1 * Thermal Framework Device Tree descriptor
3 This file describes a generic binding to provide a way of
4 defining hardware thermal structure using device tree.
5 A thermal structure includes thermal zones and their components,
6 such as trip points, polling intervals, sensors and cooling devices
9 The target of device tree thermal descriptors is to describe only
10 the hardware thermal aspects. The thermal device tree bindings are
11 not about how the system must control or which algorithm or policy
12 must be taken in place.
14 There are five types of nodes involved to describe thermal bindings:
15 - thermal sensors: devices which may be used to take temperature
17 - cooling devices: devices which may be used to dissipate heat.
18 - trip points: describe key temperatures at which cooling is recommended. The
19 set of points should be chosen based on hardware limits.
20 - cooling maps: used to describe links between trip points and cooling devices;
21 - thermal zones: used to describe thermal data within the hardware;
23 The following is a description of each of these node types.
25 * Thermal sensor devices
27 Thermal sensor devices are nodes providing temperature sensing capabilities on
28 thermal zones. Typical devices are I2C ADC converters and bandgaps. These are
29 nodes providing temperature data to thermal zones. Thermal sensor devices may
30 control one or more internal sensors.
33 - #thermal-sensor-cells: Used to provide sensor device specific information
34 Type: unsigned while referring to it. Typically 0 on thermal sensor
35 Size: one cell nodes with only one sensor, and at least 1 on nodes
36 with several internal sensors, in order
37 to identify uniquely the sensor instances within
38 the IC. See thermal zone binding for more details
39 on how consumers refer to sensor devices.
41 * Cooling device nodes
43 Cooling devices are nodes providing control on power dissipation. There
44 are essentially two ways to provide control on power dissipation. First
45 is by means of regulating device performance, which is known as passive
46 cooling. A typical passive cooling is a CPU that has dynamic voltage and
47 frequency scaling (DVFS), and uses lower frequencies as cooling states.
48 Second is by means of activating devices in order to remove
49 the dissipated heat, which is known as active cooling, e.g. regulating
50 fan speeds. In both cases, cooling devices shall have a way to determine
51 the state of cooling in which the device is.
53 Any cooling device has a range of cooling states (i.e. different levels
54 of heat dissipation). For example a fan's cooling states correspond to
55 the different fan speeds possible. Cooling states are referred to by
56 single unsigned integers, where larger numbers mean greater heat
57 dissipation. The precise set of cooling states associated with a device
58 should be defined in a particular device's binding.
59 For more examples of cooling devices, refer to the example sections below.
62 - #cooling-cells: Used to provide cooling device specific information
63 Type: unsigned while referring to it. Must be at least 2, in order
64 Size: one cell to specify minimum and maximum cooling state used
65 in the reference. The first cell is the minimum
66 cooling state requested and the second cell is
67 the maximum cooling state requested in the reference.
68 See Cooling device maps section below for more details
69 on how consumers refer to cooling devices.
73 The trip node is a node to describe a point in the temperature domain
74 in which the system takes an action. This node describes just the point,
78 - temperature: An integer indicating the trip temperature level,
79 Type: signed in millicelsius.
82 - hysteresis: A low hysteresis value on temperature property (above).
83 Type: unsigned This is a relative value, in millicelsius.
86 - type: a string containing the trip type. Expected values are:
87 "active": A trip point to enable active cooling
88 "passive": A trip point to enable passive cooling
89 "hot": A trip point to notify emergency
90 "critical": Hardware not reliable.
95 The cooling device maps node is a node to describe how cooling devices
96 get assigned to trip points of the zone. The cooling devices are expected
97 to be loaded in the target system.
100 - cooling-device: A phandle of a cooling device with its specifier,
101 Type: phandle + referring to which cooling device is used in this
102 cooling specifier binding. In the cooling specifier, the first cell
103 is the minimum cooling state and the second cell
104 is the maximum cooling state used in this map.
105 - trip: A phandle of a trip point node within the same thermal
106 Type: phandle of zone.
110 - contribution: The cooling contribution to the thermal zone of the
111 Type: unsigned referred cooling device at the referred trip point.
112 Size: one cell The contribution is a ratio of the sum
113 of all cooling contributions within a thermal zone.
115 Note: Using the THERMAL_NO_LIMIT (-1UL) constant in the cooling-device phandle
116 limit specifier means:
117 (i) - minimum state allowed for minimum cooling state used in the reference.
118 (ii) - maximum state allowed for maximum cooling state used in the reference.
119 Refer to include/dt-bindings/thermal/thermal.h for definition of this constant.
123 The thermal zone node is the node containing all the required info
124 for describing a thermal zone, including its cooling device bindings. The
125 thermal zone node must contain, apart from its own properties, one sub-node
126 containing trip nodes and one sub-node containing all the zone cooling maps.
129 - polling-delay: The maximum number of milliseconds to wait between polls
130 Type: unsigned when checking this thermal zone.
133 - polling-delay-passive: The maximum number of milliseconds to wait
134 Type: unsigned between polls when performing passive cooling.
137 - thermal-sensors: A list of thermal sensor phandles and sensor specifier
138 Type: list of used while monitoring the thermal zone.
142 - trips: A sub-node which is a container of only trip point nodes
143 Type: sub-node required to describe the thermal zone.
145 - cooling-maps: A sub-node which is a container of only cooling device
146 Type: sub-node map nodes, used to describe the relation between trips
150 - coefficients: An array of integers (one signed cell) containing
151 Type: array coefficients to compose a linear relation between
152 Elem size: one cell the sensors listed in the thermal-sensors property.
153 Elem type: signed Coefficients defaults to 1, in case this property
154 is not specified. A simple linear polynomial is used:
155 Z = c0 * x0 + c1 + x1 + ... + c(n-1) * x(n-1) + cn.
157 The coefficients are ordered and they match with sensors
158 by means of sensor ID. Additional coefficients are
159 interpreted as constant offset.
161 - sustainable-power: An estimate of the sustainable power (in mW) that the
162 Type: unsigned thermal zone can dissipate at the desired
163 Size: one cell control temperature. For reference, the
164 sustainable power of a 4'' phone is typically
165 2000mW, while on a 10'' tablet is around
168 Note: The delay properties are bound to the maximum dT/dt (temperature
169 derivative over time) in two situations for a thermal zone:
170 (i) - when passive cooling is activated (polling-delay-passive); and
171 (ii) - when the zone just needs to be monitored (polling-delay) or
172 when active cooling is activated.
174 The maximum dT/dt is highly bound to hardware power consumption and dissipation
175 capability. The delays should be chosen to account for said max dT/dt,
176 such that a device does not cross several trip boundaries unexpectedly
177 between polls. Choosing the right polling delays shall avoid having the
178 device in temperature ranges that may damage the silicon structures and
179 reduce silicon lifetime.
181 * The thermal-zones node
183 The "thermal-zones" node is a container for all thermal zone nodes. It shall
184 contain only sub-nodes describing thermal zones as in the section
185 "Thermal zone nodes". The "thermal-zones" node appears under "/".
189 Below are several examples on how to use thermal data descriptors
190 using device tree bindings:
192 (a) - CPU thermal zone
194 The CPU thermal zone example below describes how to setup one thermal zone
195 using one single sensor as temperature source and many cooling devices and
196 power dissipation control sources.
198 #include <dt-bindings/thermal/thermal.h>
202 * Here is an example of describing a cooling device for a DVFS
203 * capable CPU. The CPU node describes its four OPPs.
204 * The cooling states possible are 0..3, and they are
205 * used as OPP indexes. The minimum cooling state is 0, which means
206 * all four OPPs can be available to the system. The maximum
207 * cooling state is 3, which means only the lowest OPPs (198MHz@0.85V)
208 * can be available in the system.
219 #cooling-cells = <2>; /* min followed by max */
227 * A simple fan controller which supports 10 speeds of operation
228 * (represented as 0-9).
232 #cooling-cells = <2>; /* min followed by max */
239 * A simple IC with a single bandgap temperature sensor.
241 bandgap0: bandgap@0000ed00 {
243 #thermal-sensor-cells = <0>;
248 cpu_thermal: cpu-thermal {
249 polling-delay-passive = <250>; /* milliseconds */
250 polling-delay = <1000>; /* milliseconds */
252 thermal-sensors = <&bandgap0>;
255 cpu_alert0: cpu-alert0 {
256 temperature = <90000>; /* millicelsius */
257 hysteresis = <2000>; /* millicelsius */
260 cpu_alert1: cpu-alert1 {
261 temperature = <100000>; /* millicelsius */
262 hysteresis = <2000>; /* millicelsius */
266 temperature = <125000>; /* millicelsius */
267 hysteresis = <2000>; /* millicelsius */
274 trip = <&cpu_alert0>;
275 cooling-device = <&fan0 THERMAL_NO_LIMIT 4>;
278 trip = <&cpu_alert1>;
279 cooling-device = <&fan0 5 THERMAL_NO_LIMIT>;
282 trip = <&cpu_alert1>;
284 <&cpu0 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
290 In the example above, the ADC sensor (bandgap0) at address 0x0000ED00 is
291 used to monitor the zone 'cpu-thermal' using its sole sensor. A fan
292 device (fan0) is controlled via I2C bus 1, at address 0x48, and has ten
293 different cooling states 0-9. It is used to remove the heat out of
294 the thermal zone 'cpu-thermal' using its cooling states
295 from its minimum to 4, when it reaches trip point 'cpu_alert0'
296 at 90C, as an example of active cooling. The same cooling device is used at
297 'cpu_alert1', but from 5 to its maximum state. The cpu@0 device is also
298 linked to the same thermal zone, 'cpu-thermal', as a passive cooling device,
299 using all its cooling states at trip point 'cpu_alert1',
300 which is a trip point at 100C. On the thermal zone 'cpu-thermal', at the
301 temperature of 125C, represented by the trip point 'cpu_crit', the silicon
302 is not reliable anymore.
304 (b) - IC with several internal sensors
306 The example below describes how to deploy several thermal zones based off a
307 single sensor IC, assuming it has several internal sensors. This is a common
308 case on SoC designs with several internal IPs that may need different thermal
309 requirements, and thus may have their own sensor to monitor or detect internal
310 hotspots in their silicon.
312 #include <dt-bindings/thermal/thermal.h>
317 * A simple IC with several bandgap temperature sensors.
319 bandgap0: bandgap@0000ed00 {
321 #thermal-sensor-cells = <1>;
326 cpu_thermal: cpu-thermal {
327 polling-delay-passive = <250>; /* milliseconds */
328 polling-delay = <1000>; /* milliseconds */
331 thermal-sensors = <&bandgap0 0>;
334 /* each zone within the SoC may have its own trips */
335 cpu_alert: cpu-alert {
336 temperature = <100000>; /* millicelsius */
337 hysteresis = <2000>; /* millicelsius */
341 temperature = <125000>; /* millicelsius */
342 hysteresis = <2000>; /* millicelsius */
348 /* each zone within the SoC may have its own cooling */
353 gpu_thermal: gpu-thermal {
354 polling-delay-passive = <120>; /* milliseconds */
355 polling-delay = <1000>; /* milliseconds */
358 thermal-sensors = <&bandgap0 1>;
361 /* each zone within the SoC may have its own trips */
362 gpu_alert: gpu-alert {
363 temperature = <90000>; /* millicelsius */
364 hysteresis = <2000>; /* millicelsius */
368 temperature = <105000>; /* millicelsius */
369 hysteresis = <2000>; /* millicelsius */
375 /* each zone within the SoC may have its own cooling */
380 dsp_thermal: dsp-thermal {
381 polling-delay-passive = <50>; /* milliseconds */
382 polling-delay = <1000>; /* milliseconds */
385 thermal-sensors = <&bandgap0 2>;
388 /* each zone within the SoC may have its own trips */
389 dsp_alert: dsp-alert {
390 temperature = <90000>; /* millicelsius */
391 hysteresis = <2000>; /* millicelsius */
395 temperature = <135000>; /* millicelsius */
396 hysteresis = <2000>; /* millicelsius */
402 /* each zone within the SoC may have its own cooling */
408 In the example above, there is one bandgap IC which has the capability to
409 monitor three sensors. The hardware has been designed so that sensors are
410 placed on different places in the DIE to monitor different temperature
411 hotspots: one for CPU thermal zone, one for GPU thermal zone and the
412 other to monitor a DSP thermal zone.
414 Thus, there is a need to assign each sensor provided by the bandgap IC
415 to different thermal zones. This is achieved by means of using the
416 #thermal-sensor-cells property and using the first cell of the sensor
417 specifier as sensor ID. In the example, then, <bandgap 0> is used to
418 monitor CPU thermal zone, <bandgap 1> is used to monitor GPU thermal
419 zone and <bandgap 2> is used to monitor DSP thermal zone. Each zone
420 may be uncorrelated, having its own dT/dt requirements, trips
424 (c) - Several sensors within one single thermal zone
426 The example below illustrates how to use more than one sensor within
429 #include <dt-bindings/thermal/thermal.h>
434 * A simple IC with a single temperature sensor.
438 #thermal-sensor-cells = <0>;
445 * A simple IC with a single bandgap temperature sensor.
447 bandgap0: bandgap@0000ed00 {
449 #thermal-sensor-cells = <0>;
454 cpu_thermal: cpu-thermal {
455 polling-delay-passive = <250>; /* milliseconds */
456 polling-delay = <1000>; /* milliseconds */
458 thermal-sensors = <&bandgap0>, /* cpu */
459 <&adc>; /* pcb north */
461 /* hotspot = 100 * bandgap - 120 * adc + 484 */
462 coefficients = <100 -120 484>;
474 In some cases, there is a need to use more than one sensor to extrapolate
475 a thermal hotspot in the silicon. The above example illustrates this situation.
476 For instance, it may be the case that a sensor external to CPU IP may be placed
477 close to CPU hotspot and together with internal CPU sensor, it is used
478 to determine the hotspot. Assuming this is the case for the above example,
479 the hypothetical extrapolation rule would be:
480 hotspot = 100 * bandgap - 120 * adc + 484
482 In other context, the same idea can be used to add fixed offset. For instance,
483 consider the hotspot extrapolation rule below:
484 hotspot = 1 * adc + 6000
486 In the above equation, the hotspot is always 6C higher than what is read
487 from the ADC sensor. The binding would be then:
488 thermal-sensors = <&adc>;
490 /* hotspot = 1 * adc + 6000 */
491 coefficients = <1 6000>;
495 The board thermal example below illustrates how to setup one thermal zone
496 with many sensors and many cooling devices.
498 #include <dt-bindings/thermal/thermal.h>
503 * An IC with several temperature sensor.
505 adc_dummy: sensor@50 {
507 #thermal-sensor-cells = <1>; /* sensor internal ID */
513 polling-delay-passive = <500>; /* milliseconds */
514 polling-delay = <2500>; /* milliseconds */
517 thermal-sensors = <&adc_dummy 4>;
528 board_thermal: board-thermal {
529 polling-delay-passive = <1000>; /* milliseconds */
530 polling-delay = <2500>; /* milliseconds */
533 thermal-sensors = <&adc_dummy 0>, /* pcb top edge */
534 <&adc_dummy 1>, /* lcd */
535 <&adc_dummy 2>; /* back cover */
537 * An array of coefficients describing the sensor
538 * linear relation. E.g.:
539 * z = c1*x1 + c2*x2 + c3*x3
541 coefficients = <1200 -345 890>;
543 sustainable-power = <2500>;
546 /* Trips are based on resulting linear equation */
548 temperature = <60000>; /* millicelsius */
549 hysteresis = <2000>; /* millicelsius */
553 temperature = <55000>; /* millicelsius */
554 hysteresis = <2000>; /* millicelsius */
558 temperature = <53000>; /* millicelsius */
559 hysteresis = <2000>; /* millicelsius */
562 crit_trip: crit-trip {
563 temperature = <68000>; /* millicelsius */
564 hysteresis = <2000>; /* millicelsius */
572 cooling-device = <&cpu0 0 2>;
577 cooling-device = <&gpu0 0 2>;
582 cooling-device = <&lcd0 5 10>;
589 The above example is a mix of previous examples, a sensor IP with several internal
590 sensors used to monitor different zones, one of them is composed by several sensors and
591 with different cooling devices.