diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/devicetree/bindings/thermal/thermal.txt | 595 |
1 files changed, 595 insertions, 0 deletions
diff --git a/Documentation/devicetree/bindings/thermal/thermal.txt b/Documentation/devicetree/bindings/thermal/thermal.txt new file mode 100644 index 000000000000..f5db6b72a36f --- /dev/null +++ b/Documentation/devicetree/bindings/thermal/thermal.txt @@ -0,0 +1,595 @@ +* Thermal Framework Device Tree descriptor + +This file describes a generic binding to provide a way of +defining hardware thermal structure using device tree. +A thermal structure includes thermal zones and their components, +such as trip points, polling intervals, sensors and cooling devices +binding descriptors. + +The target of device tree thermal descriptors is to describe only +the hardware thermal aspects. The thermal device tree bindings are +not about how the system must control or which algorithm or policy +must be taken in place. + +There are five types of nodes involved to describe thermal bindings: +- thermal sensors: devices which may be used to take temperature + measurements. +- cooling devices: devices which may be used to dissipate heat. +- trip points: describe key temperatures at which cooling is recommended. The + set of points should be chosen based on hardware limits. +- cooling maps: used to describe links between trip points and cooling devices; +- thermal zones: used to describe thermal data within the hardware; + +The following is a description of each of these node types. + +* Thermal sensor devices + +Thermal sensor devices are nodes providing temperature sensing capabilities on +thermal zones. Typical devices are I2C ADC converters and bandgaps. These are +nodes providing temperature data to thermal zones. Thermal sensor devices may +control one or more internal sensors. + +Required property: +- #thermal-sensor-cells: Used to provide sensor device specific information + Type: unsigned while referring to it. Typically 0 on thermal sensor + Size: one cell nodes with only one sensor, and at least 1 on nodes + with several internal sensors, in order + to identify uniquely the sensor instances within + the IC. See thermal zone binding for more details + on how consumers refer to sensor devices. + +* Cooling device nodes + +Cooling devices are nodes providing control on power dissipation. There +are essentially two ways to provide control on power dissipation. First +is by means of regulating device performance, which is known as passive +cooling. A typical passive cooling is a CPU that has dynamic voltage and +frequency scaling (DVFS), and uses lower frequencies as cooling states. +Second is by means of activating devices in order to remove +the dissipated heat, which is known as active cooling, e.g. regulating +fan speeds. In both cases, cooling devices shall have a way to determine +the state of cooling in which the device is. + +Any cooling device has a range of cooling states (i.e. different levels +of heat dissipation). For example a fan's cooling states correspond to +the different fan speeds possible. Cooling states are referred to by +single unsigned integers, where larger numbers mean greater heat +dissipation. The precise set of cooling states associated with a device +(as referred to be the cooling-min-state and cooling-max-state +properties) should be defined in a particular device's binding. +For more examples of cooling devices, refer to the example sections below. + +Required properties: +- cooling-min-state: An integer indicating the smallest + Type: unsigned cooling state accepted. Typically 0. + Size: one cell + +- cooling-max-state: An integer indicating the largest + Type: unsigned cooling state accepted. + Size: one cell + +- #cooling-cells: Used to provide cooling device specific information + Type: unsigned while referring to it. Must be at least 2, in order + Size: one cell to specify minimum and maximum cooling state used + in the reference. The first cell is the minimum + cooling state requested and the second cell is + the maximum cooling state requested in the reference. + See Cooling device maps section below for more details + on how consumers refer to cooling devices. + +* Trip points + +The trip node is a node to describe a point in the temperature domain +in which the system takes an action. This node describes just the point, +not the action. + +Required properties: +- temperature: An integer indicating the trip temperature level, + Type: signed in millicelsius. + Size: one cell + +- hysteresis: A low hysteresis value on temperature property (above). + Type: unsigned This is a relative value, in millicelsius. + Size: one cell + +- type: a string containing the trip type. Expected values are: + "active": A trip point to enable active cooling + "passive": A trip point to enable passive cooling + "hot": A trip point to notify emergency + "critical": Hardware not reliable. + Type: string + +* Cooling device maps + +The cooling device maps node is a node to describe how cooling devices +get assigned to trip points of the zone. The cooling devices are expected +to be loaded in the target system. + +Required properties: +- cooling-device: A phandle of a cooling device with its specifier, + Type: phandle + referring to which cooling device is used in this + cooling specifier binding. In the cooling specifier, the first cell + is the minimum cooling state and the second cell + is the maximum cooling state used in this map. +- trip: A phandle of a trip point node within the same thermal + Type: phandle of zone. + trip point node + +Optional property: +- contribution: The cooling contribution to the thermal zone of the + Type: unsigned referred cooling device at the referred trip point. + Size: one cell The contribution is a ratio of the sum + of all cooling contributions within a thermal zone. + +Note: Using the THERMAL_NO_LIMIT (-1UL) constant in the cooling-device phandle +limit specifier means: +(i) - minimum state allowed for minimum cooling state used in the reference. +(ii) - maximum state allowed for maximum cooling state used in the reference. +Refer to include/dt-bindings/thermal/thermal.h for definition of this constant. + +* Thermal zone nodes + +The thermal zone node is the node containing all the required info +for describing a thermal zone, including its cooling device bindings. The +thermal zone node must contain, apart from its own properties, one sub-node +containing trip nodes and one sub-node containing all the zone cooling maps. + +Required properties: +- polling-delay: The maximum number of milliseconds to wait between polls + Type: unsigned when checking this thermal zone. + Size: one cell + +- polling-delay-passive: The maximum number of milliseconds to wait + Type: unsigned between polls when performing passive cooling. + Size: one cell + +- thermal-sensors: A list of thermal sensor phandles and sensor specifier + Type: list of used while monitoring the thermal zone. + phandles + sensor + specifier + +- trips: A sub-node which is a container of only trip point nodes + Type: sub-node required to describe the thermal zone. + +- cooling-maps: A sub-node which is a container of only cooling device + Type: sub-node map nodes, used to describe the relation between trips + and cooling devices. + +Optional property: +- coefficients: An array of integers (one signed cell) containing + Type: array coefficients to compose a linear relation between + Elem size: one cell the sensors listed in the thermal-sensors property. + Elem type: signed Coefficients defaults to 1, in case this property + is not specified. A simple linear polynomial is used: + Z = c0 * x0 + c1 + x1 + ... + c(n-1) * x(n-1) + cn. + + The coefficients are ordered and they match with sensors + by means of sensor ID. Additional coefficients are + interpreted as constant offset. + +Note: The delay properties are bound to the maximum dT/dt (temperature +derivative over time) in two situations for a thermal zone: +(i) - when passive cooling is activated (polling-delay-passive); and +(ii) - when the zone just needs to be monitored (polling-delay) or +when active cooling is activated. + +The maximum dT/dt is highly bound to hardware power consumption and dissipation +capability. The delays should be chosen to account for said max dT/dt, +such that a device does not cross several trip boundaries unexpectedly +between polls. Choosing the right polling delays shall avoid having the +device in temperature ranges that may damage the silicon structures and +reduce silicon lifetime. + +* The thermal-zones node + +The "thermal-zones" node is a container for all thermal zone nodes. It shall +contain only sub-nodes describing thermal zones as in the section +"Thermal zone nodes". The "thermal-zones" node appears under "/". + +* Examples + +Below are several examples on how to use thermal data descriptors +using device tree bindings: + +(a) - CPU thermal zone + +The CPU thermal zone example below describes how to setup one thermal zone +using one single sensor as temperature source and many cooling devices and +power dissipation control sources. + +#include <dt-bindings/thermal/thermal.h> + +cpus { + /* + * Here is an example of describing a cooling device for a DVFS + * capable CPU. The CPU node describes its four OPPs. + * The cooling states possible are 0..3, and they are + * used as OPP indexes. The minimum cooling state is 0, which means + * all four OPPs can be available to the system. The maximum + * cooling state is 3, which means only the lowest OPPs (198MHz@0.85V) + * can be available in the system. + */ + cpu0: cpu@0 { + ... + operating-points = < + /* kHz uV */ + 970000 1200000 + 792000 1100000 + 396000 950000 + 198000 850000 + >; + cooling-min-state = <0>; + cooling-max-state = <3>; + #cooling-cells = <2>; /* min followed by max */ + }; + ... +}; + +&i2c1 { + ... + /* + * A simple fan controller which supports 10 speeds of operation + * (represented as 0-9). + */ + fan0: fan@0x48 { + ... + cooling-min-state = <0>; + cooling-max-state = <9>; + #cooling-cells = <2>; /* min followed by max */ + }; +}; + +ocp { + ... + /* + * A simple IC with a single bandgap temperature sensor. + */ + bandgap0: bandgap@0x0000ED00 { + ... + #thermal-sensor-cells = <0>; + }; +}; + +thermal-zones { + cpu-thermal: cpu-thermal { + polling-delay-passive = <250>; /* milliseconds */ + polling-delay = <1000>; /* milliseconds */ + + thermal-sensors = <&bandgap0>; + + trips { + cpu-alert0: cpu-alert { + temperature = <90000>; /* millicelsius */ + hysteresis = <2000>; /* millicelsius */ + type = "active"; + }; + cpu-alert1: cpu-alert { + temperature = <100000>; /* millicelsius */ + hysteresis = <2000>; /* millicelsius */ + type = "passive"; + }; + cpu-crit: cpu-crit { + temperature = <125000>; /* millicelsius */ + hysteresis = <2000>; /* millicelsius */ + type = "critical"; + }; + }; + + cooling-maps { + map0 { + trip = <&cpu-alert0>; + cooling-device = <&fan0 THERMAL_NO_LIMITS 4>; + }; + map1 { + trip = <&cpu-alert1>; + cooling-device = <&fan0 5 THERMAL_NO_LIMITS>; + }; + map2 { + trip = <&cpu-alert1>; + cooling-device = + <&cpu0 THERMAL_NO_LIMITS THERMAL_NO_LIMITS>; + }; + }; + }; +}; + +In the example above, the ADC sensor (bandgap0) at address 0x0000ED00 is +used to monitor the zone 'cpu-thermal' using its sole sensor. A fan +device (fan0) is controlled via I2C bus 1, at address 0x48, and has ten +different cooling states 0-9. It is used to remove the heat out of +the thermal zone 'cpu-thermal' using its cooling states +from its minimum to 4, when it reaches trip point 'cpu-alert0' +at 90C, as an example of active cooling. The same cooling device is used at +'cpu-alert1', but from 5 to its maximum state. The cpu@0 device is also +linked to the same thermal zone, 'cpu-thermal', as a passive cooling device, +using all its cooling states at trip point 'cpu-alert1', +which is a trip point at 100C. On the thermal zone 'cpu-thermal', at the +temperature of 125C, represented by the trip point 'cpu-crit', the silicon +is not reliable anymore. + +(b) - IC with several internal sensors + +The example below describes how to deploy several thermal zones based off a +single sensor IC, assuming it has several internal sensors. This is a common +case on SoC designs with several internal IPs that may need different thermal +requirements, and thus may have their own sensor to monitor or detect internal +hotspots in their silicon. + +#include <dt-bindings/thermal/thermal.h> + +ocp { + ... + /* + * A simple IC with several bandgap temperature sensors. + */ + bandgap0: bandgap@0x0000ED00 { + ... + #thermal-sensor-cells = <1>; + }; +}; + +thermal-zones { + cpu-thermal: cpu-thermal { + polling-delay-passive = <250>; /* milliseconds */ + polling-delay = <1000>; /* milliseconds */ + + /* sensor ID */ + thermal-sensors = <&bandgap0 0>; + + trips { + /* each zone within the SoC may have its own trips */ + cpu-alert: cpu-alert { + temperature = <100000>; /* millicelsius */ + hysteresis = <2000>; /* millicelsius */ + type = "passive"; + }; + cpu-crit: cpu-crit { + temperature = <125000>; /* millicelsius */ + hysteresis = <2000>; /* millicelsius */ + type = "critical"; + }; + }; + + cooling-maps { + /* each zone within the SoC may have its own cooling */ + ... + }; + }; + + gpu-thermal: gpu-thermal { + polling-delay-passive = <120>; /* milliseconds */ + polling-delay = <1000>; /* milliseconds */ + + /* sensor ID */ + thermal-sensors = <&bandgap0 1>; + + trips { + /* each zone within the SoC may have its own trips */ + gpu-alert: gpu-alert { + temperature = <90000>; /* millicelsius */ + hysteresis = <2000>; /* millicelsius */ + type = "passive"; + }; + gpu-crit: gpu-crit { + temperature = <105000>; /* millicelsius */ + hysteresis = <2000>; /* millicelsius */ + type = "critical"; + }; + }; + + cooling-maps { + /* each zone within the SoC may have its own cooling */ + ... + }; + }; + + dsp-thermal: dsp-thermal { + polling-delay-passive = <50>; /* milliseconds */ + polling-delay = <1000>; /* milliseconds */ + + /* sensor ID */ + thermal-sensors = <&bandgap0 2>; + + trips { + /* each zone within the SoC may have its own trips */ + dsp-alert: gpu-alert { + temperature = <90000>; /* millicelsius */ + hysteresis = <2000>; /* millicelsius */ + type = "passive"; + }; + dsp-crit: gpu-crit { + temperature = <135000>; /* millicelsius */ + hysteresis = <2000>; /* millicelsius */ + type = "critical"; + }; + }; + + cooling-maps { + /* each zone within the SoC may have its own cooling */ + ... + }; + }; +}; + +In the example above, there is one bandgap IC which has the capability to +monitor three sensors. The hardware has been designed so that sensors are +placed on different places in the DIE to monitor different temperature +hotspots: one for CPU thermal zone, one for GPU thermal zone and the +other to monitor a DSP thermal zone. + +Thus, there is a need to assign each sensor provided by the bandgap IC +to different thermal zones. This is achieved by means of using the +#thermal-sensor-cells property and using the first cell of the sensor +specifier as sensor ID. In the example, then, <bandgap 0> is used to +monitor CPU thermal zone, <bandgap 1> is used to monitor GPU thermal +zone and <bandgap 2> is used to monitor DSP thermal zone. Each zone +may be uncorrelated, having its own dT/dt requirements, trips +and cooling maps. + + +(c) - Several sensors within one single thermal zone + +The example below illustrates how to use more than one sensor within +one thermal zone. + +#include <dt-bindings/thermal/thermal.h> + +&i2c1 { + ... + /* + * A simple IC with a single temperature sensor. + */ + adc: sensor@0x49 { + ... + #thermal-sensor-cells = <0>; + }; +}; + +ocp { + ... + /* + * A simple IC with a single bandgap temperature sensor. + */ + bandgap0: bandgap@0x0000ED00 { + ... + #thermal-sensor-cells = <0>; + }; +}; + +thermal-zones { + cpu-thermal: cpu-thermal { + polling-delay-passive = <250>; /* milliseconds */ + polling-delay = <1000>; /* milliseconds */ + + thermal-sensors = <&bandgap0>, /* cpu */ + <&adc>; /* pcb north */ + + /* hotspot = 100 * bandgap - 120 * adc + 484 */ + coefficients = <100 -120 484>; + + trips { + ... + }; + + cooling-maps { + ... + }; + }; +}; + +In some cases, there is a need to use more than one sensor to extrapolate +a thermal hotspot in the silicon. The above example illustrates this situation. +For instance, it may be the case that a sensor external to CPU IP may be placed +close to CPU hotspot and together with internal CPU sensor, it is used +to determine the hotspot. Assuming this is the case for the above example, +the hypothetical extrapolation rule would be: + hotspot = 100 * bandgap - 120 * adc + 484 + +In other context, the same idea can be used to add fixed offset. For instance, +consider the hotspot extrapolation rule below: + hotspot = 1 * adc + 6000 + +In the above equation, the hotspot is always 6C higher than what is read +from the ADC sensor. The binding would be then: + thermal-sensors = <&adc>; + + /* hotspot = 1 * adc + 6000 */ + coefficients = <1 6000>; + +(d) - Board thermal + +The board thermal example below illustrates how to setup one thermal zone +with many sensors and many cooling devices. + +#include <dt-bindings/thermal/thermal.h> + +&i2c1 { + ... + /* + * An IC with several temperature sensor. + */ + adc-dummy: sensor@0x50 { + ... + #thermal-sensor-cells = <1>; /* sensor internal ID */ + }; +}; + +thermal-zones { + batt-thermal { + polling-delay-passive = <500>; /* milliseconds */ + polling-delay = <2500>; /* milliseconds */ + + /* sensor ID */ + thermal-sensors = <&adc-dummy 4>; + + trips { + ... + }; + + cooling-maps { + ... + }; + }; + + board-thermal: board-thermal { + polling-delay-passive = <1000>; /* milliseconds */ + polling-delay = <2500>; /* milliseconds */ + + /* sensor ID */ + thermal-sensors = <&adc-dummy 0>, /* pcb top edge */ + <&adc-dummy 1>, /* lcd */ + <&adc-dymmy 2>; /* back cover */ + /* + * An array of coefficients describing the sensor + * linear relation. E.g.: + * z = c1*x1 + c2*x2 + c3*x3 + */ + coefficients = <1200 -345 890>; + + trips { + /* Trips are based on resulting linear equation */ + cpu-trip: cpu-trip { + temperature = <60000>; /* millicelsius */ + hysteresis = <2000>; /* millicelsius */ + type = "passive"; + }; + gpu-trip: gpu-trip { + temperature = <55000>; /* millicelsius */ + hysteresis = <2000>; /* millicelsius */ + type = "passive"; + } + lcd-trip: lcp-trip { + temperature = <53000>; /* millicelsius */ + hysteresis = <2000>; /* millicelsius */ + type = "passive"; + }; + crit-trip: crit-trip { + temperature = <68000>; /* millicelsius */ + hysteresis = <2000>; /* millicelsius */ + type = "critical"; + }; + }; + + cooling-maps { + map0 { + trip = <&cpu-trip>; + cooling-device = <&cpu0 0 2>; + contribution = <55>; + }; + map1 { + trip = <&gpu-trip>; + cooling-device = <&gpu0 0 2>; + contribution = <20>; + }; + map2 { + trip = <&lcd-trip>; + cooling-device = <&lcd0 5 10>; + contribution = <15>; + }; + }; + }; +}; + +The above example is a mix of previous examples, a sensor IP with several internal +sensors used to monitor different zones, one of them is composed by several sensors and +with different cooling devices. |