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.
Reviewed-by: Neal Gompa <neal@gompa.dev>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: James Calligeros <jcalligeros99@gmail.com>
---
.../bindings/hwmon/apple,smc-hwmon.yaml | 86 +++++++++++++++++++++++++
.../bindings/mfd/apple,smc.yaml | 36 +++++++++++
MAINTAINERS | 1 +
3 files changed, 123 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 000000000000..2eec317bc4b3
--- /dev/null
+++ b/Documentation/devicetree/bindings/hwmon/apple,smc-hwmon.yaml
@@ -0,0 +1,86 @@
+# 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>
+
+$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
+
+properties:
+ compatible:
+ const: apple,smc-hwmon
+
+patternProperties:
+ "^current-[A-Za-z0-9]{4}$":
+ $ref: "#/$defs/sensor"
+ unevaluatedProperties: false
+
+ "^fan-[A-Za-z0-9]{4}$":
+ $ref: "#/$defs/sensor"
+ unevaluatedProperties: false
+
+ properties:
+ 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
+
+
+ "^power-[A-Za-z0-9]{4}$":
+ $ref: "#/$defs/sensor"
+ unevaluatedProperties: false
+
+ "^temperature-[A-Za-z0-9]{4}$":
+ $ref: "#/$defs/sensor"
+ unevaluatedProperties: false
+
+ "^voltage-[A-Za-z0-9]{4}$":
+ $ref: "#/$defs/sensor"
+ unevaluatedProperties: false
+
+additionalProperties: false
diff --git a/Documentation/devicetree/bindings/mfd/apple,smc.yaml b/Documentation/devicetree/bindings/mfd/apple,smc.yaml
index 0410e712c900..34ce048619f5 100644
--- a/Documentation/devicetree/bindings/mfd/apple,smc.yaml
+++ b/Documentation/devicetree/bindings/mfd/apple,smc.yaml
@@ -49,6 +49,9 @@ properties:
rtc:
$ref: /schemas/rtc/apple,smc-rtc.yaml
+ hwmon:
+ $ref: /schemas/hwmon/apple,smc-hwmon.yaml
+
additionalProperties: false
required:
@@ -89,5 +92,38 @@ examples:
nvmem-cells = <&rtc_offset>;
nvmem-cell-names = "rtc_offset";
};
+
+ hwmon {
+ compatible = "apple,smc-hwmon";
+
+ current-ID0R {
+ apple,key-id = "ID0R";
+ label = "AC Input Current";
+ };
+
+ 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-PSTR {
+ apple,key-id = "PSTR";
+ label = "Total System Power";
+ };
+
+ temperature-TW0P {
+ apple,key-id = "TW0P";
+ label = "WiFi/BT Module Temperature";
+ };
+
+ voltage-VD0R {
+ apple,key-id = "VD0R";
+ label = "AC Input Voltage";
+ };
+ };
};
};
diff --git a/MAINTAINERS b/MAINTAINERS
index 5b11839cba9d..5f160eb6762e 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2458,6 +2458,7 @@ F: Documentation/devicetree/bindings/cpufreq/apple,cluster-cpufreq.yaml
F: Documentation/devicetree/bindings/dma/apple,admac.yaml
F: Documentation/devicetree/bindings/gpio/apple,smc-gpio.yaml
F: Documentation/devicetree/bindings/gpu/apple,agx.yaml
+F: Documentation/devicetree/bindings/hwmon/apple,smc-hwmon.yaml
F: Documentation/devicetree/bindings/i2c/apple,i2c.yaml
F: Documentation/devicetree/bindings/input/touchscreen/apple,z2-multitouch.yaml
F: Documentation/devicetree/bindings/interrupt-controller/apple,*
--
2.52.0On Mon, 15 Dec 2025 19:37:45 +1000, James Calligeros wrote: > 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. > > Reviewed-by: Neal Gompa <neal@gompa.dev> > Reviewed-by: Rob Herring (Arm) <robh@kernel.org> > Signed-off-by: James Calligeros <jcalligeros99@gmail.com> > --- > .../bindings/hwmon/apple,smc-hwmon.yaml | 86 +++++++++++++++++++++++++ > .../bindings/mfd/apple,smc.yaml | 36 +++++++++++ > MAINTAINERS | 1 + > 3 files changed, 123 insertions(+) > My bot found errors running 'make dt_binding_check' on your patch: yamllint warnings/errors: ./Documentation/devicetree/bindings/hwmon/apple,smc-hwmon.yaml:73:1: [warning] too many blank lines (2 > 1) (empty-lines) dtschema/dtc warnings/errors: doc reference errors (make refcheckdocs): See https://patchwork.kernel.org/project/devicetree/patch/20251215-macsmc-subdevs-v6-1-0518cb5f28ae@gmail.com The base for the series is generally the latest rc1. A different dependency should be noted in *this* patch. If you already ran 'make dt_binding_check' and didn't see the above error(s), then make sure 'yamllint' is installed and dt-schema is up to date: pip3 install dtschema --upgrade Please check and re-submit after running the above command yourself. Note that DT_SCHEMA_FILES can be set to your schema file to speed up checking your schema. However, it must be unset to test all examples with your schema.
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