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dt-bindings: thermal: Add yaml bindings for thermal zones
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As part of moving the thermal bindings to YAML, split it up into 3
bindings: thermal sensors, cooling devices and thermal zones.

The thermal-zone binding is a software abstraction to capture the
properties of each zone - how often they should be checked, the
temperature thresholds (trips) at which mitigation actions need to be
taken and the level of mitigation needed at those thresholds.

Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/44e5c68bc654ccaf88945f70dc875fa186dd1480.1585748882.git.amit.kucheria@linaro.org
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# 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 binding

maintainers:
- Amit Kucheria <amitk@kernel.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.

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
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
minimum: 0
maximum: 100
description:
The percentage contribution of the cooling devices at the
specific trip temperature referenced in this map
to this thermal zone

required:
- trip
- cooling-device
additionalProperties: false

required:
- polling-delay
- polling-delay-passive
- thermal-sensors
- trips
additionalProperties: false

examples:
- |
#include <dt-bindings/interrupt-controller/arm-gic.h>
#include <dt-bindings/thermal/thermal.h>
// Example 1: SDM845 TSENS
soc: soc@0 {
#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";
};
};
};
};
...

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