drivers/thermal/gov_bang_bang.c

   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 }