linux-kernel - Re: [PATCH 1/6] dt-bindings: adc: ad7173: add support for ad411x

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Date: Mon, 1 Apr 2024 16:16:40 -0500
From: David Lechner <dlechner@...libre.com>
To: dumitru.ceclan@...log.com
Cc: Lars-Peter Clausen <lars@...afoo.de>, Michael Hennerich <Michael.Hennerich@...log.com>, 
	Jonathan Cameron <jic23@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	linux-iio@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Dumitru Ceclan <mitrutzceclan@...il.com>
Subject: Re: [PATCH 1/6] dt-bindings: adc: ad7173: add support for ad411x

On Mon, Apr 1, 2024 at 2:37 PM David Lechner <dlechner@...libre.com> wrote:
>
> On Mon, Apr 1, 2024 at 10:10 AM Dumitru Ceclan via B4 Relay
> <devnull+dumitru.ceclan.analog.com@...nel.org> wrote:
> >
> > From: Dumitru Ceclan <dumitru.ceclan@...log.com>
> >
> > Add support for: AD4111, AD4112, AD4114, AD4115, AD4116.
> >
> > AD411x family ADCs support a VCOM pin, dedicated for single-ended usage.
> > AD4111/AD4112 support current channels, usage is implemented by
> >  specifying channel reg values bigger than 15.
> >
> > Signed-off-by: Dumitru Ceclan <dumitru.ceclan@...log.com>
> > ---

..

> > @@ -125,10 +141,19 @@ patternProperties:
> >
> >      properties:
> >        reg:
> > +        description:
> > +          Reg values 16-19 are only permitted for ad4111/ad4112 current channels.
> >          minimum: 0
> > -        maximum: 15
> > +        maximum: 19
>
> This looks wrong. Isn't reg describing the number of logical channels
> (# of channel config registers)?
>
> After reviewing the driver, I see that > 16 is used as a way of
> flagging current inputs, but still seems like the wrong way to do it.
> See suggestion below.
>
> >
> >        diff-channels:
> > +        description:
> > +          For using current channels specify only the positive channel.
> > +            (IIN2+, IIN2−) -> diff-channels = <2 0>
>
> I find this a bit confusing since 2 is already VIN2 and 0 is already
> VIN0. I think it would make more sense to assign unique channel
> numbers individually to the negative and positive current inputs.
> Also, I think it makes sense to use the same numbers that the
> registers in the datasheet use (8 - 11 for negative and 12 to 15 for
> positive).
>
> So: (IIN2+, IIN2−) -> diff-channels = <13 10>

Thinking about this a bit more...

Since the current inputs have dedicated pins and aren't mix-and-match
with multiple valid wiring configurations like the voltage inputs, do
we even need to describe them in the devicetree?

In the driver, the current channels would just be hard-coded like the
temperature channel since there isn't any application-specific
variation.