path: root/Documentation/devicetree/bindings/thermal/thermal-zones.yaml

# SPDX-License-Identifier: (GPL-2.0)
# Copyright 2020 Linaro Ltd.
%YAML 1.2
---
$id: http://devicetree.org/schemas/thermal/thermal-zones.yaml#
$schema: http://devicetree.org/meta-schemas/base.yaml#

title: Thermal zone

maintainers:
  - Daniel Lezcano <daniel.lezcano@linaro.org>

description: |
  Thermal management is achieved in devicetree by describing the sensor hardware
  and the software abstraction of cooling devices and thermal zones required to
  take appropriate action to mitigate thermal overloads.

  The following node types are used to completely describe a thermal management
  system in devicetree:
   - thermal-sensor: device that measures temperature, has SoC-specific bindings
   - cooling-device: device used to dissipate heat either passively or actively
   - thermal-zones: a container of the following node types used to describe all
     thermal data for the platform

  This binding describes the thermal-zones.

  The polling-delay properties of a thermal-zone are bound to the maximum dT/dt
  (temperature derivative over time) in two situations for a thermal zone:
    1. when passive cooling is activated (polling-delay-passive)
    2. 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.

properties:
  $nodename:
    const: thermal-zones
    description:
      A /thermal-zones node is required in order to use the thermal framework to
      manage input from the various thermal zones in the system in order to
      mitigate thermal overload conditions. It does not represent a real device
      in the system, but acts as a container to link a thermal sensor device,
      platform-data regarding temperature thresholds and the mitigation actions
      to take when the temperature crosses those thresholds.

patternProperties:
  "^[a-zA-Z][a-zA-Z0-9\\-]{1,12}-thermal$":
    type: object
    description:
      Each thermal zone node contains information about how frequently it
      must be checked, the sensor responsible for reporting temperature for
      this zone, one sub-node containing the various trip points for this
      zone and one sub-node containing all the zone cooling-maps.

    properties:
      polling-delay:
        $ref: /schemas/types.yaml#/definitions/uint32
        description:
          The maximum number of milliseconds to wait between polls when
          checking this thermal zone. Setting this to 0 disables the polling
          timers setup by the thermal framework and assumes that the thermal
          sensors in this zone support interrupts.

      polling-delay-passive:
        $ref: /schemas/types.yaml#/definitions/uint32
        description:
          The maximum number of milliseconds to wait between polls when
          checking this thermal zone while doing passive cooling. Setting
          this to 0 disables the polling timers setup by the thermal
          framework and assumes that the thermal sensors in this zone
          support interrupts.

      critical-action:
        $ref: /schemas/types.yaml#/definitions/string
        description: |
          The action the OS should perform after the critical temperature is reached.
          By default the system will shutdown as a safe action to prevent damage
          to the hardware, if the property is not set.
          The shutdown action should be always the default and preferred one.
          Choose 'reboot' with care, as the hardware may be in thermal stress,
          thus leading to infinite reboots that may cause damage to the hardware.
          Make sure the firmware/bootloader will act as the last resort and take
          over the thermal control.

        enum:
          - shutdown
          - reboot

      thermal-sensors:
        $ref: /schemas/types.yaml#/definitions/phandle-array
        maxItems: 1
        description:
          The thermal sensor phandle and sensor specifier used to monitor this
          thermal zone.

      coefficients:
        $ref: /schemas/types.yaml#/definitions/uint32-array
        description:
          An array of integers containing the coefficients of a linear equation
          that binds all the sensors listed in this thermal zone.

          The linear equation used is as follows,
            z = c0 * x0 + c1 * x1 + ... + c(n-1) * x(n-1) + cn
          where c0, c1, .., cn are the coefficients.

          Coefficients default to 1 in case this property is not specified. The
          coefficients are ordered and are matched with sensors by means of the
          sensor ID. Additional coefficients are interpreted as constant offset.

      sustainable-power:
        $ref: /schemas/types.yaml#/definitions/uint32
        description:
          An estimate of the sustainable power (in mW) that this thermal zone
          can dissipate at the desired control temperature. For reference, the
          sustainable power of a 4-inch phone is typically 2000mW, while on a
          10-inch tablet is around 4500mW.

      trips:
        type: object
        description:
          This node describes a set of points in the temperature domain at
          which the thermal framework needs to take action. The actions to
          be taken are defined in another node called cooling-maps.

        patternProperties:
          "^[a-zA-Z][a-zA-Z0-9\\-_]{0,63}$":
            type: object

            properties:
              temperature:
                $ref: /schemas/types.yaml#/definitions/int32
                minimum: -273000
                maximum: 200000
                description:
                  An integer expressing the trip temperature in millicelsius.

              hysteresis:
                $ref: /schemas/types.yaml#/definitions/uint32
                description:
                  An unsigned integer expressing the hysteresis delta with
                  respect to the trip temperature property above, also in
                  millicelsius. Any cooling action initiated by the framework is
                  maintained until the temperature falls below
                  (trip temperature - hysteresis). This potentially prevents a
                  situation where the trip gets constantly triggered soon after
                  cooling action is removed.

              type:
                $ref: /schemas/types.yaml#/definitions/string
                enum:
                  - active   # enable active cooling e.g. fans
                  - passive  # enable passive cooling e.g. throttling cpu
                  - hot      # send notification to driver
                  - critical # send notification to driver, trigger shutdown
                description: |
                  There are four valid trip types: active, passive, hot,
                  critical.

                  The critical trip type is used to set the maximum
                  temperature threshold above which the HW becomes
                  unstable and underlying firmware might even trigger a
                  reboot. Hitting the critical threshold triggers a system
                  shutdown.

                  The hot trip type can be used to send a notification to
                  the thermal driver (if a .notify callback is registered).
                  The action to be taken is left to the driver.

                  The passive trip type can be used to slow down HW e.g. run
                  the CPU, GPU, bus at a lower frequency.

                  The active trip type can be used to control other HW to
                  help in cooling e.g. fans can be sped up or slowed down

            required:
              - temperature
              - hysteresis
              - type
            additionalProperties: false

        additionalProperties: false

      cooling-maps:
        type: object
        additionalProperties: false
        description:
          This node describes the action to be taken when a thermal zone
          crosses one of the temperature thresholds described in the trips
          node. The action takes the form of a mapping relation between a
          trip and the target cooling device state.

        patternProperties:
          "^map[-a-zA-Z0-9]*$":
            type: object

            properties:
              trip:
                $ref: /schemas/types.yaml#/definitions/phandle
                description:
                  A phandle of a trip point node within this thermal zone.

              cooling-device:
                $ref: /schemas/types.yaml#/definitions/phandle-array
                description:
                  A list of cooling device phandles along with the minimum
                  and maximum cooling state specifiers for each cooling
                  device. Using the THERMAL_NO_LIMIT (-1UL) constant in the
                  cooling-device phandle limit specifier lets the framework
                  use the minimum and maximum cooling state for that cooling
                  device automatically.

              contribution:
                $ref: /schemas/types.yaml#/definitions/uint32
                description:
                  The cooling contribution to the thermal zone of the referred
                  cooling device at the referred trip point. The contribution is
                  a ratio of the sum of all cooling contributions within a
                  thermal zone.

            required:
              - trip
              - cooling-device
            additionalProperties: false

    required:
      - thermal-sensors
      - trips

    additionalProperties: false

additionalProperties: false

examples:
  - |
    #include <dt-bindings/interrupt-controller/arm-gic.h>
    #include <dt-bindings/thermal/thermal.h>

    // Example 1: SDM845 TSENS
    soc {
            #address-cells = <2>;
            #size-cells = <2>;

            /* ... */

            tsens0: thermal-sensor@c263000 {
                    compatible = "qcom,sdm845-tsens", "qcom,tsens-v2";
                    reg = <0 0x0c263000 0 0x1ff>, /* TM */
                          <0 0x0c222000 0 0x1ff>; /* SROT */
                    #qcom,sensors = <13>;
                    interrupts = <GIC_SPI 506 IRQ_TYPE_LEVEL_HIGH>,
                                 <GIC_SPI 508 IRQ_TYPE_LEVEL_HIGH>;
                    interrupt-names = "uplow", "critical";
                    #thermal-sensor-cells = <1>;
            };

            tsens1: thermal-sensor@c265000 {
                    compatible = "qcom,sdm845-tsens", "qcom,tsens-v2";
                    reg = <0 0x0c265000 0 0x1ff>, /* TM */
                          <0 0x0c223000 0 0x1ff>; /* SROT */
                    #qcom,sensors = <8>;
                    interrupts = <GIC_SPI 507 IRQ_TYPE_LEVEL_HIGH>,
                                 <GIC_SPI 509 IRQ_TYPE_LEVEL_HIGH>;
                    interrupt-names = "uplow", "critical";
                    #thermal-sensor-cells = <1>;
            };
    };

    /* ... */

    thermal-zones {
            cpu0-thermal {
                    polling-delay-passive = <250>;
                    polling-delay = <1000>;

                    thermal-sensors = <&tsens0 1>;

                    trips {
                            cpu0_alert0: trip-point0 {
                                    temperature = <90000>;
                                    hysteresis = <2000>;
                                    type = "passive";
                            };

                            cpu0_alert1: trip-point1 {
                                    temperature = <95000>;
                                    hysteresis = <2000>;
                                    type = "passive";
                            };

                            cpu0_crit: cpu_crit {
                                    temperature = <110000>;
                                    hysteresis = <1000>;
                                    type = "critical";
                            };
                    };

                    cooling-maps {
                            map0 {
                                    trip = <&cpu0_alert0>;
                                    /* Corresponds to 1400MHz in OPP table */
                                    cooling-device = <&CPU0 3 3>, <&CPU1 3 3>,
                                                     <&CPU2 3 3>, <&CPU3 3 3>;
                            };

                            map1 {
                                    trip = <&cpu0_alert1>;
                                    /* Corresponds to 1000MHz in OPP table */
                                    cooling-device = <&CPU0 5 5>, <&CPU1 5 5>,
                                                     <&CPU2 5 5>, <&CPU3 5 5>;
                            };
                    };
            };

            /* ... */

            cluster0-thermal {
                    polling-delay-passive = <250>;
                    polling-delay = <1000>;

                    thermal-sensors = <&tsens0 5>;

                    trips {
                            cluster0_alert0: trip-point0 {
                                    temperature = <90000>;
                                    hysteresis = <2000>;
                                    type = "hot";
                            };
                            cluster0_crit: cluster0_crit {
                                    temperature = <110000>;
                                    hysteresis = <2000>;
                                    type = "critical";
                            };
                    };
            };

            /* ... */

            gpu-top-thermal {
                    polling-delay-passive = <250>;
                    polling-delay = <1000>;

                    thermal-sensors = <&tsens0 11>;

                    trips {
                            gpu1_alert0: trip-point0 {
                                    temperature = <90000>;
                                    hysteresis = <2000>;
                                    type = "hot";
                            };
                    };
            };
    };
...