linux-kernel - Re: [PATCH 2/8] dt-bindings: hwmon: add Apple System Management Controller hwmon schema

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Message-ID: <4a95cbf3-b3ae-4b26-8db2-dd5cf14a4c0c@kernel.org>
Date: Thu, 21 Aug 2025 17:25:32 +0200
From: Sven Peter <sven@...nel.org>
To: James Calligeros <jcalligeros99@...il.com>, Rob Herring <robh@...nel.org>
Cc: Janne Grunau <j@...nau.net>, Alyssa Rosenzweig <alyssa@...enzweig.io>,
 Neal Gompa <neal@...pa.dev>, Lee Jones <lee@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Alexandre Belloni <alexandre.belloni@...tlin.com>,
 Jean Delvare <jdelvare@...e.com>, Guenter Roeck <linux@...ck-us.net>,
 Dmitry Torokhov <dmitry.torokhov@...il.com>, asahi@...ts.linux.dev,
 linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-rtc@...r.kernel.org,
 linux-hwmon@...r.kernel.org, linux-input@...r.kernel.org
Subject: Re: [PATCH 2/8] dt-bindings: hwmon: add Apple System Management
 Controller hwmon schema

On 20.08.25 01:22, James Calligeros wrote:
> Hi Rob,
> 
> On Wed, Aug 20, 2025 at 6:15 AM Rob Herring <robh@...nel.org> wrote:
>>

[...]

>>> +          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
>>
>> Surely 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?
> 
> The key specified in apple,key-id is the fan's current speed, which is the
> only key strictly required to enumerate the presence of a fan in the system.
> All of the other keys are optional information that are only really useful
> when implementing manual fan control, which is itself optional as the platform
> really expects the SMC firmware to have control over fan speeds at all times.


Can we at least also require the label? Then we have the SMC key and a 
human readable representation which is already useful.


Sven