[PATCH 6/9] Thermal: Add Documentation to new APIs
From: Durgadoss R
Date: Mon Jan 07 2013 - 02:18:21 EST
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@xxxxxxxxx>
Documentation/thermal/sysfs-api2.txt | 248 ++++++++++++++++++++++++++++++++++
1 file changed, 248 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
@@ -0,0 +1,248 @@
+Written by Durgadoss R <durgadoss.r@xxxxxxxxx>
+Copyright (c) 2012 Intel Corporation
+Created on: 4 November 2012
+Updated on: 18 December 2012
+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
+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.
+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
+ 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
+ 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
+ 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.
+ ts: Thermal sensor for which thresholds have to be enabled
+ num_thresholds: Number of thresholds supported by the sensor
+2.2: For Cooling Devices
+ 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
+ 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
+ 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
+ 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
+ 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
+ This function adds trip point information for the given sensor,
+ (under a given zone) under /sys/class/thermal/zoneX/thermal_trip/
+ 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.
+ 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
+ This function adds a 'map[0-*]' sysfs attribute under
+ /sys/class/thermal/zoneX/thermal_map/. Each map holds a space
+ separated list of values, that specify 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
+ |---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
+ |---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
+ |---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 all sensors
+ present in the thermal zone. All values are in mC.
+ |---hot: hot trip point value
+ |---critical: critical trip point value
+ |---passive: list of passive trip point values
+ |---active: list of active trip point values
+3.5: For Thermal Map
+ Each attribute represents the mapping/binding information between
+ a sensor and a cdev, together with a trip type.
+ |---mapX: mapping information
+ A typical map entry is like below:
+ trip_type sensor cdev trip_mask weight(s)
+ passive cpu proc 0x03 50 30
+ active cpu fan0 0x03 50 70
+ 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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