linux-kernel - Re: [PATCH 2/9] dt-bindings: iio: dac: adi-axi-adc: Add ad7606 variant

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Message-ID: <49bc9ec4-f252-4903-b5be-1d35ee8d48be@baylibre.com>
Date: Thu, 21 Nov 2024 10:57:44 -0600
From: David Lechner <dlechner@...libre.com>
To: Guillaume Stols <gstols@...libre.com>,
 Lars-Peter Clausen <lars@...afoo.de>,
 Michael Hennerich <Michael.Hennerich@...log.com>,
 Jonathan Cameron <jic23@...nel.org>, Nuno Sa <nuno.sa@...log.com>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>
Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org, jstephan@...libre.com, aardelean@...libre.com,
 adureghello@...libre.com
Subject: Re: [PATCH 2/9] dt-bindings: iio: dac: adi-axi-adc: Add ad7606
 variant

On 11/21/24 4:18 AM, Guillaume Stols wrote:
> A new compatible is added to reflect the specialized version of the HDL
> that is not covered by the IIO backend paradigm: We use the parallel

It still is being used as an IIO backend, so I would leave out the
phrase "that is not covered by the IIO backend paradigm".

> interface to write the ADC's registers, and accessing this interface
> requires to use ADI_AXI_REG_CONFIG_RD,ADI_AXI_REG_CONFIG_WR and
> ADI_AXI_REG_CONFIG_CTRL in a custom fashion.
> 
> Signed-off-by: Guillaume Stols <gstols@...libre.com>
> ---
>  Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml b/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
> index e1f450b80db2..43bc0440c678 100644
> --- a/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
> +++ b/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
> @@ -17,13 +17,20 @@ description: |
>    interface for the actual ADC, while this IP core will interface
>    to the data-lines of the ADC and handle the streaming of data into
>    memory via DMA.
> +  In some cases, the AXI ADC interface is used to perform specialized
> +  operation to a particular ADC, e.g access the physical bus through
> +  some special register to write ADC registers.
> +  In this case, a different compatible is used, and the driver behaves

Quick, delete the word "driver" before Krzysztof sees it. :-p

Joking aside, the devicetree only describes how things are wired up,
it doesn't care how the driver uses the information. So we avoid
mentioning anything about drivers in the bindings.

> +  slightly differently according to the special needs.
>  
>    https://wiki.analog.com/resources/fpga/docs/axi_adc_ip
> +  http://analogdevicesinc.github.io/hdl/library/axi_ad7606x/index.html
>  
>  properties:
>    compatible:
>      enum:
>        - adi,axi-adc-10.0.a
> +      - adi,axi-ad7606x
>  
>    reg:
>      maxItems: 1
> 

Since this new compatible also provides a bus in addition to the io-backend,
I think we need some additional bindings to describe the child nodes for the
ADC devices attached to the bus.

I don't think there are any generic parallel-controller bindings like there
are for SPI controllers, so we can't $ref: /schemas/spi/spi-controller.yaml#
like we did for the similar case of adi,axi-ad3552r recently.

But maybe something like this:

properties:
  ...

  "#address-cells":
    const: 1

  "#size-cells":
    const: 0

patternProperties:
  "^adc@[0-9a-f]+$":
    type: object
    additionalProperties: true

    properties:
      reg:
        maxItems: 1

    required:
      - compatible
      - reg