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// SPDX-License-Identifier: GPL-2.0-only
/*
* gov_bang_bang.c - A simple thermal throttling governor using hysteresis
*
* Copyright (C) 2014 Peter Kaestle <peter@piie.net>
*
* Based on step_wise.c with following Copyrights:
* Copyright (C) 2012 Intel Corp
* Copyright (C) 2012 Durgadoss R <durgadoss.r@intel.com>
*/
#include <linux/thermal.h>
#include "thermal_core.h"
static int thermal_zone_trip_update(struct thermal_zone_device *tz, int trip_id)
{
struct thermal_trip trip;
struct thermal_instance *instance;
int ret;
ret = __thermal_zone_get_trip(tz, trip_id, &trip);
if (ret) {
pr_warn_once("Failed to retrieve trip point %d\n", trip_id);
return ret;
}
if (!trip.hysteresis)
dev_info_once(&tz->device,
"Zero hysteresis value for thermal zone %s\n", tz->type);
dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n",
trip_id, trip.temperature, tz->temperature,
trip.hysteresis);
list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
if (instance->trip != trip_id)
continue;
/* in case fan is in initial state, switch the fan off */
if (instance->target == THERMAL_NO_TARGET)
instance->target = 0;
/* in case fan is neither on nor off set the fan to active */
if (instance->target != 0 && instance->target != 1) {
pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
instance->name, instance->target);
instance->target = 1;
}
/*
* enable fan when temperature exceeds trip_temp and disable
* the fan in case it falls below trip_temp minus hysteresis
*/
if (instance->target == 0 && tz->temperature >= trip.temperature)
instance->target = 1;
else if (instance->target == 1 &&
tz->temperature <= trip.temperature - trip.hysteresis)
instance->target = 0;
dev_dbg(&instance->cdev->device, "target=%d\n",
(int)instance->target);
mutex_lock(&instance->cdev->lock);
instance->cdev->updated = false; /* cdev needs update */
mutex_unlock(&instance->cdev->lock);
}
return 0;
}
/**
* bang_bang_control - controls devices associated with the given zone
* @tz: thermal_zone_device
* @trip: the trip point
*
* Regulation Logic: a two point regulation, deliver cooling state depending
* on the previous state shown in this diagram:
*
* Fan: OFF ON
*
* |
* |
* trip_temp: +---->+
* | | ^
* | | |
* | | Temperature
* (trip_temp - hyst): +<----+
* |
* |
* |
*
* * If the fan is not running and temperature exceeds trip_temp, the fan
* gets turned on.
* * In case the fan is running, temperature must fall below
* (trip_temp - hyst) so that the fan gets turned off again.
*
*/
static int bang_bang_control(struct thermal_zone_device *tz, int trip)
{
struct thermal_instance *instance;
int ret;
lockdep_assert_held(&tz->lock);
ret = thermal_zone_trip_update(tz, trip);
if (ret)
return ret;
list_for_each_entry(instance, &tz->thermal_instances, tz_node)
thermal_cdev_update(instance->cdev);
return 0;
}
static struct thermal_governor thermal_gov_bang_bang = {
.name = "bang_bang",
.throttle = bang_bang_control,
};
THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);
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