Message-ID: <1360315272.2242.53.camel@rzhang1-mobl4>
Date:	Fri, 08 Feb 2013 17:21:12 +0800
From:	Zhang Rui <rui.zhang@...el.com>
To:	Durgadoss R <durgadoss.r@...el.com>
Cc:	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	eduardo.valentin@...com, hongbo.zhang@...aro.org, wni@...dia.com
Subject: Re: [PATCH 6/8] Thermal: Add Documentation to new APIs

On Tue, 2013-02-05 at 16:16 +0530, Durgadoss R wrote:
> This patch adds Documentation for the new APIs
> introduced in this patch set. The documentation
> also has a model sysfs structure for reference.
> 
> Signed-off-by: Durgadoss R <durgadoss.r@...el.com>
> ---
>  Documentation/thermal/sysfs-api2.txt |  247 ++++++++++++++++++++++++++++++++++
>  1 file changed, 247 insertions(+)
>  create mode 100644 Documentation/thermal/sysfs-api2.txt
> 
> diff --git a/Documentation/thermal/sysfs-api2.txt b/Documentation/thermal/sysfs-api2.txt
> new file mode 100644
> index 0000000..24e23f4
> --- /dev/null
> +++ b/Documentation/thermal/sysfs-api2.txt
> @@ -0,0 +1,247 @@
> +Thermal Framework
> +-----------------
> +
> +Written by Durgadoss R <durgadoss.r@...el.com>
> +Copyright (c) 2012 Intel Corporation
> +
> +Created on: 4 November 2012
> +Updated on: 5 February 2013
> +
> +0. Introduction
> +---------------
> +The Linux thermal framework provides a set of interfaces for thermal
> +sensors and thermal cooling devices (fan, processor...) to register
> +with the thermal management solution and to be a part of it.
> +
> +This document focuses on how to enable new thermal sensors and cooling
> +devices to participate in thermal management. This solution is intended
> +to be 'light-weight' and platform/architecture independent. Any thermal
> +sensor/cooling device should be able to use the infrastructure easily.
> +
> +The goal of thermal framework is to expose the thermal sensor/zone and
> +cooling device attributes in a consistent way. This will help the
> +thermal governors to make use of the information to manage platform
> +thermals efficiently.
> +
> +The thermal sensor source file can be generic (can be any sensor driver,
> +in any subsystem). This driver will use the sensor APIs and register with
> +thermal framework to participate in platform Thermal management. This
> +does not (and should not) know about which zone it belongs to, or any
> +other information about platform thermals. A sensor driver is a standalone
> +piece of code, which can optionally register with thermal framework.
> +
> +However, for any platform, there should be a platformX_thermal.c file,
> +which will know about the platform thermal characteristics (like how many
> +sensors, zones, cooling devices, etc.. And how they are related to each other
> +i.e the mapping information). Only in this file, the zone level APIs should
> +be used, in which case the file will have all information required to attach
> +various sensors to a particular zone.
> +
> +This way, we can have one platform level thermal file, which can support
> +multiple platforms (may be)using the same set of sensors (but)binded in
> +a different way. This file can get the platform thermal information
> +through Firmware, ACPI tables, device tree etc.
> +
> +Unfortunately, today we don't have many drivers that can be clearly
> +differentiated as 'sensor_file.c' and 'platform_thermal_file.c'.
> +But very soon we will need/have. The reason I am saying this is because
> +we are seeing a lot of chip drivers, starting to use thermal framework,
> +and we should keep it really light-weight for them to do so.
> +
> +An Example: drivers/hwmon/emc1403.c - a generic thermal chip driver
> +In one platform this sensor can belong to 'ZoneA' and in another the
> +same can belong to 'ZoneB'. But, emc1403.c does not really care about
> +where does it belong. It just reports temperature.
> +
> +1. Terminology
> +--------------
> +This section describes the terminology used in the rest of this
> +document as well as the thermal framework code.
> +
> +thermal_sensor: Hardware that can report temperature of a particular
> +		spot in the platform, where it is placed. The temperature
> +		reported by the sensor is the 'real' temperature reported
> +		by the hardware.
> +thermal_zone:	A virtual area on the device, that gets heated up. It may
> +		have one or more thermal sensors attached to it.
> +cooling_device:	Any component that can help in reducing the temperature of
> +		a 'hot spot' either by reducing its performance (passive
> +		cooling) or by other means(Active cooling E.g. Fan)
> +
> +trip_points:	Various temperature levels for each sensor. As of now, we
> +		have four levels namely active, passive, hot and critical.
> +		Hot and critical trip point support only one value whereas
> +		active and passive can have any number of values. These
> +		temperature values can come from platform data, and are
> +		exposed through sysfs in a consistent manner. Stand-alone
> +		thermal sensor drivers are not expected to know these values.
> +		These values are RO.
> +thresholds:	These are programmable temperature limits, on reaching which
> +		the thermal sensor generates an interrupt. The framework is
> +		notified about this interrupt to take appropriate action.
> +		There can be as many number of thresholds as that of the
> +		hardware supports. These values are RW.
> +
> +thermal_map:	This provides the mapping (aka binding) information between
> +		various sensors and cooling devices in a particular zone.
> +		Typically, this also comes from platform data; Stand-alone
> +		sensor drivers or cooling device drivers are not expected
> +		to know these mapping information.
> +
> +2. Thermal framework APIs
> +-------------------------
> +2.1: For Thermal Sensors
> +2.1.1 thermal_sensor_register:
> +	This function creates a new sensor directory under /sys/class/thermal/
> +	as sensor[0-*]. This API is expected to be called by thermal sensor
> +	drivers. These drivers may or may not be in thermal subsystem. This
> +	function returns a thermal_sensor structure on success and appropriate
> +	error on failure.
> +
> +	name: Name of the sensor
> +	count: Number of programmable thresholds associated with this sensor
> +	devdata: Device private data
> +	ops: Thermal sensor callbacks
> +		.get_temp: obtain the current temperature of the sensor
> +		.get_trend: obtain the trend of the sensor
> +		.get_threshold: get a particular threshold temperature
> +		.set_threshold: set a particular threshold temperature
> +		.get_hyst: get hysteresis value associated with a threshold
> +		.set_hyst: set hysteresis value associated with a threshold
> +
> +2.1.2 thermal_sensor_unregister:
> +	This function deletes the sensor directory under /sys/class/thermal/
> +	for the given sensor. Thermal sensor drivers may call this API
> +	during the driver's 'exit' routine.
> +
> +	ts: Thermal sensor that has to be unregistered
> +
> +2.1.3 enable_sensor_thresholds:
> +	This function creates 'threshold[0-*]' attributes under a particular
> +	sensorX directory. These values are RW. This function is called by
> +	the sensr driver only if the sensor supports interrupt mechanism.

s/sensr/sensor

> +
> +	ts: Thermal sensor for which thresholds have to be enabled
> +	num_thresholds: Number of thresholds supported by the sensor
> +
> +2.2: For Cooling Devices
> +2.2.1 thermal_cooling_device_register:
> +	This function adds a new thermal cooling device (fan/processor/...)
> +	to /sys/class/thermal/ folder as cooling_device[0-*]. This function
> +	is expected to be called by cooling device drivers that may be
> +	present in other subsystems also.
> +
> +	name: the cooling device name
> +	devdata: device private data
> +	ops: thermal cooling devices callbacks
> +	.get_max_state: get the Maximum throttle state of the cooling device
> +	.get_cur_state: get the Current throttle state of the cooling device
> +	.set_cur_state: set the Current throttle state of the cooling device
> +
> +2.2.2 thermal_cooling_device_unregister:
> +	This function deletes the given cdev entry form /sys/class/thermal;
> +	and also cleans all the symlinks referred from various zones.
> +
> +	cdev: Cooling device to be unregistered
> +
> +2.3: For Thermal Zones
> +2.3.1 create_thermal_zone:
> +	This function adds a new 'zone' under /sys/class/thermal/
> +	directory as zone[0-*]. This zone has at least one thermal
> +	sensor and at most MAX_SENSORS_PER_ZONE number of sensors
> +	attached to it. Similarly, this zone has at least one cdev
> +	and at most MAX_CDEVS_PER_ZONE number of cdevs attached to it.
> +	Both the MAX_*_PER_ZONE values are configurable, through
> +	Kconfig option(during 'menuconfig').
> +
> +	name: Name of the thermal zone
> +	devdata: Device private data
> +
> +2.3.2 add_sensor_to_zone
> +	This function adds a 'sensorX' entry under /sys/class/thermal/
> +	zoneY/ directory. This 'sensorX' is a symlink to the actual
> +	sensor entry under /sys/class/thermal/. Correspondingly, the
> +	method remove_sensor_from_zone deletes the symlink.
> +
> +	tz: thermal zone structure
> +	ts: thermal sensor structure
> +
> +2.3.3 add_cdev_to_zone
> +	This function adds a 'cdevX' entry under /sys/class/thermal/
> +	zoneY/ directory. This 'cdevX' is a symlink to the actual
> +	cdev entry under /sys/class/thermal/. Correspondingly, the
> +	method remove_cdev_from_zone deletes the symlink.
> +
> +	tz: thermal zone structure
> +	cdev: thermal cooling device structure
> +
> +2.4 For Thermal Trip
> +2.4.1 add_sensor_trip_info
> +	This function adds trip point information for the given sensor,
> +	(under a given zone) under /sys/class/thermal/zoneX/.
> +	This API creates 4 sysfs attributes namely active, passive, hot,
> +	and critical. Each of these hold one or more trip point temperature
> +	values, as provided from platform data.
if this is true, actually it is, it breaks the sysfs "one value per
file" rule.
we should have multiple active/passive attributes if there are multiple
trip points.

thanks,
rui
> +
> +	tz: thermal zone structure
> +	ts: thermal sensor to which the trip points are attached
> +	trip: trip point structure. Usually obtained from platform data
> +
> +2.5 For Thermal Map
> +2.5.1 add_map_entry
> +	This function adds a 'map[0-*]' sysfs attribute under
> +	/sys/class/thermal/zoneX/mapY_*. Each map attribute helps
> +	to describe the binding relationship between a sensor and
> +	a cdev in the given zone. The map structure is typically
> +	obtained as platform data. For example, through ACPI tables,
> +	SFI tables, Device tree etc.
> +
> +	tz: thermal zone to which a 'map' is being added
> +	map: thermal_map structure
> +
> +3. Sysfs attributes structure
> +-----------------------------
> +Thermal sysfs attributes will be represented under /sys/class/thermal.
> +
> +3.1: For Thermal Sensors
> +	/sys/class/thermal/sensor[0-*]:
> +		|---type:		Name of the thermal sensor
> +		|---temp_input:		Current temperature in mC
> +		|---threshold[0-*]:	Threshold temperature in mC
> +		|---threshold[0-*]_hyst:Optional hysteresis value in mC
> +
> +3.2: For Thermal Cooling Devices
> +	/sys/class/thermal/cooling_device[0-*]:
> +		|---type:		Type of the cooling device
> +		|---max_state:		Maximum throttle state of the cdev
> +		|---cur_state:		Current throttle state of the cdev
> +
> +3.3: For Thermal Zones
> +	/sys/class/thermal/zone[0-*]:
> +		|---name:		Name of the thermal
> +		|---sensorX:		Symlink to ../sensorX
> +		|---cdevY:		Symlink to ../cdevY
> +		|---thermal_trip:	trip point values for sensors
> +		|---thermal_map:	mapping info between sensors and cdevs
> +
> +3.4: For Thermal Trip
> +	This attribute represents the trip point values for a sensor(Y)
> +	present in the thermal zone(X). All values are in mC.
> +	/sys/class/thermal/zoneX/:
> +		|---sensorY_trip_hot:		hot trip point
> +		|---sensorY_trip_critical:	critical trip point
> +		|---sensorY_trip_passive:	passive trip point
> +		|---sensorY_trip_active:	active trip point
> +
> +3.5: For Thermal Map
> +	Each attribute represents the mapping/binding information between
> +	a sensor and a cdev, together with a trip type.
> +	/sys/class/thermal/zoneX/:
> +		|---mapY_trip_type:		active/passive
> +		|---mapY_sensor_name:		cpu
> +		|---mapY_cdev_name:		proc
> +		|---mapY_trip_mask:		0x03
> +		|---mapY_weights:		50 30
> +
> +	The trip mask is a bit string; if 'n' th bit is set, then for
> +	trip point 'n' this cdev is throttled with the given weight[n].


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