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

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Message-ID: <aVKDJhVuOz-V9tb2@google.com>
Date: Mon, 29 Dec 2025 13:33:26 +0000
From: Fabio Baltieri <fabiobaltieri@...omium.org>
To: Krzysztof Kozlowski <krzk@...nel.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 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
linux,keymap property and the driver needs to know that there's an extra
layer to interpret the codes correctly.

> >>> +      that are sent if a key is pressed while the KEY_FN is held pressed as
> >>> +      well. The function codes have to be defined in the linux,keymap property
> >>> +      with an offset of keypad,num-rows from the normal ones.
> >>> +    type: boolean
> >>> +
> >>>  dependencies:
> >>>    function-row-physmap: [ 'linux,keymap' ]
> >>>    google,needs-ghost-filter: [ 'linux,keymap' ]
> >>> @@ -132,6 +140,23 @@ examples:
> >>>              /* UP      LEFT    */
> >>>              0x070b0067 0x070c0069>;
> >>>      };
> >>> +  - |
> >>> +    /* With function keys */
> >>> +    #include <dt-bindings/input/input.h>
> >>> +    keyboard-controller {
> >>> +        compatible = "google,cros-ec-keyb";
> >>> +        keypad,num-rows = <8>;
> >>> +        keypad,num-columns = <18>;
> >>> +        google,use-fn-overlay;
> >>
> >> Difference in one property does not justify new example.
> > 
> > Sure but when the property is set then one has to specify the extra
> > codes in the linux,keymap property and this examples shows how. I'll
> > drop it if you want me to but I think there's value in it.
> 
> Examples are for verifying schema and you do not have schema enforcing
> this, thus still pointless. Add schema for that, assuming property will
> stay.

Ok got it, I'll just drop it in v3.