[PATCH 2/8] dt-bindings: hwmon: add Apple System Management Controller hwmon schema
From: James Calligeros <hidden>
Date: 2025-08-19 11:48:22
Also in:
asahi, linux-arm-kernel, linux-devicetree, linux-hwmon, linux-rtc, lkml
Subsystem:
arm/apple machine support, hardware monitoring, multifunction devices (mfd), open firmware and flattened device tree bindings, the rest · Maintainers:
Sven Peter, Janne Grunau, Guenter Roeck, Lee Jones, Rob Herring, Krzysztof Kozlowski, Conor Dooley, Linus Torvalds
Apple Silicon devices integrate a vast array of sensors, monitoring current, power, temperature, and voltage across almost every part of the system. The sensors themselves are all connected to the System Management Controller (SMC). The SMC firmware exposes the data reported by these sensors via its standard FourCC-based key-value API. The SMC is also responsible for monitoring and controlling any fans connected to the system, exposing them in the same way. For reasons known only to Apple, each device exposes its sensors with an almost totally unique set of keys. This is true even for devices which share an SoC. An M1 Mac mini, for example, will report its core temperatures on different keys to an M1 MacBook Pro. Worse still, the SMC does not provide a way to enumerate the available keys at runtime, nor do the keys follow any sort of reasonable or consistent naming rules that could be used to deduce their purpose. We must therefore know which keys are present on any given device, and which function they serve, ahead of time. Add a schema so that we can describe the available sensors for a given Apple Silicon device in the Devicetree. Signed-off-by: James Calligeros <redacted> --- .../bindings/hwmon/apple,smc-hwmon.yaml | 148 +++++++++++++++++++++++++ .../bindings/mfd/apple,smc.yaml | 45 ++++++++ 2 files changed, 193 insertions(+)
diff --git a/Documentation/devicetree/bindings/hwmon/apple,smc-hwmon.yaml b/Documentation/devicetree/bindings/hwmon/apple,smc-hwmon.yaml
new file mode 100644
index 0000000000000000000000000000000000000000..3ebc0463be4e1ce54005418feaa87ec7254dab6e
--- /dev/null
+++ b/Documentation/devicetree/bindings/hwmon/apple,smc-hwmon.yaml@@ -0,0 +1,148 @@ +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) +%YAML 1.2 +--- +$id: http://devicetree.org/schemas/hwmon/apple,smc-hwmon.yaml# +$schema: http://devicetree.org/meta-schemas/core.yaml# + +title: Apple SMC Hardware Monitoring + +description: + Apple's System Management Controller (SMC) exposes a vast array of + hardware monitoring sensors, including temperature probes, current and + voltage sense, power meters, and fan speeds. It also provides endpoints + to manually control the speed of each fan individually. Each Apple + Silicon device exposes a different set of endpoints via SMC keys. This + is true even when two machines share an SoC. The CPU core temperature + sensor keys on an M1 Mac mini are different to those on an M1 MacBook + Pro, for example. + +maintainers: + - James Calligeros <jcalligeros99@gmail.com> + +properties: + compatible: + const: apple,smc-hwmon + + current: + description: SMC current sense endpoints + type: object + additionalProperties: false + patternProperties: + "^current-[A-Za-z0-9]{4}": + type: object + additionalProperties: false + required: + - apple,key-id + properties: + apple,key-id: + $ref: /schemas/types.yaml#/definitions/string + pattern: "^[A-Za-z0-9]{4}" + description: The SMC FourCC key of the desired current sensor. + Should match the node's suffix, but doesn't have to. + label: + $ref: /schemas/types.yaml#/definitions/string + description: Human-readable name for the sensor + + fan: + description: SMC fan control endpoints. A fan is made up of five + SMC keys - the fan's current speed, its minimum speed, its maximum + speed, a writeable target speed, and a writeable mode. The SMC will + automatically manage system fans unless a 1 is written to the fan's + mode key. + type: object + additionalProperties: false + patternProperties: + "^fan-[A-Za-z0-9]{4}": + type: object + additionalProperties: false + required: + - apple,key-id + properties: + apple,key-id: + $ref: /schemas/types.yaml#/definitions/string + pattern: "^[A-Za-z0-9]{4}" + description: The SMC FourCC key of the desired fan. This is the + main key, which reports the fan's current speed. Sould match + the node's suffix, but doesn't have to. + apple,fan-minimum: + $ref: /schemas/types.yaml#/definitions/string + pattern: "^[A-Za-z0-9]{4}" + description: The minimum speed the current fan can run at + apple,fan-maximum: + $ref: /schemas/types.yaml#/definitions/string + pattern: "^[A-Za-z0-9]{4}" + description: The maximum speed the current fan can run at + apple,fan-target: + $ref: /schemas/types.yaml#/definitions/string + pattern: "^[A-Za-z0-9]{4}" + description: Writeable endpoint for setting desired fan speed + apple,fan-mode: + $ref: /schemas/types.yaml#/definitions/string + pattern: "^[A-Za-z0-9]{4}" + description: Writeable endpoint to enable/disable manual fan + control + label: + $ref: /schemas/types.yaml#/definitions/string + description: Human-readable name for the sensor + + power: + description: SMC power meter endpoints + type: object + additionalProperties: false + patternProperties: + "^power-[A-Za-z0-9]{4}": + type: object + additionalProperties: false + required: + - apple,key-id + properties: + apple,key-id: + $ref: /schemas/types.yaml#/definitions/string + pattern: "^[A-Za-z0-9]{4}" + description: The SMC FourCC key of the desired power meter. + Should match the node's suffix, but doesn't have to. + label: + $ref: /schemas/types.yaml#/definitions/string + description: Human-readable name for the sensor + + temperature: + description: SMC temperature sensor endpoints + type: object + additionalProperties: false + patternProperties: + "^temperature-[A-Za-z0-9]{4}": + type: object + additionalProperties: false + required: + - apple,key-id + properties: + apple,key-id: + $ref: /schemas/types.yaml#/definitions/string + pattern: "^[A-Za-z0-9]{4}" + description: The SMC FourCC key of the desired temperature + sensor. Should match the node's suffix, but doesn't have to. + label: + $ref: /schemas/types.yaml#/definitions/string + description: Human-readable name for the sensor + + voltage: + description: SMC voltage sensor endpoints + type: object + additionalProperties: false + patternProperties: + "^voltage-[A-Za-z0-9]{4}": + type: object + additionalProperties: false + required: + - apple,key-id + properties: + apple,key-id: + $ref: /schemas/types.yaml#/definitions/string + pattern: "^[A-Za-z0-9]{4}" + description: The SMC FourCC key of the desired voltage + sensor. Should match the node's suffix, but doesn't have to. + label: + $ref: /schemas/types.yaml#/definitions/string + description: Human-readable name for the sensor + +additionalProperties: false
diff --git a/Documentation/devicetree/bindings/mfd/apple,smc.yaml b/Documentation/devicetree/bindings/mfd/apple,smc.yaml
index 38f077867bdeedba8a486a63e366e9c943a75681..370928bb42010edca17839faf0bda4630611a7a2 100644
--- a/Documentation/devicetree/bindings/mfd/apple,smc.yaml
+++ b/Documentation/devicetree/bindings/mfd/apple,smc.yaml@@ -44,6 +44,9 @@ properties: rtc: $ref: /schemas/rtc/apple,smc-rtc.yaml + hwmon: + $ref: /schemas/hwmon/apple,smc-hwmon.yaml + additionalProperties: false required:
@@ -84,5 +87,47 @@ examples: nvmem-cells = <&rtc_offset>; nvmem-cell-names = "rtc_offset"; }; + + hwmon { + compatible = "apple,smc-hwmon"; + current { + current-ID0R { + apple,key-id = "ID0R"; + label = "AC Input Current"; + }; + }; + + fan { + fan-F0Ac { + apple,key-id = "F0Ac"; + apple,fan-minimum = "F0Mn"; + apple,fan-maximum = "F0Mx"; + apple,fan-target = "F0Tg"; + apple,fan-mode = "F0Md"; + label = "Fan 1"; + }; + }; + + power { + power-PSTR { + apple,key-id = "PSTR"; + label = "Total System Power"; + }; + }; + + temperature { + temperature-TW0P { + apple,key-id = "TW0P"; + label = "WiFi/BT Module Temperature"; + }; + }; + + voltage { + voltage-VD0R { + apple,key-id = "VD0R"; + label = "AC Input Voltage"; + }; + }; + }; }; };
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2.50.1