drivers/thermal/gov_bang_bang.c

   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, int trip_id)
  17 {
  18         struct thermal_trip trip;
  19         struct thermal_instance *instance;
  20         int ret;
  21
  22         ret = __thermal_zone_get_trip(tz, trip_id, &trip);
  23         if (ret) {
  24                 pr_warn_once("Failed to retrieve trip point %d\n", trip_id);
  25                 return ret;
  26         }
  27
  28         if (!trip.hysteresis)
  29                 dev_info_once(&tz->device,
  30                               "Zero hysteresis value for thermal zone %s\n", tz->type);
  31
  32         dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n",
  33                                 trip_id, trip.temperature, tz->temperature,
  34                                 trip.hysteresis);
  35
  36         list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
  37                 if (instance->trip != trip_id)
  38                         continue;
  39
  40                 /* in case fan is in initial state, switch the fan off */
  41                 if (instance->target == THERMAL_NO_TARGET)
  42                         instance->target = 0;
  43
  44                 /* in case fan is neither on nor off set the fan to active */
  45                 if (instance->target != 0 && instance->target != 1) {
  46                         pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
  47                                         instance->name, instance->target);
  48                         instance->target = 1;
  49                 }
  50
  51                 /*
  52                  * enable fan when temperature exceeds trip_temp and disable
  53                  * the fan in case it falls below trip_temp minus hysteresis
  54                  */
  55                 if (instance->target == 0 && tz->temperature >= trip.temperature)
  56                         instance->target = 1;
  57                 else if (instance->target == 1 &&
  58                          tz->temperature <= trip.temperature - trip.hysteresis)
  59                         instance->target = 0;
  60
  61                 dev_dbg(&instance->cdev->device, "target=%d\n",
  62                                         (int)instance->target);
  63
  64                 mutex_lock(&instance->cdev->lock);
  65                 instance->cdev->updated = false; /* cdev needs update */
  66                 mutex_unlock(&instance->cdev->lock);
  67         }
  68
  69         return 0;
  70 }
  71
  72 /**
  73  * bang_bang_control - controls devices associated with the given zone
  74  * @tz: thermal_zone_device
  75  * @trip: the trip point
  76  *
  77  * Regulation Logic: a two point regulation, deliver cooling state depending
  78  * on the previous state shown in this diagram:
  79  *
  80  *                Fan:   OFF    ON
  81  *
  82  *                              |
  83  *                              |
  84  *          trip_temp:    +---->+
  85  *                        |     |        ^
  86  *                        |     |        |
  87  *                        |     |   Temperature
  88  * (trip_temp - hyst):    +<----+
  89  *                        |
  90  *                        |
  91  *                        |
  92  *
  93  *   * If the fan is not running and temperature exceeds trip_temp, the fan
  94  *     gets turned on.
  95  *   * In case the fan is running, temperature must fall below
  96  *     (trip_temp - hyst) so that the fan gets turned off again.
  97  *
  98  */
  99 static int bang_bang_control(struct thermal_zone_device *tz, int trip)
 100 {
 101         struct thermal_instance *instance;
 102         int ret;
 103
 104         lockdep_assert_held(&tz->lock);
 105
 106         ret = thermal_zone_trip_update(tz, trip);
 107         if (ret)
 108                 return ret;
 109
 110         list_for_each_entry(instance, &tz->thermal_instances, tz_node)
 111                 thermal_cdev_update(instance->cdev);
 112
 113         return 0;
 114 }
 115
 116 static struct thermal_governor thermal_gov_bang_bang = {
 117         .name           = "bang_bang",
 118         .throttle       = bang_bang_control,
 119 };
 120 THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);