1 # SPDX-License-Identifier: (GPL-2.0)
2 # Copyright 2020 Linaro Ltd.
3 %YAML 1.2
4 ---
5 $id: http://devicetree.org/schemas/thermal/thermal-zones.yaml#
6 $schema: http://devicetree.org/meta-schemas/base.yaml#
7
8 title: Thermal zone
9
10 maintainers:
11 - Daniel Lezcano <daniel.lezcano@linaro.org>
12
13 description: |
14 Thermal management is achieved in devicetree by describing the sensor hardware
15 and the software abstraction of cooling devices and thermal zones required to
16 take appropriate action to mitigate thermal overloads.
17
18 The following node types are used to completely describe a thermal management
19 system in devicetree:
20 - thermal-sensor: device that measures temperature, has SoC-specific bindings
21 - cooling-device: device used to dissipate heat either passively or actively
22 - thermal-zones: a container of the following node types used to describe all
23 thermal data for the platform
24
25 This binding describes the thermal-zones.
26
27 The polling-delay properties of a thermal-zone are bound to the maximum dT/dt
28 (temperature derivative over time) in two situations for a thermal zone:
29 1. when passive cooling is activated (polling-delay-passive)
30 2. when the zone just needs to be monitored (polling-delay) or when
31 active cooling is activated.
32
33 The maximum dT/dt is highly bound to hardware power consumption and
34 dissipation capability. The delays should be chosen to account for said
35 max dT/dt, such that a device does not cross several trip boundaries
36 unexpectedly between polls. Choosing the right polling delays shall avoid
37 having the device in temperature ranges that may damage the silicon structures
38 and reduce silicon lifetime.
39
40 properties:
41 $nodename:
42 const: thermal-zones
43 description:
44 A /thermal-zones node is required in order to use the thermal framework to
45 manage input from the various thermal zones in the system in order to
46 mitigate thermal overload conditions. It does not represent a real device
47 in the system, but acts as a container to link a thermal sensor device,
48 platform-data regarding temperature thresholds and the mitigation actions
49 to take when the temperature crosses those thresholds.
50
51 patternProperties:
52 # Node name is limited in size due to Linux kernel requirements - 19
53 # characters in total (see THERMAL_NAME_LENGTH, including terminating NUL
54 # byte):
55 "^[a-zA-Z][a-zA-Z0-9\\-]{1,10}-thermal$":
56 type: object
57 description:
58 Each thermal zone node contains information about how frequently it
59 must be checked, the sensor responsible for reporting temperature for
60 this zone, one sub-node containing the various trip points for this
61 zone and one sub-node containing all the zone cooling-maps.
62
63 properties:
64 polling-delay:
65 $ref: /schemas/types.yaml#/definitions/uint32
66 description:
67 The maximum number of milliseconds to wait between polls when
68 checking this thermal zone. Setting this to 0 disables the polling
69 timers setup by the thermal framework and assumes that the thermal
70 sensors in this zone support interrupts.
71
72 polling-delay-passive:
73 $ref: /schemas/types.yaml#/definitions/uint32
74 description:
75 The maximum number of milliseconds to wait between polls when
76 checking this thermal zone while doing passive cooling. Setting
77 this to 0 disables the polling timers setup by the thermal
78 framework and assumes that the thermal sensors in this zone
79 support interrupts.
80
81 critical-action:
82 $ref: /schemas/types.yaml#/definitions/string
83 description: |
84 The action the OS should perform after the critical temperature is reached.
85 By default the system will shutdown as a safe action to prevent damage
86 to the hardware, if the property is not set.
87 The shutdown action should be always the default and preferred one.
88 Choose 'reboot' with care, as the hardware may be in thermal stress,
89 thus leading to infinite reboots that may cause damage to the hardware.
90 Make sure the firmware/bootloader will act as the last resort and take
91 over the thermal control.
92
93 enum:
94 - shutdown
95 - reboot
96
97 thermal-sensors:
98 $ref: /schemas/types.yaml#/definitions/phandle-array
99 maxItems: 1
100 description:
101 The thermal sensor phandle and sensor specifier used to monitor this
102 thermal zone.
103
104 coefficients:
105 $ref: /schemas/types.yaml#/definitions/uint32-array
106 description:
107 An array of integers containing the coefficients of a linear equation
108 that binds all the sensors listed in this thermal zone.
109
110 The linear equation used is as follows,
111 z = c0 * x0 + c1 * x1 + ... + c(n-1) * x(n-1) + cn
112 where c0, c1, .., cn are the coefficients.
113
114 Coefficients default to 1 in case this property is not specified. The
115 coefficients are ordered and are matched with sensors by means of the
116 sensor ID. Additional coefficients are interpreted as constant offset.
117
118 sustainable-power:
119 $ref: /schemas/types.yaml#/definitions/uint32
120 description:
121 An estimate of the sustainable power (in mW) that this thermal zone
122 can dissipate at the desired control temperature. For reference, the
123 sustainable power of a 4-inch phone is typically 2000mW, while on a
124 10-inch tablet is around 4500mW.
125
126 trips:
127 type: object
128 description:
129 This node describes a set of points in the temperature domain at
130 which the thermal framework needs to take action. The actions to
131 be taken are defined in another node called cooling-maps.
132
133 patternProperties:
134 "^[a-zA-Z][a-zA-Z0-9\\-_]{0,63}$":
135 type: object
136
137 properties:
138 temperature:
139 $ref: /schemas/types.yaml#/definitions/int32
140 minimum: -273000
141 maximum: 200000
142 description:
143 An integer expressing the trip temperature in millicelsius.
144
145 hysteresis:
146 $ref: /schemas/types.yaml#/definitions/uint32
147 description:
148 An unsigned integer expressing the hysteresis delta with
149 respect to the trip temperature property above, also in
150 millicelsius. Any cooling action initiated by the framework is
151 maintained until the temperature falls below
152 (trip temperature - hysteresis). This potentially prevents a
153 situation where the trip gets constantly triggered soon after
154 cooling action is removed.
155
156 type:
157 $ref: /schemas/types.yaml#/definitions/string
158 enum:
159 - active # enable active cooling e.g. fans
160 - passive # enable passive cooling e.g. throttling cpu
161 - hot # send notification to driver
162 - critical # send notification to driver, trigger shutdown
163 description: |
164 There are four valid trip types: active, passive, hot,
165 critical.
166
167 The critical trip type is used to set the maximum
168 temperature threshold above which the HW becomes
169 unstable and underlying firmware might even trigger a
170 reboot. Hitting the critical threshold triggers a system
171 shutdown.
172
173 The hot trip type can be used to send a notification to
174 the thermal driver (if a .notify callback is registered).
175 The action to be taken is left to the driver.
176
177 The passive trip type can be used to slow down HW e.g. run
178 the CPU, GPU, bus at a lower frequency.
179
180 The active trip type can be used to control other HW to
181 help in cooling e.g. fans can be sped up or slowed down
182
183 required:
184 - temperature
185 - hysteresis
186 - type
187 additionalProperties: false
188
189 additionalProperties: false
190
191 cooling-maps:
192 type: object
193 additionalProperties: false
194 description:
195 This node describes the action to be taken when a thermal zone
196 crosses one of the temperature thresholds described in the trips
197 node. The action takes the form of a mapping relation between a
198 trip and the target cooling device state.
199
200 patternProperties:
201 "^map[-a-zA-Z0-9]*$":
202 type: object
203
204 properties:
205 trip:
206 $ref: /schemas/types.yaml#/definitions/phandle
207 description:
208 A phandle of a trip point node within this thermal zone.
209
210 cooling-device:
211 $ref: /schemas/types.yaml#/definitions/phandle-array
212 description:
213 A list of cooling device phandles along with the minimum
214 and maximum cooling state specifiers for each cooling
215 device. Using the THERMAL_NO_LIMIT (-1UL) constant in the
216 cooling-device phandle limit specifier lets the framework
217 use the minimum and maximum cooling state for that cooling
218 device automatically.
219
220 contribution:
221 $ref: /schemas/types.yaml#/definitions/uint32
222 description:
223 The cooling contribution to the thermal zone of the referred
224 cooling device at the referred trip point. The contribution is
225 a ratio of the sum of all cooling contributions within a
226 thermal zone.
227
228 required:
229 - trip
230 - cooling-device
231 additionalProperties: false
232
233 required:
234 - thermal-sensors
235
236 additionalProperties: false
237
238 additionalProperties: false
239
240 examples:
241 - |
242 #include <dt-bindings/interrupt-controller/arm-gic.h>
243 #include <dt-bindings/thermal/thermal.h>
244
245 // Example 1: SDM845 TSENS
246 soc {
247 #address-cells = <2>;
248 #size-cells = <2>;
249
250 /* ... */
251
252 tsens0: thermal-sensor@c263000 {
253 compatible = "qcom,sdm845-tsens", "qcom,tsens-v2";
254 reg = <0 0x0c263000 0 0x1ff>, /* TM */
255 <0 0x0c222000 0 0x1ff>; /* SROT */
256 #qcom,sensors = <13>;
257 interrupts = <GIC_SPI 506 IRQ_TYPE_LEVEL_HIGH>,
258 <GIC_SPI 508 IRQ_TYPE_LEVEL_HIGH>;
259 interrupt-names = "uplow", "critical";
260 #thermal-sensor-cells = <1>;
261 };
262
263 tsens1: thermal-sensor@c265000 {
264 compatible = "qcom,sdm845-tsens", "qcom,tsens-v2";
265 reg = <0 0x0c265000 0 0x1ff>, /* TM */
266 <0 0x0c223000 0 0x1ff>; /* SROT */
267 #qcom,sensors = <8>;
268 interrupts = <GIC_SPI 507 IRQ_TYPE_LEVEL_HIGH>,
269 <GIC_SPI 509 IRQ_TYPE_LEVEL_HIGH>;
270 interrupt-names = "uplow", "critical";
271 #thermal-sensor-cells = <1>;
272 };
273 };
274
275 /* ... */
276
277 thermal-zones {
278 cpu0-thermal {
279 polling-delay-passive = <250>;
280 polling-delay = <1000>;
281
282 thermal-sensors = <&tsens0 1>;
283
284 trips {
285 cpu0_alert0: trip-point0 {
286 temperature = <90000>;
287 hysteresis = <2000>;
288 type = "passive";
289 };
290
291 cpu0_alert1: trip-point1 {
292 temperature = <95000>;
293 hysteresis = <2000>;
294 type = "passive";
295 };
296
297 cpu0_crit: cpu_crit {
298 temperature = <110000>;
299 hysteresis = <1000>;
300 type = "critical";
301 };
302 };
303
304 cooling-maps {
305 map0 {
306 trip = <&cpu0_alert0>;
307 /* Corresponds to 1400MHz in OPP table */
308 cooling-device = <&CPU0 3 3>, <&CPU1 3 3>,
309 <&CPU2 3 3>, <&CPU3 3 3>;
310 };
311
312 map1 {
313 trip = <&cpu0_alert1>;
314 /* Corresponds to 1000MHz in OPP table */
315 cooling-device = <&CPU0 5 5>, <&CPU1 5 5>,
316 <&CPU2 5 5>, <&CPU3 5 5>;
317 };
318 };
319 };
320
321 /* ... */
322
323 cluster0-thermal {
324 polling-delay-passive = <250>;
325 polling-delay = <1000>;
326
327 thermal-sensors = <&tsens0 5>;
328
329 trips {
330 cluster0_alert0: trip-point0 {
331 temperature = <90000>;
332 hysteresis = <2000>;
333 type = "hot";
334 };
335 cluster0_crit: cluster0_crit {
336 temperature = <110000>;
337 hysteresis = <2000>;
338 type = "critical";
339 };
340 };
341 };
342
343 /* ... */
344
345 gpu-top-thermal {
346 polling-delay-passive = <250>;
347 polling-delay = <1000>;
348
349 thermal-sensors = <&tsens0 11>;
350
351 trips {
352 gpu1_alert0: trip-point0 {
353 temperature = <90000>;
354 hysteresis = <2000>;
355 type = "hot";
356 };
357 };
358 };
359 };
360 ...
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