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 void bang_bang_set_instance_target(struct thermal_instance *instance,
  17                                           unsigned int target)
  18 {
  19         if (instance->target != 0 && instance->target != 1 &&
  20             instance->target != THERMAL_NO_TARGET)
  21                 pr_debug("Unexpected state %ld of thermal instance %s in bang-bang\n",
  22                          instance->target, instance->name);
  23
  24         /*
  25          * Enable the fan when the trip is crossed on the way up and disable it
  26          * when the trip is crossed on the way down.
  27          */
  28         instance->target = target;
  29         instance->initialized = true;
  30
  31         dev_dbg(&instance->cdev->device, "target=%ld\n", instance->target);
  32
  33         thermal_cdev_update_nocheck(instance->cdev);
  34 }
  35
  36 /**
  37  * bang_bang_control - controls devices associated with the given zone
  38  * @tz: thermal_zone_device
  39  * @trip: the trip point
  40  * @crossed_up: whether or not the trip has been crossed on the way up
  41  *
  42  * Regulation Logic: a two point regulation, deliver cooling state depending
  43  * on the previous state shown in this diagram:
  44  *
  45  *                Fan:   OFF    ON
  46  *
  47  *                              |
  48  *                              |
  49  *          trip_temp:    +---->+
  50  *                        |     |        ^
  51  *                        |     |        |
  52  *                        |     |   Temperature
  53  * (trip_temp - hyst):    +<----+
  54  *                        |
  55  *                        |
  56  *                        |
  57  *
  58  *   * If the fan is not running and temperature exceeds trip_temp, the fan
  59  *     gets turned on.
  60  *   * In case the fan is running, temperature must fall below
  61  *     (trip_temp - hyst) so that the fan gets turned off again.
  62  *
  63  */
  64 static void bang_bang_control(struct thermal_zone_device *tz,
  65                               const struct thermal_trip *trip,
  66                               bool crossed_up)
  67 {
  68         const struct thermal_trip_desc *td = trip_to_trip_desc(trip);
  69         struct thermal_instance *instance;
  70
  71         lockdep_assert_held(&tz->lock);
  72
  73         dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n",
  74                 thermal_zone_trip_id(tz, trip), trip->temperature,
  75                 tz->temperature, trip->hysteresis);
  76
  77         list_for_each_entry(instance, &td->thermal_instances, trip_node)
  78                 bang_bang_set_instance_target(instance, crossed_up);
  79 }
  80
  81 static void bang_bang_manage(struct thermal_zone_device *tz)
  82 {
  83         const struct thermal_trip_desc *td;
  84         struct thermal_instance *instance;
  85
  86         /* If the code below has run already, nothing needs to be done. */
  87         if (tz->governor_data)
  88                 return;
  89
  90         for_each_trip_desc(tz, td) {
  91                 const struct thermal_trip *trip = &td->trip;
  92                 bool turn_on;
  93
  94                 if (trip->temperature == THERMAL_TEMP_INVALID ||
  95                     trip->type == THERMAL_TRIP_CRITICAL ||
  96                     trip->type == THERMAL_TRIP_HOT)
  97                         continue;
  98
  99                 /*
 100                  * Adjust the target states for uninitialized thermal instances
 101                  * to the thermal zone temperature and the trip point threshold.
 102                  */
 103                 turn_on = tz->temperature >= td->threshold;
 104                 list_for_each_entry(instance, &td->thermal_instances, trip_node) {
 105                         if (!instance->initialized)
 106                                 bang_bang_set_instance_target(instance, turn_on);
 107                 }
 108         }
 109
 110         tz->governor_data = (void *)true;
 111 }
 112
 113 static void bang_bang_update_tz(struct thermal_zone_device *tz,
 114                                 enum thermal_notify_event reason)
 115 {
 116         /*
 117          * Let bang_bang_manage() know that it needs to walk trips after binding
 118          * a new cdev and after system resume.
 119          */
 120         if (reason == THERMAL_TZ_BIND_CDEV || reason == THERMAL_TZ_RESUME)
 121                 tz->governor_data = NULL;
 122 }
 123
 124 static struct thermal_governor thermal_gov_bang_bang = {
 125         .name           = "bang_bang",
 126         .trip_crossed   = bang_bang_control,
 127         .manage         = bang_bang_manage,
 128         .update_tz      = bang_bang_update_tz,
 129 };
 130 THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);