Re: [PATCH v7 3/4] dt-bindings: iio: adc: ad4080: add AD4880 support

["Nuno Sá" <noname.nuno@gmail.com>]

On Sun, 2026-03-22 at 15:33 +0000, Miclaus, Antoniu wrote:
> > -----Original Message-----
> > From: Jonathan Cameron <jic23@kernel.org>
> > Sent: Saturday, March 21, 2026 2:08 PM
> > To: Miclaus, Antoniu <Antoniu.Miclaus@analog.com>
> > Cc: Lars-Peter Clausen <lars@metafoo.de>; Hennerich, Michael
> > <Michael.Hennerich@analog.com>; David Lechner <dlechner@baylibre.com>;
> > Sa, Nuno <Nuno.Sa@analog.com>; Rob Herring <robh@kernel.org>; Krzysztof
> > Kozlowski <krzk+dt@kernel.org>; Conor Dooley <conor+dt@kernel.org>;
> > Olivier Moysan <olivier.moysan@foss.st.com>; linux-iio@vger.kernel.org;
> > devicetree@vger.kernel.org; linux-kernel@vger.kernel.org
> > Subject: Re: [PATCH v7 3/4] dt-bindings: iio: adc: ad4080: add AD4880
> > support
> > 
> > [External]
> > 
> > On Sat, 21 Mar 2026 12:01:53 +0200
> > Antoniu Miclaus <antoniu.miclaus@analog.com> wrote:
> > 
> > > Add support for the AD4880, a dual-channel 20-bit 40MSPS SAR ADC
> > > with integrated fully differential amplifiers (FDA).
> > > 
> > > The AD4880 has two independent ADC channels, each with its own SPI
> > > configuration interface. This requires:
> > > - Two entries in reg property for primary and secondary channel
> > >   chip selects
> > > - Two io-backends entries for the two data channels
> > From the v6 discussion.  I'd just like to know a little more on this.
> > Are they really separate backends?
> > 
> Yes, they are separate backends. The FPGA reference design
> instantiates two independent axi_ad408x IP cores
> The AD4880 is essentially two AD4080 dies in one package.
> 
> The two data streams are merged by a util_cpack2 channel
> packer before reaching a single DMA:
> 
>     axi_ad408x (ch A) --
>                          --> util_cpack2 --> single DMA
>     axi_ad408x (ch B) --/
> 
> Each backend needs independent LVDS alignment and lane
> configuration, so a single-backend-with-channel-parameter
> model wouldn't fit here.
> 
> https://github.com/analogdevicesinc/hdl/blob/main/projects/ad4880_fmc_evb/common/ad4880_fmc_evb_bd.tcl


I was not really involved in this part but this whole discussion got me curious about why are
we going with the interleaved approach? Typically when each path has it's own serial interface, we
also have a separate DMA channel.

- Nuno Sá

> 
> > Given discussion about interleaved data, I was kind of assuming they
> > were different front end interfaces to a single backend IP.
> > 
> > The freedom this binding is giving is for those two backends to be
> > completely unrelated. I'm not sure if we want that.
> > 
> > Jonathan
> > 
> > 
> > > 
> > > Reviewed-by: David Lechner <dlechner@baylibre.com>
> > > Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
> > > ---
> > > Changes in v7:
> > >   - No changes
> > > 
> > >  .../bindings/iio/adc/adi,ad4080.yaml          | 53 ++++++++++++++++++-
> > >  1 file changed, 51 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ad4080.yaml
> > b/Documentation/devicetree/bindings/iio/adc/adi,ad4080.yaml
> > > index ccd6a0ac1539..0cf86c6f9925 100644
> > > --- a/Documentation/devicetree/bindings/iio/adc/adi,ad4080.yaml
> > > +++ b/Documentation/devicetree/bindings/iio/adc/adi,ad4080.yaml
> > > @@ -18,7 +18,11 @@ description: |
> > >    service a wide variety of precision, wide bandwidth data acquisition
> > >    applications.
> > > 
> > > +  The AD4880 is a dual-channel variant with two independent ADC
> > channels,
> > > +  each with its own SPI configuration interface.
> > > +
> > >    https://www.analog.com/media/en/technical-documentation/data-
> > sheets/ad4080.pdf
> > > +  https://www.analog.com/media/en/technical-documentation/data-
> > sheets/ad4880.pdf
> > > 
> > >  $ref: /schemas/spi/spi-peripheral-props.yaml#
> > > 
> > > @@ -31,9 +35,15 @@ properties:
> > >        - adi,ad4084
> > >        - adi,ad4086
> > >        - adi,ad4087
> > > +      - adi,ad4880
> > > 
> > >    reg:
> > > -    maxItems: 1
> > > +    minItems: 1
> > > +    maxItems: 2
> > > +    description:
> > > +      SPI chip select(s). For single-channel devices, one chip select.
> > > +      For multi-channel devices like AD4880, two chip selects are required
> > > +      as each channel has its own SPI configuration interface.
> > > 
> > >    spi-max-frequency:
> > >      description: Configuration of the SPI bus.
> > > @@ -57,7 +67,10 @@ properties:
> > >    vrefin-supply: true
> > > 
> > >    io-backends:
> > > -    maxItems: 1
> > > +    minItems: 1
> > > +    items:
> > > +      - description: Backend for channel A (primary)
> > > +      - description: Backend for channel B (secondary)
> > > 
> > >    adi,lvds-cnv-enable:
> > >      description: Enable the LVDS signal type on the CNV pin. Default is CMOS.
> > > @@ -78,6 +91,25 @@ required:
> > >    - vdd33-supply
> > >    - vrefin-supply
> > > 
> > > +allOf:
> > > +  - if:
> > > +      properties:
> > > +        compatible:
> > > +          contains:
> > > +            const: adi,ad4880
> > > +    then:
> > > +      properties:
> > > +        reg:
> > > +          minItems: 2
> > > +        io-backends:
> > > +          minItems: 2
> > > +    else:
> > > +      properties:
> > > +        reg:
> > > +          maxItems: 1
> > > +        io-backends:
> > > +          maxItems: 1
> > > +
> > >  additionalProperties: false
> > > 
> > >  examples:
> > > @@ -98,4 +130,21 @@ examples:
> > >            io-backends = <&iio_backend>;
> > >          };
> > >      };
> > > +  - |
> > > +    spi {
> > > +        #address-cells = <1>;
> > > +        #size-cells = <0>;
> > > +
> > > +        adc@0 {
> > > +          compatible = "adi,ad4880";
> > > +          reg = <0>, <1>;
> > > +          spi-max-frequency = <10000000>;
> > > +          vdd33-supply = <&vdd33>;
> > > +          vddldo-supply = <&vddldo>;
> > > +          vrefin-supply = <&vrefin>;
> > > +          clocks = <&cnv>;
> > > +          clock-names = "cnv";
> > > +          io-backends = <&iio_backend_cha>, <&iio_backend_chb>;
> > > +        };
> > > +    };
> > >  ...