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linux-next/Documentation/thermal/cpu-cooling-api.txt

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thermal: add generic cpufreq cooling implementation This patchset introduces a new generic cooling device based on cpufreq that can be used on non-ACPI platforms. As a proof of concept, we have drivers for the following platforms using this mechanism now: * Samsung Exynos (Exynos4 and Exynos5) in the current patchset. * Freescale i.MX (git://git.linaro.org/people/amitdanielk/linux.git imx6q_thermal) There is a small change in cpufreq cooling registration APIs, so a minor change is needed for Freescale platforms. Brief Description: 1) The generic cooling devices code is placed inside driver/thermal/* as placing inside acpi folder will need un-necessary enabling of acpi code. This code is architecture independent. 2) This patchset adds generic cpu cooling low level implementation through frequency clipping. In future, other cpu related cooling devices may be added here. An ACPI version of this already exists (drivers/acpi/processor_thermal.c) .But this will be useful for platforms like ARM using the generic thermal interface along with the generic cpu cooling devices. The cooling device registration API's return cooling device pointers which can be easily binded with the thermal zone trip points. The important APIs exposed are, a) struct thermal_cooling_device *cpufreq_cooling_register( struct cpumask *clip_cpus) b) void cpufreq_cooling_unregister(struct thermal_cooling_device *cdev) 3) Samsung exynos platform thermal implementation is done using the generic cpu cooling APIs and the new trip type. The temperature sensor driver present in the hwmon folder(registered as hwmon driver) is moved to thermal folder and registered as a thermal driver. A simple data/control flow diagrams is shown below, Core Linux thermal <-----> Exynos thermal interface <----- Temperature Sensor | | \|/ | Cpufreq cooling device <--------------- TODO: *Will send the DT enablement patches later after the driver is merged. This patch: Add support for generic cpu thermal cooling low level implementations using frequency scaling up/down based on the registration parameters. Different cpu related cooling devices can be registered by the user and the binding of these cooling devices to the corresponding trip points can be easily done as the registration APIs return the cooling device pointer. The user of these APIs are responsible for passing clipping frequency . The drivers can also register to recieve notification about any cooling action called. [akpm@linux-foundation.org: fix comment layout] Signed-off-by: Amit Daniel Kachhap <amit.kachhap@linaro.org> Cc: Guenter Roeck <guenter.roeck@ericsson.com> Cc: SangWook Ju <sw.ju@samsung.com> Cc: Durgadoss <durgadoss.r@intel.com> Cc: Len Brown <lenb@kernel.org> Cc: Jean Delvare <khali@linux-fr.org> Cc: Kyungmin Park <kmpark@infradead.org> Cc: Kukjin Kim <kgene.kim@samsung.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Amit Daniel Kachhap <amit.daniel@samsung.com> Signed-off-by: Zhang Rui <rui.zhang@intel.com>
2012-08-16 19:41:40 +08:00
CPU cooling APIs How To
===================================
Written by Amit Daniel Kachhap <amit.kachhap@linaro.org>
Updated: 12 May 2012
Copyright (c) 2012 Samsung Electronics Co., Ltd(http://www.samsung.com)
0. Introduction
The generic cpu cooling(freq clipping) provides registration/unregistration APIs
to the caller. The binding of the cooling devices to the trip point is left for
the user. The registration APIs returns the cooling device pointer.
1. cpu cooling APIs
1.1 cpufreq registration/unregistration APIs
1.1.1 struct thermal_cooling_device *cpufreq_cooling_register(
struct cpumask *clip_cpus)
This interface function registers the cpufreq cooling device with the name
"thermal-cpufreq-%x". This api can support multiple instances of cpufreq
cooling devices.
clip_cpus: cpumask of cpus where the frequency constraints will happen.
1.1.2 void cpufreq_cooling_unregister(struct thermal_cooling_device *cdev)
This interface function unregisters the "thermal-cpufreq-%x" cooling device.
cdev: Cooling device pointer which has to be unregistered.
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