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SubjectRe: [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@chromium.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@kernel.org>
> > Cc: Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>
> > Cc: <devicetree@vger.kernel.org>
> > Cc: <chrome-platform@lists.linux.dev>
> > Cc: Guenter Roeck <groeck@chromium.org>
> > Cc: Douglas Anderson <dianders@chromium.org>
> > Cc: Craig Hesling <hesling@chromium.org>
> > Cc: Tom Hughes <tomhughes@chromium.org>
> > Cc: Alexandru M Stan <amstan@chromium.org>
> > Cc: Tzung-Bi Shih <tzungbi@kernel.org>
> > Cc: Matthias Kaehlcke <mka@chromium.org>
> > Cc: Benson Leung <bleung@chromium.org>
> > Cc: Lee Jones <lee.jones@linaro.org>
> > Signed-off-by: Stephen Boyd <swboyd@chromium.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@chromium.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

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