Re: [PATCH 2/8] dt-bindings: hwmon: add Apple System Management Controller hwmon schema
From: Rob Herring <robh@kernel.org>
Date: 2025-08-19 20:15:38
Also in:
asahi, linux-devicetree, linux-hwmon, linux-input, linux-rtc, lkml
On Tue, Aug 19, 2025 at 09:47:54PM +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.
I'm confused because you say this, but then the .dtsi files are common.
quoted hunk ↗ jump to hunk
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:
I don't see any need to group these and I would remove the intermediate node. We have an iterator to iterate over a matching node name prefix if that was the reasoning.
+ description: SMC current sense endpoints + type: object + additionalProperties: false
blank line
+ patternProperties:
+ "^current-[A-Za-z0-9]{4}":Missing a '$' anchor on the end.
+ type: object + additionalProperties: false
blank line.
+ required: + - apple,key-id
'required' goes after 'properties'. blank lines in between.
+ 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.blank line
+ label: + $ref: /schemas/types.yaml#/definitions/string
Already has a type, don't need to re-define it.
+ description: Human-readable name for the sensor
Instead of duplicating these properties, You can do it once under a '$defs' key and then reference it here.
+ + 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
blank line. And so on...
+ 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 matchtypo
+ the node's suffix, but doesn't have to.
Why can't we require that they match? (Other than we can't express that in schema?)
+ apple,fan-minimum:
+ $ref: /schemas/types.yaml#/definitions/string
+ pattern: "^[A-Za-z0-9]{4}"
+ description: The minimum speed the current fan can run atThis is not the speed, but the identifier key to retrieve the min speed, right? That's not clear. It's a bit odd that everything is a key id, but one property has that in the name and the others don't. I don't have any better suggestion though...
+ 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 sensorSurely more than apple,key-id is required? How would it be useful with only that? You can know how many fans you have, but have no info or control over them? Rob