Re: [PATCH v2 02/11] dt-bindings: hwmon: Add Apple System Management Controller hwmon schema
From: Rob Herring <robh@kernel.org>
Date: 2025-08-29 16:40:58
Also in:
asahi, linux-devicetree, linux-hwmon, linux-input, linux-rtc, lkml
On Wed, Aug 27, 2025 at 09:22:36PM +1000, James Calligeros wrote:
quoted hunk ↗ jump to hunk
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 | 132 +++++++++++++++++++++++++ .../bindings/mfd/apple,smc.yaml | 36 +++++++ MAINTAINERS | 1 + 3 files changed, 169 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..08cc4f55f3a41ca8b3b428088f96240266fa42e8 --- /dev/null +++ b/Documentation/devicetree/bindings/hwmon/apple,smc-hwmon.yaml@@ -0,0 +1,132 @@ +# 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> + +definitions:
$defs definitions was convention. $defs is in json-schema spec now.
+ apple,key-id:
+ $ref: /schemas/types.yaml#/definitions/string
+ pattern: "^[A-Za-z0-9]{4}$"
+ description: The SMC FourCC key of the desired sensor.
+ Must match the node's suffix.
+
+ label:
+ description: Human-readable name for the sensor
+
+properties:
+ compatible:
+ const: apple,smc-hwmon
+
+patternProperties:
+ "^current-[A-Za-z0-9]{4}$":
+ type: object
+ additionalProperties: false
+
+ properties:
+ apple,key-id:
+ $ref: "#/definitions/apple,key-id"
+
+ label:
+ $ref: "#/definitions/label"
+
+ required:
+ - apple,key-id
+ - label
This should be something like this:
"^current-[A-Za-z0-9]{4}$":
$ref: "#/$defs/sensor"
unevaluatedProperties: false
With the $defs/sensor being:
$defs:
sensor:
type: object
properties:
apple,key-id:
$ref: /schemas/types.yaml#/definitions/string
pattern: "^[A-Za-z0-9]{4}$"
description:
The SMC FourCC key of the desired sensor. Must match the
node's suffix.
label:
description: Human-readable name for the sensor
required:
- apple,key-id
- label
Though in general, 'label' should never be required being just for human
convenience.
+
+ "^fan-[A-Za-z0-9]{4}$":
+ type: object
+ additionalProperties: falseAnd this one the same as above, but with the additional fan properties listed here.
+
+ properties:
+ apple,key-id:
+ $ref: "#/definitions/apple,key-id"
+
+ apple,fan-minimum:
+ $ref: /schemas/types.yaml#/definitions/string
+ pattern: "^[A-Za-z0-9]{4}$"
+ description: SMC key containing the fan's minimum speed
+
+ apple,fan-maximum:
+ $ref: /schemas/types.yaml#/definitions/string
+ pattern: "^[A-Za-z0-9]{4}$"
+ description: SMC key containing the fan's maximum speed
+
+ 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 key to enable/disable manual fan control
+
+ label:
+ $ref: "#/definitions/label"
+
+ required:
+ - apple,key-id
+ - label
+
+ "^power-[A-Za-z0-9]{4}$":
+ type: object
+ additionalProperties: false
+
+ properties:
+ apple,key-id:
+ $ref: "#/definitions/apple,key-id"
+
+ label:
+ $ref: "#/definitions/label"
+
+ required:
+ - apple,key-id
+ - label
+
+ "^temperature-[A-Za-z0-9]{4}$":
+ type: object
+ additionalProperties: false
+
+ properties:
+ apple,key-id:
+ $ref: "#/definitions/apple,key-id"
+
+ label:
+ $ref: "#/definitions/label"
+
+ required:
+ - apple,key-id
+ - label
+
+ "^voltage-[A-Za-z0-9]{4}$":
+ type: object
+ additionalProperties: false
+
+ properties:
+ apple,key-id:
+ $ref: "#/definitions/apple,key-id"
+
+ label:
+ $ref: "#/definitions/label"
+
+ required:
+ - apple,key-id
+ - label
+
+additionalProperties: false