linux-kernel - Re: [PATCH v6 2/2] dt-bindings: cros-ec: Add ChromeOS fingerprint binding

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Message-ID: <20220627215720.GA3004792-robh@kernel.org>
Date:   Mon, 27 Jun 2022 15:57:20 -0600
From:   Rob Herring <robh@...nel.org>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Stephen Boyd <swboyd@...omium.org>,
        Benson Leung <bleung@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>, patches@...ts.linux.dev,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, chrome-platform@...ts.linux.dev,
        Guenter Roeck <groeck@...omium.org>,
        Craig Hesling <hesling@...omium.org>,
        Tom Hughes <tomhughes@...omium.org>,
        Alexandru M Stan <amstan@...omium.org>,
        Tzung-Bi Shih <tzungbi@...nel.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Lee Jones <lee.jones@...aro.org>
Subject: Re: [PATCH v6 2/2] dt-bindings: cros-ec: Add ChromeOS fingerprint
 binding

On Tue, Jun 14, 2022 at 03:41:25PM -0700, Doug Anderson wrote:
> Hi,
> 
> On Tue, Jun 14, 2022 at 12:51 PM Stephen Boyd <swboyd@...omium.org> wrote:
> >
> > Add a binding to describe the fingerprint processor found on Chromebooks
> > with a fingerprint sensor. Previously we've been describing this with
> > the google,cros-ec-spi binding but it lacks gpio and regulator control
> > used during firmware flashing.
> >
> > Cc: Rob Herring <robh+dt@...nel.org>
> > Cc: Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
> > Cc: <devicetree@...r.kernel.org>
> > Cc: <chrome-platform@...ts.linux.dev>
> > Cc: Guenter Roeck <groeck@...omium.org>
> > Cc: Douglas Anderson <dianders@...omium.org>
> > Cc: Craig Hesling <hesling@...omium.org>
> > Cc: Tom Hughes <tomhughes@...omium.org>
> > Cc: Alexandru M Stan <amstan@...omium.org>
> > Cc: Tzung-Bi Shih <tzungbi@...nel.org>
> > Cc: Matthias Kaehlcke <mka@...omium.org>
> > Cc: Benson Leung <bleung@...omium.org>
> > Cc: Lee Jones <lee.jones@...aro.org>
> > Signed-off-by: Stephen Boyd <swboyd@...omium.org>
> > ---
> >  .../bindings/chrome/google,cros-ec-fp.yaml    | 97 +++++++++++++++++++
> >  .../bindings/mfd/google,cros-ec.yaml          |  9 ++
> >  2 files changed, 106 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/chrome/google,cros-ec-fp.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/chrome/google,cros-ec-fp.yaml b/Documentation/devicetree/bindings/chrome/google,cros-ec-fp.yaml
> > new file mode 100644
> > index 000000000000..48c02bd4585c
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/chrome/google,cros-ec-fp.yaml
> > @@ -0,0 +1,97 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/chrome/google,cros-ec-fp.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: ChromeOS Embedded Fingerprint Controller
> > +
> > +description:
> > +  Google's ChromeOS embedded fingerprint controller is a device which
> > +  implements fingerprint functionality such as unlocking a Chromebook
> > +  without typing a password.
> > +
> > +maintainers:
> > +  - Tom Hughes <tomhughes@...omium.org>
> > +
> > +select:
> > +  properties:
> > +    compatible:
> > +      contains:
> > +        const: google,cros-ec-spi
> > +  required:
> > +    - compatible
> > +    - boot0-gpios
> 
> I've never personally used "select" before and I'm not sure where it's
> documented. 

Documentation/devicetree/bindings/writing-schema.rst

> Without knowing anything, it seems weird to me that in
> this file we're matching against a compatible that's not
> google,cros-ec-fp. Randomly grabbing some other example that's similar
> (panel-lvds.yaml) looks more like what I would have expected. AKA in
> this file:
> 
> select:
>   properties:
>     compatible:
>       contains:
>         const: google,cros-ec-fp
>   required:
>     - compatible
> 
> ...and then in the other file:
> 
> select:
>   properties:
>     compatible:
>       contains:
>         const: google,cros-ec-spi

What about i2c and rpmsg variants?

>   not:
>     properties:
>       compatible:
>         contains:
>           const: google,cros-ec-fp
>   required:
>     - compatible

That is what is needed assuming the binding stands as-is. Otherwise, 
boot0-gpios erroneously present or missing will give unexpected results.

If we were starting from scratch, I would say you should just drop 
'google,cros-ec-spi' from this binding. But I guess you want to preserve 
compatibility here. In that case, I think all this should be added to 
the existing doc with an if/then schema for conditional parts. That also 
avoids defining the common properties twice or moving them to a common, 
shared schema.

Rob