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 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 */
 64static 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
 81static 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
113static 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
124static 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};
130THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);