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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
7 binding descriptors.
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
16 measurements.
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.
32 Required property:
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 (as referred to be the cooling-min-state and cooling-max-state
59 properties) should be defined in a particular device's binding.
60 For more examples of cooling devices, refer to the example sections below.
62 Required properties:
63 - cooling-min-state: An integer indicating the smallest
64 Type: unsigned cooling state accepted. Typically 0.
65 Size: one cell
67 - cooling-max-state: An integer indicating the largest
68 Type: unsigned cooling state accepted.
69 Size: one cell
71 - #cooling-cells: Used to provide cooling device specific information
72 Type: unsigned while referring to it. Must be at least 2, in order
73 Size: one cell to specify minimum and maximum cooling state used
74 in the reference. The first cell is the minimum
75 cooling state requested and the second cell is
76 the maximum cooling state requested in the reference.
77 See Cooling device maps section below for more details
78 on how consumers refer to cooling devices.
80 * Trip points
82 The trip node is a node to describe a point in the temperature domain
83 in which the system takes an action. This node describes just the point,
84 not the action.
86 Required properties:
87 - temperature: An integer indicating the trip temperature level,
88 Type: signed in millicelsius.
89 Size: one cell
91 - hysteresis: A low hysteresis value on temperature property (above).
92 Type: unsigned This is a relative value, in millicelsius.
93 Size: one cell
95 - type: a string containing the trip type. Expected values are:
96 "active": A trip point to enable active cooling
97 "passive": A trip point to enable passive cooling
98 "hot": A trip point to notify emergency
99 "critical": Hardware not reliable.
100 Type: string
102 * Cooling device maps
104 The cooling device maps node is a node to describe how cooling devices
105 get assigned to trip points of the zone. The cooling devices are expected
106 to be loaded in the target system.
108 Required properties:
109 - cooling-device: A phandle of a cooling device with its specifier,
110 Type: phandle + referring to which cooling device is used in this
111 cooling specifier binding. In the cooling specifier, the first cell
112 is the minimum cooling state and the second cell
113 is the maximum cooling state used in this map.
114 - trip: A phandle of a trip point node within the same thermal
115 Type: phandle of zone.
116 trip point node
118 Optional property:
119 - contribution: The cooling contribution to the thermal zone of the
120 Type: unsigned referred cooling device at the referred trip point.
121 Size: one cell The contribution is a ratio of the sum
122 of all cooling contributions within a thermal zone.
124 Note: Using the THERMAL_NO_LIMIT (-1UL) constant in the cooling-device phandle
125 limit specifier means:
126 (i) - minimum state allowed for minimum cooling state used in the reference.
127 (ii) - maximum state allowed for maximum cooling state used in the reference.
128 Refer to include/dt-bindings/thermal/thermal.h for definition of this constant.
130 * Thermal zone nodes
132 The thermal zone node is the node containing all the required info
133 for describing a thermal zone, including its cooling device bindings. The
134 thermal zone node must contain, apart from its own properties, one sub-node
135 containing trip nodes and one sub-node containing all the zone cooling maps.
137 Required properties:
138 - polling-delay: The maximum number of milliseconds to wait between polls
139 Type: unsigned when checking this thermal zone.
140 Size: one cell
142 - polling-delay-passive: The maximum number of milliseconds to wait
143 Type: unsigned between polls when performing passive cooling.
144 Size: one cell
146 - thermal-sensors: A list of thermal sensor phandles and sensor specifier
147 Type: list of used while monitoring the thermal zone.
148 phandles + sensor
149 specifier
151 - trips: A sub-node which is a container of only trip point nodes
152 Type: sub-node required to describe the thermal zone.
154 - cooling-maps: A sub-node which is a container of only cooling device
155 Type: sub-node map nodes, used to describe the relation between trips
156 and cooling devices.
158 Optional property:
159 - coefficients: An array of integers (one signed cell) containing
160 Type: array coefficients to compose a linear relation between
161 Elem size: one cell the sensors listed in the thermal-sensors property.
162 Elem type: signed Coefficients defaults to 1, in case this property
163 is not specified. A simple linear polynomial is used:
164 Z = c0 * x0 + c1 + x1 + ... + c(n-1) * x(n-1) + cn.
166 The coefficients are ordered and they match with sensors
167 by means of sensor ID. Additional coefficients are
168 interpreted as constant offset.
170 Note: The delay properties are bound to the maximum dT/dt (temperature
171 derivative over time) in two situations for a thermal zone:
172 (i) - when passive cooling is activated (polling-delay-passive); and
173 (ii) - when the zone just needs to be monitored (polling-delay) or
174 when active cooling is activated.
176 The maximum dT/dt is highly bound to hardware power consumption and dissipation
177 capability. The delays should be chosen to account for said max dT/dt,
178 such that a device does not cross several trip boundaries unexpectedly
179 between polls. Choosing the right polling delays shall avoid having the
180 device in temperature ranges that may damage the silicon structures and
181 reduce silicon lifetime.
183 * The thermal-zones node
185 The "thermal-zones" node is a container for all thermal zone nodes. It shall
186 contain only sub-nodes describing thermal zones as in the section
187 "Thermal zone nodes". The "thermal-zones" node appears under "/".
189 * Examples
191 Below are several examples on how to use thermal data descriptors
192 using device tree bindings:
194 (a) - CPU thermal zone
196 The CPU thermal zone example below describes how to setup one thermal zone
197 using one single sensor as temperature source and many cooling devices and
198 power dissipation control sources.
200 #include <dt-bindings/thermal/thermal.h>
202 cpus {
203 /*
204 * Here is an example of describing a cooling device for a DVFS
205 * capable CPU. The CPU node describes its four OPPs.
206 * The cooling states possible are 0..3, and they are
207 * used as OPP indexes. The minimum cooling state is 0, which means
208 * all four OPPs can be available to the system. The maximum
209 * cooling state is 3, which means only the lowest OPPs (198MHz@0.85V)
210 * can be available in the system.
211 */
212 cpu0: cpu@0 {
213 ...
214 operating-points = <
215 /* kHz uV */
216 970000 1200000
217 792000 1100000
218 396000 950000
219 198000 850000
220 >;
221 cooling-min-state = <0>;
222 cooling-max-state = <3>;
223 #cooling-cells = <2>; /* min followed by max */
224 };
225 ...
226 };
228 &i2c1 {
229 ...
230 /*
231 * A simple fan controller which supports 10 speeds of operation
232 * (represented as 0-9).
233 */
234 fan0: fan@0x48 {
235 ...
236 cooling-min-state = <0>;
237 cooling-max-state = <9>;
238 #cooling-cells = <2>; /* min followed by max */
239 };
240 };
242 ocp {
243 ...
244 /*
245 * A simple IC with a single bandgap temperature sensor.
246 */
247 bandgap0: bandgap@0x0000ED00 {
248 ...
249 #thermal-sensor-cells = <0>;
250 };
251 };
253 thermal-zones {
254 cpu_thermal: cpu-thermal {
255 polling-delay-passive = <250>; /* milliseconds */
256 polling-delay = <1000>; /* milliseconds */
258 thermal-sensors = <&bandgap0>;
260 trips {
261 cpu_alert0: cpu-alert0 {
262 temperature = <90000>; /* millicelsius */
263 hysteresis = <2000>; /* millicelsius */
264 type = "active";
265 };
266 cpu_alert1: cpu-alert1 {
267 temperature = <100000>; /* millicelsius */
268 hysteresis = <2000>; /* millicelsius */
269 type = "passive";
270 };
271 cpu_crit: cpu-crit {
272 temperature = <125000>; /* millicelsius */
273 hysteresis = <2000>; /* millicelsius */
274 type = "critical";
275 };
276 };
278 cooling-maps {
279 map0 {
280 trip = <&cpu_alert0>;
281 cooling-device = <&fan0 THERMAL_NO_LIMIT 4>;
282 };
283 map1 {
284 trip = <&cpu_alert1>;
285 cooling-device = <&fan0 5 THERMAL_NO_LIMIT>;
286 };
287 map2 {
288 trip = <&cpu_alert1>;
289 cooling-device =
290 <&cpu0 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
291 };
292 };
293 };
294 };
296 In the example above, the ADC sensor (bandgap0) at address 0x0000ED00 is
297 used to monitor the zone 'cpu-thermal' using its sole sensor. A fan
298 device (fan0) is controlled via I2C bus 1, at address 0x48, and has ten
299 different cooling states 0-9. It is used to remove the heat out of
300 the thermal zone 'cpu-thermal' using its cooling states
301 from its minimum to 4, when it reaches trip point 'cpu_alert0'
302 at 90C, as an example of active cooling. The same cooling device is used at
303 'cpu_alert1', but from 5 to its maximum state. The cpu@0 device is also
304 linked to the same thermal zone, 'cpu-thermal', as a passive cooling device,
305 using all its cooling states at trip point 'cpu_alert1',
306 which is a trip point at 100C. On the thermal zone 'cpu-thermal', at the
307 temperature of 125C, represented by the trip point 'cpu_crit', the silicon
308 is not reliable anymore.
310 (b) - IC with several internal sensors
312 The example below describes how to deploy several thermal zones based off a
313 single sensor IC, assuming it has several internal sensors. This is a common
314 case on SoC designs with several internal IPs that may need different thermal
315 requirements, and thus may have their own sensor to monitor or detect internal
316 hotspots in their silicon.
318 #include <dt-bindings/thermal/thermal.h>
320 ocp {
321 ...
322 /*
323 * A simple IC with several bandgap temperature sensors.
324 */
325 bandgap0: bandgap@0x0000ED00 {
326 ...
327 #thermal-sensor-cells = <1>;
328 };
329 };
331 thermal-zones {
332 cpu_thermal: cpu-thermal {
333 polling-delay-passive = <250>; /* milliseconds */
334 polling-delay = <1000>; /* milliseconds */
336 /* sensor ID */
337 thermal-sensors = <&bandgap0 0>;
339 trips {
340 /* each zone within the SoC may have its own trips */
341 cpu_alert: cpu-alert {
342 temperature = <100000>; /* millicelsius */
343 hysteresis = <2000>; /* millicelsius */
344 type = "passive";
345 };
346 cpu_crit: cpu-crit {
347 temperature = <125000>; /* millicelsius */
348 hysteresis = <2000>; /* millicelsius */
349 type = "critical";
350 };
351 };
353 cooling-maps {
354 /* each zone within the SoC may have its own cooling */
355 ...
356 };
357 };
359 gpu_thermal: gpu-thermal {
360 polling-delay-passive = <120>; /* milliseconds */
361 polling-delay = <1000>; /* milliseconds */
363 /* sensor ID */
364 thermal-sensors = <&bandgap0 1>;
366 trips {
367 /* each zone within the SoC may have its own trips */
368 gpu_alert: gpu-alert {
369 temperature = <90000>; /* millicelsius */
370 hysteresis = <2000>; /* millicelsius */
371 type = "passive";
372 };
373 gpu_crit: gpu-crit {
374 temperature = <105000>; /* millicelsius */
375 hysteresis = <2000>; /* millicelsius */
376 type = "critical";
377 };
378 };
380 cooling-maps {
381 /* each zone within the SoC may have its own cooling */
382 ...
383 };
384 };
386 dsp_thermal: dsp-thermal {
387 polling-delay-passive = <50>; /* milliseconds */
388 polling-delay = <1000>; /* milliseconds */
390 /* sensor ID */
391 thermal-sensors = <&bandgap0 2>;
393 trips {
394 /* each zone within the SoC may have its own trips */
395 dsp_alert: dsp-alert {
396 temperature = <90000>; /* millicelsius */
397 hysteresis = <2000>; /* millicelsius */
398 type = "passive";
399 };
400 dsp_crit: gpu-crit {
401 temperature = <135000>; /* millicelsius */
402 hysteresis = <2000>; /* millicelsius */
403 type = "critical";
404 };
405 };
407 cooling-maps {
408 /* each zone within the SoC may have its own cooling */
409 ...
410 };
411 };
412 };
414 In the example above, there is one bandgap IC which has the capability to
415 monitor three sensors. The hardware has been designed so that sensors are
416 placed on different places in the DIE to monitor different temperature
417 hotspots: one for CPU thermal zone, one for GPU thermal zone and the
418 other to monitor a DSP thermal zone.
420 Thus, there is a need to assign each sensor provided by the bandgap IC
421 to different thermal zones. This is achieved by means of using the
422 #thermal-sensor-cells property and using the first cell of the sensor
423 specifier as sensor ID. In the example, then, <bandgap 0> is used to
424 monitor CPU thermal zone, <bandgap 1> is used to monitor GPU thermal
425 zone and <bandgap 2> is used to monitor DSP thermal zone. Each zone
426 may be uncorrelated, having its own dT/dt requirements, trips
427 and cooling maps.
430 (c) - Several sensors within one single thermal zone
432 The example below illustrates how to use more than one sensor within
433 one thermal zone.
435 #include <dt-bindings/thermal/thermal.h>
437 &i2c1 {
438 ...
439 /*
440 * A simple IC with a single temperature sensor.
441 */
442 adc: sensor@0x49 {
443 ...
444 #thermal-sensor-cells = <0>;
445 };
446 };
448 ocp {
449 ...
450 /*
451 * A simple IC with a single bandgap temperature sensor.
452 */
453 bandgap0: bandgap@0x0000ED00 {
454 ...
455 #thermal-sensor-cells = <0>;
456 };
457 };
459 thermal-zones {
460 cpu_thermal: cpu-thermal {
461 polling-delay-passive = <250>; /* milliseconds */
462 polling-delay = <1000>; /* milliseconds */
464 thermal-sensors = <&bandgap0>, /* cpu */
465 <&adc>; /* pcb north */
467 /* hotspot = 100 * bandgap - 120 * adc + 484 */
468 coefficients = <100 -120 484>;
470 trips {
471 ...
472 };
474 cooling-maps {
475 ...
476 };
477 };
478 };
480 In some cases, there is a need to use more than one sensor to extrapolate
481 a thermal hotspot in the silicon. The above example illustrates this situation.
482 For instance, it may be the case that a sensor external to CPU IP may be placed
483 close to CPU hotspot and together with internal CPU sensor, it is used
484 to determine the hotspot. Assuming this is the case for the above example,
485 the hypothetical extrapolation rule would be:
486 hotspot = 100 * bandgap - 120 * adc + 484
488 In other context, the same idea can be used to add fixed offset. For instance,
489 consider the hotspot extrapolation rule below:
490 hotspot = 1 * adc + 6000
492 In the above equation, the hotspot is always 6C higher than what is read
493 from the ADC sensor. The binding would be then:
494 thermal-sensors = <&adc>;
496 /* hotspot = 1 * adc + 6000 */
497 coefficients = <1 6000>;
499 (d) - Board thermal
501 The board thermal example below illustrates how to setup one thermal zone
502 with many sensors and many cooling devices.
504 #include <dt-bindings/thermal/thermal.h>
506 &i2c1 {
507 ...
508 /*
509 * An IC with several temperature sensor.
510 */
511 adc_dummy: sensor@0x50 {
512 ...
513 #thermal-sensor-cells = <1>; /* sensor internal ID */
514 };
515 };
517 thermal-zones {
518 batt-thermal {
519 polling-delay-passive = <500>; /* milliseconds */
520 polling-delay = <2500>; /* milliseconds */
522 /* sensor ID */
523 thermal-sensors = <&adc_dummy 4>;
525 trips {
526 ...
527 };
529 cooling-maps {
530 ...
531 };
532 };
534 board_thermal: board-thermal {
535 polling-delay-passive = <1000>; /* milliseconds */
536 polling-delay = <2500>; /* milliseconds */
538 /* sensor ID */
539 thermal-sensors = <&adc_dummy 0>, /* pcb top edge */
540 <&adc_dummy 1>, /* lcd */
541 <&adc_dummy 2>; /* back cover */
542 /*
543 * An array of coefficients describing the sensor
544 * linear relation. E.g.:
545 * z = c1*x1 + c2*x2 + c3*x3
546 */
547 coefficients = <1200 -345 890>;
549 trips {
550 /* Trips are based on resulting linear equation */
551 cpu_trip: cpu-trip {
552 temperature = <60000>; /* millicelsius */
553 hysteresis = <2000>; /* millicelsius */
554 type = "passive";
555 };
556 gpu_trip: gpu-trip {
557 temperature = <55000>; /* millicelsius */
558 hysteresis = <2000>; /* millicelsius */
559 type = "passive";
560 }
561 lcd_trip: lcp-trip {
562 temperature = <53000>; /* millicelsius */
563 hysteresis = <2000>; /* millicelsius */
564 type = "passive";
565 };
566 crit_trip: crit-trip {
567 temperature = <68000>; /* millicelsius */
568 hysteresis = <2000>; /* millicelsius */
569 type = "critical";
570 };
571 };
573 cooling-maps {
574 map0 {
575 trip = <&cpu_trip>;
576 cooling-device = <&cpu0 0 2>;
577 contribution = <55>;
578 };
579 map1 {
580 trip = <&gpu_trip>;
581 cooling-device = <&gpu0 0 2>;
582 contribution = <20>;
583 };
584 map2 {
585 trip = <&lcd_trip>;
586 cooling-device = <&lcd0 5 10>;
587 contribution = <15>;
588 };
589 };
590 };
591 };
593 The above example is a mix of previous examples, a sensor IP with several internal
594 sensors used to monitor different zones, one of them is composed by several sensors and
595 with different cooling devices.