LXR linux/drivers/thermal/gov_bang

   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
  16static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
  17{
  18        int trip_temp, trip_hyst;
  19        struct thermal_instance *instance;
  20
  21        tz->ops->get_trip_temp(tz, trip, &trip_temp);
  22
  23        if (!tz->ops->get_trip_hyst) {
  24                pr_warn_once("Undefined get_trip_hyst for thermal zone %s - "
  25                                "running with default hysteresis zero\n", tz->type);
  26                trip_hyst = 0;
  27        } else
  28                tz->ops->get_trip_hyst(tz, trip, &trip_hyst);
  29
  30        dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n",
  31                                trip, trip_temp, tz->temperature,
  32                                trip_hyst);
  33
  34        mutex_lock(&tz->lock);
  35
  36        list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
  37                if (instance->trip != trip)
  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_temp)
  56                        instance->target = 1;
  57                else if (instance->target == 1 &&
  58                                tz->temperature <= trip_temp - trip_hyst)
  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        mutex_unlock(&tz->lock);
  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 */
  99static int bang_bang_control(struct thermal_zone_device *tz, int trip)
 100{
 101        struct thermal_instance *instance;
 102
 103        thermal_zone_trip_update(tz, trip);
 104
 105        mutex_lock(&tz->lock);
 106
 107        list_for_each_entry(instance, &tz->thermal_instances, tz_node)
 108                thermal_cdev_update(instance->cdev);
 109
 110        mutex_unlock(&tz->lock);
 111
 112        return 0;
 113}
 114
 115static struct thermal_governor thermal_gov_bang_bang = {
 116        .name           = "bang_bang",
 117        .throttle       = bang_bang_control,
 118};
 119THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);
 120