linux-kernel - Re: [PATCH v2 2/2] dt-bindings: google,cros-ec-keyb: add use-fn-overlay prop

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Message-ID: <e0f7c2f1-c876-4e19-a836-2b1629cdabf7@kernel.org>
Date: Tue, 30 Dec 2025 08:26:56 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Fabio Baltieri <fabiobaltieri@...omium.org>
Cc: Dmitry Torokhov <dmitry.torokhov@...il.com>, Rob Herring
 <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Benson Leung <bleung@...omium.org>,
 Guenter Roeck <groeck@...omium.org>, Tzung-Bi Shih <tzungbi@...nel.org>,
 Simon Glass <sjg@...omium.org>, linux-input@...r.kernel.org,
 devicetree@...r.kernel.org, chrome-platform@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] dt-bindings: google,cros-ec-keyb: add
 use-fn-overlay prop

On 29/12/2025 16:39, Fabio Baltieri wrote:
> On Mon, Dec 29, 2025 at 03:59:44PM +0100, Krzysztof Kozlowski wrote:
>> On 29/12/2025 14:33, Fabio Baltieri wrote:
>>> On Mon, Dec 29, 2025 at 01:49:05PM +0100, Krzysztof Kozlowski wrote:
>>>> On 27/12/2025 16:48, Fabio Baltieri wrote:
>>>>> On Sat, Dec 27, 2025 at 01:44:26PM +0100, Krzysztof Kozlowski wrote:
>>>>>>> diff --git a/Documentation/devicetree/bindings/input/google,cros-ec-keyb.yaml b/Documentation/devicetree/bindings/input/google,cros-ec-keyb.yaml
>>>>>>> index fefaaf46a240..437575cdf352 100644
>>>>>>> --- a/Documentation/devicetree/bindings/input/google,cros-ec-keyb.yaml
>>>>>>> +++ b/Documentation/devicetree/bindings/input/google,cros-ec-keyb.yaml
>>>>>>> @@ -44,6 +44,14 @@ properties:
>>>>>>>        where the lower 16 bits are reserved. This property is specified only
>>>>>>>        when the keyboard has a custom design for the top row keys.
>>>>>>>  
>>>>>>> +  google,use-fn-overlay:
>>>>>>> +    description: |
>>>>>>> +      Use a function key overlay. This allows defining an extra set of codes
>>>>>>
>>>>>> What is a function key overlay? Overlays are DT term and therefore are
>>>>>> not suitable for bindings.
>>>>>
>>>>> Ok, guess I can rename it to `use-fn-key` or `use-fn-layer`, open to
>>>>> suggestions really.
>>>>
>>>> Use as Linux should use? Then it's software, so not suitable for DT.
>>>
>>> Sorry I'm not sure how I understand the comment, this describes how the
>>> driver handles a keyboard with Fn keys, the codes are defined in the DT
>>
>> Exactly. The purpose of DT is not to describe how driver should handle
>> anything.
>>
>> See also DTS101 from this year's ELCE.
> 
> Sure so I guess this falls into the "describe the hardware feature"
> category, so is the suggestion to rename it to something like
> "has-fn-key"? That would be the hardware feature.


Maybe, but then I would follow up with - what about "alt", "ctrl",
"shift" and "fn" keys? And what about combinations alt+ctrl, alt+shift?
And also caps-lock? And why exactly this has to be even specified if
matrix map already has the FN key?

Best regards,
Krzysztof