the generic thermal sysfs driver

The Generic Thermal sysfs driver for thermal management.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Thomas Sujith <sujith.thomas@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

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+Generic Thermal Sysfs driver How To
+=========================
+
+Written by Sujith Thomas <sujith.thomas@intel.com>, Zhang Rui <rui.zhang@intel.com>
+
+Updated: 2 January 2008
+
+Copyright (c)  2008 Intel Corporation
+
+
+0. Introduction
+
+The generic thermal sysfs provides a set of interfaces for thermal zone devices (sensors)
+and thermal cooling devices (fan, processor...) to register with the thermal management
+solution and to be a part of it.
+
+This how-to focusses on enabling new thermal zone and cooling devices to participate
+in thermal management.
+This solution is platform independent and any type of thermal zone devices and
+cooling devices should be able to make use of the infrastructure.
+
+The main task of the thermal sysfs driver is to expose thermal zone attributes as well
+as cooling device attributes to the user space.
+An intelligent thermal management application can make decisions based on inputs
+from thermal zone attributes (the current temperature and trip point temperature)
+and throttle appropriate devices.
+
+[0-*]   denotes any positive number starting from 0
+[1-*]   denotes any positive number starting from 1
+
+1. thermal sysfs driver interface functions
+
+1.1 thermal zone device interface
+1.1.1 struct thermal_zone_device *thermal_zone_device_register(char *name, int trips,
+                                void *devdata, struct thermal_zone_device_ops *ops)
+
+        This interface function adds a new thermal zone device (sensor) to
+        /sys/class/thermal folder as thermal_zone[0-*].
+        It tries to bind all the thermal cooling devices registered at the same time.
+
+        name: the thermal zone name.
+        trips: the total number of trip points this thermal zone supports.
+        devdata: device private data
+        ops: thermal zone device callbacks.
+                .bind: bind the thermal zone device with a thermal cooling device.
+                .unbind: unbing the thermal zone device with a thermal cooling device.
+                .get_temp: get the current temperature of the thermal zone.
+                .get_mode: get the current mode (user/kernel) of the thermal zone.
+                           "kernel" means thermal management is done in kernel.
+                           "user" will prevent kernel thermal driver actions upon trip points
+                           so that user applications can take charge of thermal management.
+                .set_mode: set the mode (user/kernel) of the thermal zone.
+                .get_trip_type: get the type of certain trip point.
+                .get_trip_temp: get the temperature above which the certain trip point
+                                will be fired.
+
+1.1.2 void thermal_zone_device_unregister(struct thermal_zone_device *tz)
+
+        This interface function removes the thermal zone device.
+        It deletes the corresponding entry form /sys/class/thermal folder and unbind all
+        the thermal cooling devices it uses.
+
+1.2 thermal cooling device interface
+1.2.1 struct thermal_cooling_device *thermal_cooling_device_register(char *name,
+                                        void *devdata, struct thermal_cooling_device_ops *)
+
+        This interface function adds a new thermal cooling device (fan/processor/...) to
+        /sys/class/thermal/ folder as cooling_device[0-*].
+        It tries to bind itself to all the thermal zone devices register at the same time.
+        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.
+
+1.2.2 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
+
+        This interface function remove the thermal cooling device.
+        It deletes the corresponding entry form /sys/class/thermal folder and unbind
+        itself from all the thermal zone devices using it.
+
+1.3 interface for binding a thermal zone device with a thermal cooling device
+1.3.1 int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz,
+                        int trip, struct thermal_cooling_device *cdev);
+
+        This interface function bind a thermal cooling device to the certain trip point
+        of a thermal zone device.
+        This function is usually called in the thermal zone device .bind callback.
+        tz: the thermal zone device
+        cdev: thermal cooling device
+        trip: indicates which trip point the cooling devices is associated with
+                 in this thermal zone.
+
+1.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
+                                int trip, struct thermal_cooling_device *cdev);
+
+        This interface function unbind a thermal cooling device from the certain trip point
+        of a thermal zone device.
+        This function is usually called in the thermal zone device .unbind callback.
+        tz: the thermal zone device
+        cdev: thermal cooling device
+        trip: indicates which trip point the cooling devices is associated with
+                in this thermal zone.
+
+2. sysfs attributes structure
+
+RO      read only value
+RW      read/write value
+
+All thermal sysfs attributes will be represented under /sys/class/thermal
+/sys/class/thermal/
+
+Thermal zone device sys I/F, created once it's registered:
+|thermal_zone[0-*]:
+        |-----type:                     Type of the thermal zone
+        |-----temp:                     Current temperature
+        |-----mode:                     Working mode of the thermal zone
+        |-----trip_point_[0-*]_temp:    Trip point temperature
+        |-----trip_point_[0-*]_type:    Trip point type
+
+Thermal cooling device sys I/F, created once it's registered:
+|cooling_device[0-*]:
+        |-----type :                    Type of the cooling device(processor/fan/...)
+        |-----max_state:                Maximum cooling state of the cooling device
+        |-----cur_state:                Current cooling state of the cooling device
+
+
+These two dynamic attributes are created/removed in pairs.
+They represent the relationship between a thermal zone and its associated cooling device.
+They are created/removed for each
+thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device successful exection.
+
+|thermal_zone[0-*]
+        |-----cdev[0-*]:                The [0-*]th cooling device in the current thermal zone
+        |-----cdev[0-*]_trip_point:     Trip point that cdev[0-*] is associated with
+
+
+***************************
+* Thermal zone attributes *
+***************************
+
+type                            Strings which represent the thermal zone type.
+                                This is given by thermal zone driver as part of registration.
+                                Eg: "ACPI thermal zone" indicates it's a ACPI thermal device
+                                RO
+                                Optional
+
+temp                            Current temperature as reported by thermal zone (sensor)
+                                Unit: degree celsius
+                                RO
+                                Required
+
+mode                            One of the predifned values in [kernel, user]
+                                This file gives information about the algorithm
+                                that is currently managing the thermal zone.
+                                It can be either default kernel based algorithm
+                                or user space application.
+                                RW
+                                Optional
+                                kernel  = Thermal management in kernel thermal zone driver.
+                                user    = Preventing kernel thermal zone driver actions upon
+                                          trip points so that user application can take full
+                                          charge of the thermal management.
+
+trip_point_[0-*]_temp           The temperature above which trip point will be fired
+                                Unit: degree celsius
+                                RO
+                                Optional
+
+trip_point_[0-*]_type           Strings which indicate the type of the trip point
+                                Eg. it can be one of critical, hot, passive,
+                                    active[0-*] for ACPI thermal zone.
+                                RO
+                                Optional
+
+cdev[0-*]                       Sysfs link to the thermal cooling device node where the sys I/F
+                                for cooling device throttling control represents.
+                                RO
+                                Optional
+
+cdev[0-*]_trip_point            The trip point with which cdev[0-*] is assocated in this thermal zone
+                                -1 means the cooling device is not associated with any trip point.
+                                RO
+                                Optional
+
+******************************
+* Cooling device  attributes *
+******************************
+
+type                            String which represents the type of device
+                                eg: For generic ACPI: this should be "Fan",
+                                "Processor" or "LCD"
+                                eg. For memory controller device on intel_menlow platform:
+                                this should be "Memory controller"
+                                RO
+                                Optional
+
+max_state                       The maximum permissible cooling state of this cooling device.
+                                RO
+                                Required
+
+cur_state                       The current cooling state of this cooling device.
+                                the value can any integer numbers between 0 and max_state,
+                                cur_state == 0 means no cooling
+                                cur_state == max_state means the maximum cooling.
+                                RW
+                                Required
+
+3. A simple implementation
+
+ACPI thermal zone may support multiple trip points like critical/hot/passive/active.
+If an ACPI thermal zone supports critical, passive, active[0] and active[1] at the same time,
+it may register itself as a thermale_zone_device (thermal_zone1) with 4 trip points in all.
+It has one processor and one fan, which are both registered as thermal_cooling_device.
+If the processor is listed in _PSL method, and the fan is listed in _AL0 method,
+the sys I/F structure will be built like this:
+
+/sys/class/thermal:
+
+|thermal_zone1:
+        |-----type:                     ACPI thermal zone
+        |-----temp:                     37
+        |-----mode:                     kernel
+        |-----trip_point_0_temp:        100
+        |-----trip_point_0_type:        critical
+        |-----trip_point_1_temp:        80
+        |-----trip_point_1_type:        passive
+        |-----trip_point_2_temp:        70
+        |-----trip_point_2_type:        active[0]
+        |-----trip_point_3_temp:        60
+        |-----trip_point_3_type:        active[1]
+        |-----cdev0:                    --->/sys/class/thermal/cooling_device0
+        |-----cdev0_trip_point:         1       /* cdev0 can be used for passive */
+        |-----cdev1:                    --->/sys/class/thermal/cooling_device3
+        |-----cdev1_trip_point:         2       /* cdev1 can be used for active[0]*/
+
+|cooling_device0:
+        |-----type:                     Processor
+        |-----max_state:                8
+        |-----cur_state:                0
+
+|cooling_device3:
+        |-----type:                     Fan
+        |-----max_state:                2
+        |-----cur_state:                0