linux-kernel - Re: [PATCH 2/5] dt-bindings: iio: ad74413r: make refin-supply optional

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Date:   Sat, 12 Nov 2022 16:54:48 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Cosmin Tanislav <cosmin.tanislav@...log.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] dt-bindings: iio: ad74413r: make refin-supply
 optional

On Fri, 11 Nov 2022 15:39:18 +0100
Rasmus Villemoes <linux@...musvillemoes.dk> wrote:

> The ad74412r/ad74413r has an internal 2.5V reference output, which (by
> tying the REFOUT pin to the REFIN pin) can be used in lieu of an
> external 2.5V input reference. So stop marking refin-supply as
> required.
> 
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>

Interesting corner case.  Given we have no way of knowing if the
wiring has REFOUT connected to REFIN I see two ways we should fix this.

1) Just have any DT doing this provide a fixed regulator.
2) Have the REFOUT supported as an actual regulator - in theory it might be
   wired to other devices.  This might get a little interesting ordering
   wise as we'll want to register the regulator before we try to consume
   it in the same driver.  I'm also not 100% sure there are no other issues
   in a driver providing and consuming the same regulator.

I'm not keen to just assume lack of regulator means the chip is wired
like this.  Would be a different question if this was just setting
an internal mux to use the regulator without external loop back being
needed.

Jonathan

> ---
>  Documentation/devicetree/bindings/iio/addac/adi,ad74413r.yaml | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/Documentation/devicetree/bindings/iio/addac/adi,ad74413r.yaml b/Documentation/devicetree/bindings/iio/addac/adi,ad74413r.yaml
> index 03bb90a7f4f8..e954d5ae4f4f 100644
> --- a/Documentation/devicetree/bindings/iio/addac/adi,ad74413r.yaml
> +++ b/Documentation/devicetree/bindings/iio/addac/adi,ad74413r.yaml
> @@ -56,7 +56,6 @@ required:
>    - reg
>    - spi-max-frequency
>    - spi-cpol
> -  - refin-supply
>  
>  additionalProperties: false
>