linux-kernel - Re: [PATCH 12/14] dt-bindings: iio: adc: add ad4080

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Message-ID: <6d4e65b9-1392-46e9-ac2e-0c4ef2239fa0@baylibre.com>
Date: Thu, 20 Feb 2025 13:30:11 -0600
From: David Lechner <dlechner@...libre.com>
To: Antoniu Miclaus <antoniu.miclaus@...log.com>, jic23@...nel.org,
 robh@...nel.org, conor+dt@...nel.org, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 12/14] dt-bindings: iio: adc: add ad4080

On 2/20/25 7:54 AM, Antoniu Miclaus wrote:
> Add devicetree bindings for ad4080 family.
> 
> Signed-off-by: Antoniu Miclaus <antoniu.miclaus@...log.com>
> ---
>  .../bindings/iio/adc/adi,ad4080.yaml          | 92 +++++++++++++++++++
>  1 file changed, 92 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/adc/adi,ad4080.yaml
> 
> diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ad4080.yaml b/Documentation/devicetree/bindings/iio/adc/adi,ad4080.yaml
> new file mode 100644
> index 000000000000..e0ea712b8457
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/adc/adi,ad4080.yaml
> @@ -0,0 +1,92 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +# Copyright 2025 Analog Devices Inc.
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/iio/adc/adi,ad4080.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Analog Devices AD4080 20-Bit, 40 MSPS, Differential SAR ADC
> +
> +maintainers:
> +  - Antoniu Miclaus <antoniu.miclaus@...log.com>
> +
> +description: |
> +  The AD4080 is a high speed, low noise, low distortion, 20-bit, Easy Drive,
> +  successive approximation register (SAR) analog-to-digital converter (ADC).
> +  Maintaining high performance (signal-to-noise and distortion (SINAD) ratio
> +  > 90 dBFS) at signal frequencies in excess of 1 MHz enables the AD4080 to
> +  service a wide variety of precision, wide bandwidth data acquisition
> +  applications.
> +
> +  https://www.analog.com/media/en/technical-documentation/data-sheets/ad4080.pdf
> +
> +$ref: /schemas/spi/spi-peripheral-props.yaml#
> +
> +properties:
> +  compatible:
> +    enum:
> +      - adi,ad4080
> +
> +  reg:
> +    maxItems: 1
> +
> +  spi-max-frequency:
> +    maximum: 50000000

Since there are potentially two independent SPI busses on this chip
(one for configuration, one for data) it might be a good idea to put
in a description somewhere that these SPI properties are for the
configuration SPI bus.

> +
> +  clocks:
> +    maxItems: 1
> +
> +  clock-names:
> +    items:
> +      - const: adc-clk

Clocks don't need a name if there is only one clock.

But the description of clocks should say which pin you mean.
Is the the CLK+/- pins or the CNV+/- pins?

> +
> +  vdd33-supply: true
> +
> +  vdd11-supply: true
> +
> +  vddldo-supply: true
> +
> +  iovdd-supply: true
> +
> +  vrefin-supply: true

I would expect we need a vendor boolean property to say if the
DCO+/- pins are wired or not for the echoed clock.

And what does the CNV trigger get wired to? We probably need a
vendor boolean property to say if it is wired to something CMOS
or LVDS. Plus maybe a pwms property or whatever makes sense for
whatever kind of signal generator it is connected to.

> +
> +  adi,num-lanes:
> +    description:
> +      Nmber of lanes on which the data is sent on the output (DA, DB pins).

s/Nmber/Number/

> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    enum: [1, 2]
> +    default: 1
> +

Also, don't we need io-backends for the data interface?

We can also add gpio-controller and #gpio-cells since this
chips provides GPIOs.

> +required:
> +  - compatible
> +  - reg
> +  - clocks

Assuming clocks is CLK+/- pins, this should be optional since
the pins are used for a different function in SPI mode.

> +  - clock-names
> +  - vdd33-supply
> +  - vdd11-supply
> +  - vddldo-supply
> +  - iovdd-supply
> +  - vrefin-supply

The datasheet says things like, "If VDDLDO is connected to a
voltage source, neither VDD11 nor IOVDD should be connected to
any external voltage source.". So making all supplies required
doesn't seem correct.

> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    spi {
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        adc@0 {
> +          compatible = "adi,ad4080";
> +          reg = <0>;
> +          spi-max-frequency = <10000000>;
> +          vdd33-supply = <&vdd33>;
> +          vdd11-supply = <&vdd11>;
> +          vddldo-supply = <&vddldo>;
> +          iovdd-supply = <&iovdd>;
> +          vrefin-supply = <&vrefin>;
> +          clocks = <&adc_clk>;
> +          clock-names = "adc-clk";
> +        };
> +    };
> +...