Re: [PATCH v3 04/10] dt-bindings: iio: dac: ad3552r: add io-backend support

[Angelo Dureghello]

Hi Krzysztof,

On 22/09/24 23:02, Krzysztof Kozlowski wrote:
> On Thu, Sep 19, 2024 at 11:20:00AM +0200, Angelo Dureghello wrote:
> > From: Angelo Dureghello <adureghello@xxxxxxxxxxxx>
> >
> > There is a version AXI DAC IP block (for FPGAs) that provides
> > a physical bus for AD3552R and similar chips, and acts as
> > an SPI controller.
> >
> > For this case, the binding is modified to include some
> > additional properties.
> >
> > Signed-off-by: Angelo Dureghello <adureghello@xxxxxxxxxxxx>
> > ---
> >   .../devicetree/bindings/iio/dac/adi,ad3552r.yaml   | 42 ++++++++++++++++++++++
> >   1 file changed, 42 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/iio/dac/adi,ad3552r.yaml b/Documentation/devicetree/bindings/iio/dac/adi,ad3552r.yaml
> > index 41fe00034742..aca4a41c2633 100644
> > --- a/Documentation/devicetree/bindings/iio/dac/adi,ad3552r.yaml
> > +++ b/Documentation/devicetree/bindings/iio/dac/adi,ad3552r.yaml
> > @@ -60,6 +60,18 @@ properties:
> >       $ref: /schemas/types.yaml#/definitions/uint32
> >       enum: [0, 1, 2, 3]
> >   
> > +  io-backends:
> > +    description: The iio backend reference.
> > +      An example backend can be found at
> > +        https://analogdevicesinc.github.io/hdl/library/axi_ad3552r/index.html
> > +    maxItems: 1
> > +
> > +  adi,synchronous-mode:
> > +    description: Enable waiting for external synchronization signal.
> > +      Some AXI IP configuration can implement a dual-IP layout, with internal
> > +      wirings for streaming synchronization.
> > +    type: boolean
> > +
> >     '#address-cells':
> >       const: 1
> >   
> > @@ -128,6 +140,7 @@ patternProperties:
> >             - custom-output-range-config
> >   
> >   allOf:
> > +  - $ref: /schemas/spi/spi-peripheral-props.yaml#
> >     - if:
> >         properties:
> >           compatible:
> > @@ -238,4 +251,33 @@ examples:
> >               };
> >           };
> >       };
> > +
> > +  - |
> > +    axi_dac: spi@44a70000 {
> > +        compatible = "adi,axi-ad3552r";
> That is either redundant or entire example should go to the parent node,
> if this device is fixed child of complex device (IOW, adi,ad3552r cannot
> be used outside of adi,axi-ad3552r).

ad3552r can still be used by a generic "classic" spi
controller (SCLK/CS/MISO) but at a slower samplerate, fpga
controller only (axi-ad3552r) can reach 33MUPS.

> > +        reg = <0x44a70000 0x1000>;
> > +        dmas = <&dac_tx_dma 0>;
> > +        dma-names = "tx";
> > +        #io-backend-cells = <0>;
> > +        clocks = <&ref_clk>;
> > +
> > +        #address-cells = <1>;
> > +        #size-cells = <0>;
> > +
> > +        dac@0 {
> > +            compatible = "adi,ad3552r";
> > +            reg = <0>;
> > +            reset-gpios = <&gpio0 92 0>;
> Use standard defines for GPIO flags.

fixed, thanks

> > +            io-backends = <&axi_dac>;
> Why do you need to point to the parent? How much coupled are these
> devices? Child pointing to parent is not usually expected, because
> that's obvious.


"io-backends" is actually the way to refer to the backend module,
(used already for i.e. ad9739a),
it is needed because the backend is not only acting as spi-controller,
but is also providing some APIs for synchronization and bus setup support.

> Best regards,
> Krzysztof
Thanks,
Regards,
Angelo