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_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  */
  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);