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

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Message-ID: <8b2c672a-f260-fe19-5baf-adf6ce6fabf2@metafoo.de>
Date:   Thu, 22 Apr 2021 22:56:38 +0200
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Lucas Stankus <lucas.p.stankus@...il.com>,
        Rob Herring <robh@...nel.org>
Cc:     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 4/22/21 9:16 PM, Lucas Stankus wrote:
> 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.

This is the only thing I could find 
https://www.analog.com/media/en/technical-documentation/application-notes/AN-1585.pdf.

The datasheet also says that only at most one of them should be 
inverted. So maybe only a single property which selects which of the two 
is inverted.