Re: [PATCH v3 3/3] dt-bindings: thermal: Add yaml bindings for thermal zones
From: Lukasz Luba
Date: Wed Mar 25 2020 - 07:06:33 EST
On 3/25/20 6:34 AM, Amit Kucheria wrote:
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@xxxxxxxxxx>
---
Changes since v2:
- Addressed review comment from Rob
- Added required properties for thermal-zones node
- Added select: true to thermal-cooling-devices.yaml
- Fixed up example to pass dt_binding_check
.../bindings/thermal/thermal-zones.yaml | 324 ++++++++++++++++++
1 file changed, 324 insertions(+)
create mode 100644 Documentation/devicetree/bindings/thermal/thermal-zones.yaml
diff --git a/Documentation/devicetree/bindings/thermal/thermal-zones.yaml b/Documentation/devicetree/bindings/thermal/thermal-zones.yaml
new file mode 100644
index 000000000000..5632304dcf62
--- /dev/null
+++ b/Documentation/devicetree/bindings/thermal/thermal-zones.yaml
@@ -0,0 +1,324 @@
+# 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@xxxxxxxxxx>
+
+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:
+ $nodename:
+ const: thermal-zones
+ description:
+ A /thermal-zones node is required in order to use the thermal framework to
+ manage input from the various thermal zones in the system in order to
+ mitigate thermal overload conditions. It does not represent a real device
+ in the system, but acts as a container to link thermal sensor devices,
I would say 'thermal sensor device', since there is 1-to-1 mapping and
aggregating a few sensors inside one tz is not allowed (or I missed
some patches queuing).
+ platform-data regarding temperature thresholds and the mitigation actions
+ to take when the temperature crosses those thresholds.
+
+patternProperties:
+ "^[a-zA-Z][a-zA-Z0-9\\-]{1,12}-thermal$":
+ 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:
+ $ref: /schemas/types.yaml#/definitions/phandle-array
+ description:
+ A list of thermal sensor phandles and sensor specifiers used to
+ monitor this thermal zone.
I don't know why it's not consistent with the actual code in
of-thermal.c, where there is even a comment stated:
/* For now, thermal framework supports only 1 sensor per zone */
I think this is the place where developers should be informed about
the limitation and not even try to put more sensors into the list.
+
+ trips:
+ type: object
+ description:
+ This node describes a set of points in the temperature domain at
+ which the thermal framework needs to takes action. The actions to
s/needs to takes/needs to take/
+ be taken are defined in another node called cooling-maps.
+
+ patternProperties:
+ "^[a-zA-Z][a-zA-Z0-9\\-_]{0,63}$":
+ 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.
This property is worth a bit longer description.
+
+ 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.
[snip]
+
+ 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>;
+ cooling-device = <&CPU0 THERMAL_NO_LIMIT
+ THERMAL_NO_LIMIT>,
+ <&CPU1 THERMAL_NO_LIMIT
+ THERMAL_NO_LIMIT>,
+ <&CPU2 THERMAL_NO_LIMIT
+ THERMAL_NO_LIMIT>,
+ <&CPU3 THERMAL_NO_LIMIT
+ THERMAL_NO_LIMIT>;
+ };
+
+ map1 {
+ trip = <&cpu0_alert1>;
+ cooling-device = <&CPU0 THERMAL_NO_LIMIT
+ THERMAL_NO_LIMIT>,
+ <&CPU1 THERMAL_NO_LIMIT
+ THERMAL_NO_LIMIT>,
+ <&CPU2 THERMAL_NO_LIMIT
+ THERMAL_NO_LIMIT>,
+ <&CPU3 THERMAL_NO_LIMIT
+ THERMAL_NO_LIMIT>;
From this two examples of handling cpu0_alert0 and cpu0_alert1 you
cannot conclude anything (if you don't understand thermal framework (and
probably IPA). As a simple example it would be better to put a comment
with a description and limit min, max to a specific OPP:
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>;
};
IMHO this kind of example would tell more to an avg driver developer.
Regards,
Lukasz