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

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Message-ID: <418a8a9b-3bcf-4b8f-92a0-619a3bf26ab5@baylibre.com>
Date: Mon, 23 Sep 2024 17:50:24 +0200
From: Angelo Dureghello <adureghello@...libre.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Lars-Peter Clausen <lars@...afoo.de>,
 Michael Hennerich <Michael.Hennerich@...log.com>,
 Nuno Sa <nuno.sa@...log.com>, Jonathan Cameron <jic23@...nel.org>,
 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
Subject: Re: [PATCH v3 04/10] dt-bindings: iio: dac: ad3552r: add io-backend
 support

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@...libre.com>
>>
>> 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@...libre.com>
>> ---
>>   .../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@...70000 {
>> +        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