linux-kernel - Re: [PATCH v3 02/10] dt-bindings: iio: dac: axi-dac: add ad3552r axi variant

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Message-ID: <20240929114606.7500ba7e@jic23-huawei>
Date: Sun, 29 Sep 2024 11:46:06 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Angelo Dureghello <adureghello@...libre.com>
Cc: Lars-Peter Clausen <lars@...afoo.de>, Michael Hennerich
 <Michael.Hennerich@...log.com>, Nuno Sa <nuno.sa@...log.com>, Rob Herring
 <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Olivier Moysan <olivier.moysan@...s.st.com>,
 linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org, dlechner@...libre.com, Mark Brown
 <broonie@...nel.org>, linux-spi@...r.kernel.org
Subject: Re: [PATCH v3 02/10] dt-bindings: iio: dac: axi-dac: add ad3552r
 axi variant

On Thu, 19 Sep 2024 11:19:58 +0200
Angelo Dureghello <adureghello@...libre.com> wrote:

> From: Angelo Dureghello <adureghello@...libre.com>
> 
> Add a new compatible and related bindigns for the fpga-based
> "ad3552r" AXI IP core, a variant of the generic AXI DAC IP.
> 
> The AXI "ad3552r" IP is a very similar HDL (fpga) variant of the
> generic AXI "DAC" IP, intended to control ad3552r and similar chips,
> mainly to reach high speed transfer rates using an additional QSPI

I'd drop the word additional as I assume it is an 'either/or' situation
for the interfaces.

Do we have other devices using this same IP?  I.e. does it make
sense to provide a more generic compatible as a fallback for this one
so that other devices would work without the need for explicit support?


I'd also ideally like a view point from Mark Brown as SPI maintainer
on how we should deal with this highly specialized spi controller.
Is he happy with us using an SPI like binding but not figuring out how
to fit this engine into the SPI subsystem.

Please +CC Mark and the spi list (done here) on future versions + provide
a clear description of what is going on for them.

Maybe with the binding fixed as spi compliant, we can figure out the
if we eventually want to treat this as an SPI controller from the
kernel driver point of view even if we initially do something 'special'.

Jonathan


> DDR interface.
> 
> The ad3552r device is defined as a child of the AXI DAC, that in
> this case is acting as an SPI controller.
> 
> Signed-off-by: Angelo Dureghello <adureghello@...libre.com>
> ---
>  .../devicetree/bindings/iio/dac/adi,axi-dac.yaml   | 40 ++++++++++++++++++++--
>  1 file changed, 37 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/iio/dac/adi,axi-dac.yaml b/Documentation/devicetree/bindings/iio/dac/adi,axi-dac.yaml
> index a55e9bfc66d7..6cf0c2cb84e7 100644
> --- a/Documentation/devicetree/bindings/iio/dac/adi,axi-dac.yaml
> +++ b/Documentation/devicetree/bindings/iio/dac/adi,axi-dac.yaml
> @@ -19,11 +19,13 @@ description: |
>    memory via DMA into the DAC.
>  
>    https://wiki.analog.com/resources/fpga/docs/axi_dac_ip
> +  https://analogdevicesinc.github.io/hdl/library/axi_ad3552r/index.html
>  
>  properties:
>    compatible:
>      enum:
>        - adi,axi-dac-9.1.b
> +      - adi,axi-ad3552r
>  
>    reg:
>      maxItems: 1
> @@ -41,22 +43,54 @@ properties:
>    '#io-backend-cells':
>      const: 0
>  
> +  '#address-cells':
> +    const: 1
> +
> +  '#size-cells':
> +    const: 0
> +
>  required:
>    - compatible
>    - dmas
>    - reg
>    - clocks
>  
> +patternProperties:
> +  "^.*@([0-9])$":
> +    type: object
> +    additionalProperties: true
> +    properties:
> +      io-backends:
> +        description: |
> +          AXI backend reference
> +    required:
> +      - io-backends
> +
>  additionalProperties: false
>  
>  examples:
>    - |
>      dac@...00000 {
> -        compatible = "adi,axi-dac-9.1.b";
> -        reg = <0x44a00000 0x10000>;
> -        dmas = <&tx_dma 0>;
> +      compatible = "adi,axi-dac-9.1.b";
> +      reg = <0x44a00000 0x10000>;
> +      dmas = <&tx_dma 0>;

If it makes sense to reformat then separate patch
please as this is hard to read as a result of this
change.  Also, as pointed out, be consistent with spacing.

> +      dma-names = "tx";
> +      #io-backend-cells = <0>;
> +      clocks = <&axi_clk>;
> +    };
> +
> +  - |
> +    axi_dac: spi@...70000 {
> +        compatible = "adi,axi-ad3552r";
> +        reg = <0x44a70000 0x1000>;
> +        dmas = <&dac_tx_dma 0>;
>          dma-names = "tx";
>          #io-backend-cells = <0>;
>          clocks = <&axi_clk>;
> +
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        /* DAC devices */
>      };
>  ...
>