linux-kernel - Re: [PATCH v2 1/2] dt-bindings: staging: iio: cdc: ad7746: add binding documentation for AD7746

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Message-ID: <CACKVXZDtUync4HnScJnMEj=Gh7bukUUpnPrtE0w1PPgCZOHORg@mail.gmail.com>
Date:   Thu, 22 Apr 2021 16:16:21 -0300
From:   Lucas Stankus <lucas.p.stankus@...il.com>
To:     Rob Herring <robh@...nel.org>
Cc:     lars@...afoo.de, Michael.Hennerich@...log.com, jic23@...nel.org,
        gregkh@...uxfoundation.org, linux-iio@...r.kernel.org,
        linux-staging@...ts.linux.dev,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v2 1/2] dt-bindings: staging: iio: cdc: ad7746: add
 binding documentation for AD7746

On Tue, Apr 20, 2021 at 4:37 PM Rob Herring <robh@...nel.org> wrote:
>
> On Sun, Apr 18, 2021 at 07:49:51PM -0300, Lucas Stankus wrote:
> > Add device tree binding documentation for AD7746 cdc in YAML format.
> >
> > Signed-off-by: Lucas Stankus <lucas.p.stankus@...il.com>
> > ---
> >
> > A minor note about the adi,excitation-vdd-permille property. Jonathan
> > suggested the name to be adi,excitation-vdd-milicent, but I was unsure of
> > the milicent naming. With a quick search I found out that the common way to
> > call a thousandth is 'per mille'[1], but I didn't find any use of it in the
> > kernel documentation. Any thoughts about it?
>
> Seems okay to me.
>
> > [1] https://en.wikipedia.org/wiki/Per_mille
> >
> >  .../bindings/iio/cdc/adi,ad7746.yaml          | 73 +++++++++++++++++++
> >  1 file changed, 73 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/iio/cdc/adi,ad7746.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/iio/cdc/adi,ad7746.yaml b/Documentation/devicetree/bindings/iio/cdc/adi,ad7746.yaml
> > new file mode 100644
> > index 000000000000..a2a7eee674ba
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/iio/cdc/adi,ad7746.yaml
> > @@ -0,0 +1,73 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/iio/cdc/adi,ad7746.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: AD7746 24-Bit Capacitance-to-Digital Converter with Temperature Sensor
> > +
> > +maintainers:
> > +  - Michael Hennerich <michael.hennerich@...log.com>
> > +
> > +description: |
> > +  AD7746 24-Bit Capacitance-to-Digital Converter with Temperature Sensor
> > +
> > +  Specifications about the part can be found at:
> > +  https://www.analog.com/media/en/technical-documentation/data-sheets/ad7291.pdf
> > +
> > +properties:
> > +  compatible:
> > +    enum:
> > +      - adi,ad7745
> > +      - adi,ad7746
> > +      - adi,ad7747
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  adi,excitation-vdd-permille:
> > +    description: |
> > +      Set VDD per mille to be used as the excitation voltage.
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    enum: [125, 250, 375, 500]
> > +
> > +  adi,exca-output-en:
> > +    description: Enables the EXCA pin as the excitation output.
> > +    type: boolean
> > +
> > +  adi,exca-output-invert:
> > +    description: Inverts the excitation output in the EXCA pin.
> > +    type: boolean
>
> 'invert' assumes I know what the non-inverted signal is. Sometimes that
> makes sense, but if you can define in terms of the inverse that would be
> better. For example, for a normally active low signal, name the property
> 'foo-active-high'.

Thanks for the feedback!
>From reading the data sheet I couldn't quite grasp what would be an inverted
excitation output, but I don't have a lot of experience with CDCs. Maybe someone
with more experience could help out with a better suggestion.

>
> > +
> > +  adi,excb-output-en:
> > +    description: Enables the EXCB pin as the excitation output.
> > +    type: boolean
> > +
> > +  adi,excb-output-invert:
> > +    description: Inverts the excitation output in the EXCB pin.
> > +    type: boolean
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    i2c {
> > +      #address-cells = <1>;
> > +      #size-cells = <0>;
> > +
> > +      ad7746: cdc@48 {
> > +        compatible = "adi,ad7746";
> > +        reg = <0x48>;
> > +        adi,excitation-vdd-permille = <125>;
> > +
> > +        adi,exca-output-en;
> > +        adi,exca-output-invert;
> > +        adi,excb-output-en;
> > +        adi,excb-output-invert;
> > +      };
> > +    };
> > +...
> > --
> > 2.31.1
> >