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From:   Doug Anderson <dianders@chromium.org>
Date:   Fri, 29 Apr 2022 09:31:05 -0700
Message-ID: <CAD=FV=Vtnj+8FYdBSvsud9fGEbo7N1HSjXA3rH3f8FMJsuVR1A@mail.gmail.com>
Subject: Re: [PATCH 1/2] dt-bindings: google,cros-ec-keyb: Introduce switches
 only compatible
To:     Stephen Boyd <swboyd@chromium.org>
Cc:     Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>, patches@lists.linux.dev,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>, Benson Leung <bleung@chromium.org>,
        Guenter Roeck <groeck@chromium.org>,
        Hsin-Yi Wang <hsinyi@chromium.org>,
        "Joseph S. Barrera III" <joebar@chromium.org>
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Precedence: bulk

Hi,

On Wed, Apr 27, 2022 at 1:30 PM Stephen Boyd <swboyd@chromium.org> wrote:
>
> If the device is a detachable, this device won't have a matrix keyboard
> but it may have some button switches, e.g. volume buttons and power
> buttons. Let's add a more specific compatible for this type of device
> that indicates to the OS that there are only switches and no matrix
> keyboard present.
>
> Cc: Krzysztof Kozlowski <krzk@kernel.org>
> Cc: Rob Herring <robh+dt@kernel.org>
> Cc: <devicetree@vger.kernel.org>
> Cc: Benson Leung <bleung@chromium.org>
> Cc: Guenter Roeck <groeck@chromium.org>
> Cc: Douglas Anderson <dianders@chromium.org>
> Cc: Hsin-Yi Wang <hsinyi@chromium.org>
> Cc: "Joseph S. Barrera III" <joebar@chromium.org>
> Signed-off-by: Stephen Boyd <swboyd@chromium.org>
> ---
>  .../bindings/input/google,cros-ec-keyb.yaml          | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/input/google,cros-ec-keyb.yaml b/Documentation/devicetree/bindings/input/google,cros-ec-keyb.yaml
> index e8f137abb03c..edc1194d558d 100644
> --- a/Documentation/devicetree/bindings/input/google,cros-ec-keyb.yaml
> +++ b/Documentation/devicetree/bindings/input/google,cros-ec-keyb.yaml
> @@ -15,14 +15,20 @@ description: |
>    Google's ChromeOS EC Keyboard is a simple matrix keyboard
>    implemented on a separate EC (Embedded Controller) device. It provides
>    a message for reading key scans from the EC. These are then converted
> -  into keycodes for processing by the kernel.
> +  into keycodes for processing by the kernel. This device also supports
> +  switches/buttons like power and volume buttons.
>
>  allOf:
>    - $ref: "/schemas/input/matrix-keymap.yaml#"
>
>  properties:
>    compatible:
> -    const: google,cros-ec-keyb
> +    oneOf:
> +      - items:
> +          - const: google,cros-ec-keyb-switches
> +          - const: google,cros-ec-keyb
> +      - items:
> +          - const: google,cros-ec-keyb

nit: if I come back and read this binding later I'm not sure it would
be obvious which compatible I should pick. Can we give any description
here that indicates that the first choice is for devices that _only_
have buttons and switches (the google,cros-ec-keyb is just for
backward compatibility) and the second choice is for devices that have
a physical keyboard and _also_ possibly some buttons/switches?

I could also imagine people in the future being confused about whether
it's allowed to specify matrix properties even for devices that don't
have a matrix keyboard. It might be worth noting that it's allowed (to
support old drivers that might still be matching against the
google,cros-ec-keyb compatible) but not required.


>    google,needs-ghost-filter:
>      description:
> @@ -50,7 +56,7 @@ examples:
>    - |
>      #include <dt-bindings/input/input.h>
>      cros-ec-keyb {
> -        compatible = "google,cros-ec-keyb";
> +        compatible = "google,cros-ec-keyb-switches", "google,cros-ec-keyb";

Feels like we should create a second example?