instance->trip != trip) 32 continue; 33 34 /* in case fan is in initial state, switch the fan off */ 35 if (instance->target == THERMAL_NO_TARGET) 36 instance->target = 0; 37 38 /* in case fan is neither on nor off set the fan to active */ 39 if (instance->target != 0 && instance->target != 1) { 40 pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n", 41 instance->name, instance->target); 42 instance->target = 1; 43 } 44 45 /* 46 * enable fan when temperature exceeds trip_temp and disable 47 * the fan in case it falls below trip_temp minus hysteresis 48 */ 49 if (instance->target == 0 && tz->temperature >= trip->temperature) 50 instance->target = 1; 51 else if (instance->target == 1 && 52 tz->temperature <= trip->temperature - trip->hysteresis) 53 instance->target = 0; 54 55 dev_dbg(&instance->cdev->device, "target=%d\n", 56 (int)instance->target); 57 58 mutex_lock(&instance->cdev->lock); 59 instance->cdev->updated = false; /* cdev needs update */ 60 mutex_unlock(&instance->cdev->lock); 61 } 62 63 return 0; 64 } 65 66 /** 67 * bang_bang_control - controls devices associated with the given zone 68 * @tz: thermal_zone_device 69 * @trip: the trip point 70 * 71 * Regulation Logic: a two point regulation, deliver cooling state depending 72 * on the previous state shown in this diagram: 73 * 74 * Fan: OFF ON 75 * 76 * | 77 * | 78 * trip_temp: +---->+ 79 * | | ^ 80 * | | | 81 * | | Temperature 82 * (trip_temp - hyst): +<----+ 83 * | 84 * | 85 * | 86 * 87 * * If the fan is not running and temperature exceeds trip_temp, the fan 88 * gets turned on. 89 * * In case the fan is running, temperature must fall below 90 * (trip_temp - hyst) so that the fan gets turned off again. 91 * 92 */ 93 static int bang_bang_control(struct thermal_zone_device *tz, 94 const struct thermal_trip *trip) 95 { 96 struct thermal_instance *instance; 97 int ret; 98 99 lockdep_assert_held(&tz->lock); 100 101 ret = thermal_zone_trip_update(tz, trip); 102 if (ret) 103 return ret; 104 105 list_for_each_entry(instance, &tz->thermal_instances, tz_node) 106 thermal_cdev_update(instance->cdev); 107 108 return 0; 109 } 110 111 static struct thermal_governor thermal_gov_bang_bang = { 112 .name = "bang_bang", 113 .throttle = bang_bang_control, 114 }; 115 THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang); 116