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SubjectRe: [PATCH 6/8] Thermal: Add Documentation to new APIs
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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@intel.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@intel.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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