linux-kernel - Re: [PATCH v2 5/6] dt-bindings: iio: adc: adi,ad7380: add spi-buses property

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Message-ID: <CAL_Jsq+ZZE0g424jE75xeCt2KY1ThPLqmbmOs0o_ddaJ8fOf3w@mail.gmail.com>
Date: Wed, 19 Nov 2025 07:18:05 -0600
From: Rob Herring <robh@...nel.org>
To: David Lechner <dlechner@...libre.com>
Cc: Mark Brown <broonie@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, Marcelo Schmitt <marcelo.schmitt@...log.com>, 
	Michael Hennerich <michael.hennerich@...log.com>, Nuno Sá <nuno.sa@...log.com>, 
	Jonathan Cameron <jic23@...nel.org>, Andy Shevchenko <andy@...nel.org>, 
	Sean Anderson <sean.anderson@...ux.dev>, linux-spi@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-iio@...r.kernel.org
Subject: Re: [PATCH v2 5/6] dt-bindings: iio: adc: adi,ad7380: add spi-buses property

On Tue, Nov 18, 2025 at 11:46 AM David Lechner <dlechner@...libre.com> wrote:
>
> On 11/18/25 9:59 AM, Rob Herring wrote:
> > On Fri, Nov 07, 2025 at 02:52:51PM -0600, David Lechner wrote:
> >> Add spi-buses property to describe how many SDO lines are wired up on
> >> the ADC. These chips are simultaneous sampling ADCs and have one SDO
> >> line per channel, either 2 or 4 total depending on the part number.
> >>
> >> Signed-off-by: David Lechner <dlechner@...libre.com>
> >> ---
> >>  .../devicetree/bindings/iio/adc/adi,ad7380.yaml    | 22 ++++++++++++++++++++++
> >>  1 file changed, 22 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ad7380.yaml b/Documentation/devicetree/bindings/iio/adc/adi,ad7380.yaml
> >> index b91bfb16ed6bc6c605880f81050250d1ed9c307a..9ef46cdb047d45d088e0fbc345f58c5b09083385 100644
> >> --- a/Documentation/devicetree/bindings/iio/adc/adi,ad7380.yaml
> >> +++ b/Documentation/devicetree/bindings/iio/adc/adi,ad7380.yaml
> >> @@ -62,6 +62,10 @@ properties:
> >>    spi-cpol: true
> >>    spi-cpha: true
> >>
> >> +  spi-data-buses:
> >> +    minItems: 1
> >> +    maxItems: 4
> >> +
> >
> > As the property is not required, what's the default?
>
> spi-perepheral-props.yaml defines:
>
>         default: [0]
>
> Do I need to repeat that here?

No. So that means you only use one channel and the others are not connected?

>
> >
> >>    vcc-supply:
> >>      description: A 3V to 3.6V supply that powers the chip.
> >>
> >> @@ -245,6 +249,22 @@ allOf:
> >>        patternProperties:
> >>          "^channel@[0-3]$": false
> >>
> >> +  # 2-channel chip can only have up to 2 buses
> >> +  - if:
> >> +      properties:
> >> +        compatible:
> >> +          enum:
> >> +            - adi,ad7380
> >> +            - adi,ad7381
> >> +            - adi,ad7386
> >> +            - adi,ad7387
> >> +            - adi,ad7388
> >> +            - adi,ad7389
> >> +    then:
> >> +      properties:
> >> +        spi-data-buses:
> >> +          maxItems: 2
> >> +
> >>  examples:
> >>    - |
> >>      #include <dt-bindings/interrupt-controller/irq.h>
> >> @@ -260,6 +280,7 @@ examples:
> >>              spi-cpol;
> >>              spi-cpha;
> >>              spi-max-frequency = <80000000>;
> >> +            spi-data-buses = <0>, <1>;
> >>
> >>              interrupts = <27 IRQ_TYPE_EDGE_FALLING>;
> >>              interrupt-parent = <&gpio0>;
> >> @@ -284,6 +305,7 @@ examples:
> >>              spi-cpol;
> >>              spi-cpha;
> >>              spi-max-frequency = <80000000>;
> >> +            spi-data-buses = <0>, <1>, <2>, <3>;
> >
> > An example that doesn't look like a 1 to 1 mapping would be better.
> > Otherwise, it still looks to me like you could just define the bus
> > width.
>
> I'm not sure we could do that on this chip since it doesn't have
> the possibility of more than one line per channel.

That's a property of the SPI controller though, right?

If the above controller had 4 lines per channel/serializer, then you could have:

spi-data-buses = <0>, <4>, <8>, <12>;

Rob