Commit f9df89d8 authored by Eduardo Valentin's avatar Eduardo Valentin Committed by Eduardo Valentin

thermal: introduce clock cooling device

This patch introduces a new thermal cooling device based on common clock
framework. The original motivation to write this cooling device is to be
able to cool down thermal zones using clocks that feed co-processors, such
as GPUs, DSPs, Image Processing Co-processors, etc. But it is written
in a way that it can be used on top of any clock.

The implementation is pretty straight forward. The code creates
a thermal cooling device based on a pair of a struct device and a clock name.
The struct device is assumed to be usable by the OPP layer. The OPP layer
is used as source of the list of possible frequencies. The (cpufreq) frequency
table is then used as a map from frequencies to cooling states. Cooling
states are indexes to the frequency table.

The logic sits on top of common clock framework, specifically on clock
pre notifications. Any PRE_RATE_CHANGE is hijacked, and the transition is
only allowed when the new rate is within the thermal limit (cooling state -> freq).

When a thermal cooling device state transition is requested, the clock
is also checked to verify if the current clock rate is within the new
thermal limit.

Cc: Zhang Rui <>
Cc: Mike Turquette <>
Cc: Nishanth Menon <>
Cc: Pavel Machek <>
Cc: "Rafael J. Wysocki" <>
Cc: Len Brown <>
Cc: Greg Kroah-Hartman <>
Signed-off-by: default avatarEduardo Valentin <>
Signed-off-by: default avatarEduardo Valentin <>
parent fc14f9c1
......@@ -112,6 +112,18 @@ config CPU_THERMAL
If you want this support, you should say Y here.
bool "Generic clock cooling support"
depends on COMMON_CLK
depends on PM_OPP
This entry implements the generic clock cooling mechanism through
frequency clipping. Typically used to cool off co-processors. The
device that is configured to use this cooling mechanism will be
controlled to reduce clock frequency whenever temperature is high.
If you want this support, you should say Y here.
bool "Thermal emulation mode support"
......@@ -18,6 +18,9 @@ thermal_sys-$(CONFIG_THERMAL_GOV_USER_SPACE) += user_space.o
# cpufreq cooling
thermal_sys-$(CONFIG_CPU_THERMAL) += cpu_cooling.o
# clock cooling
thermal_sys-$(CONFIG_CLOCK_THERMAL) += clock_cooling.o
# platform thermal drivers
obj-$(CONFIG_SPEAR_THERMAL) += spear_thermal.o
obj-$(CONFIG_RCAR_THERMAL) += rcar_thermal.o
This diff is collapsed.
* linux/include/linux/clock_cooling.h
* Copyright (C) 2014 Eduardo Valentin <>
* Copyright (C) 2013 Texas Instruments Inc.
* Contact: Eduardo Valentin <>
* Highly based on cpu_cooling.c.
* Copyright (C) 2012 Samsung Electronics Co., Ltd(
* Copyright (C) 2012 Amit Daniel <>
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; version 2 of the License.
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* General Public License for more details.
#ifndef __CPU_COOLING_H__
#define __CPU_COOLING_H__
#include <linux/of.h>
#include <linux/thermal.h>
#include <linux/cpumask.h>
* clock_cooling_register - function to create clock cooling device.
* @dev: struct device pointer to the device used as clock cooling device.
* @clock_name: string containing the clock used as cooling mechanism.
struct thermal_cooling_device *
clock_cooling_register(struct device *dev, const char *clock_name);
* clock_cooling_unregister - function to remove clock cooling device.
* @cdev: thermal cooling device pointer.
void clock_cooling_unregister(struct thermal_cooling_device *cdev);
unsigned long clock_cooling_get_level(struct thermal_cooling_device *cdev,
unsigned long freq);
static inline struct thermal_cooling_device *
clock_cooling_register(struct device *dev, const char *clock_name)
return NULL;
static inline
void clock_cooling_unregister(struct thermal_cooling_device *cdev)
static inline
unsigned long clock_cooling_get_level(struct thermal_cooling_device *cdev,
unsigned long freq)
#endif /* __CPU_COOLING_H__ */
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