linux-kernel - Re: [PATCH 1/2] dt-bindings: iio: adc: adding MCP3564 ADC

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Message-ID: <20230520142032.1dc7d593@jic23-huawei>
Date:   Sat, 20 May 2023 14:20:32 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     <marius.cristea@...rochip.com>
Cc:     <lars@...afoo.de>, <robh+dt@...nel.org>,
        <linux-iio@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] dt-bindings: iio: adc: adding MCP3564 ADC

On Fri, 19 May 2023 19:01:44 +0300
<marius.cristea@...rochip.com> wrote:

> From: Marius Cristea <marius.cristea@...rochip.com>
> 
> This is the device tree schema for iio driver for
> Microchip family of 153.6 ksps, Low-Noise 16/24-Bit
> Delta-Sigma ADCs with an SPI interface.
> 
> Signed-off-by: Marius Cristea <marius.cristea@...rochip.com>

Hi Marius,

A few comments inline 
> ---
>  .../bindings/iio/adc/microchip,mcp3564.yaml   | 88 +++++++++++++++++++
>  1 file changed, 88 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/adc/microchip,mcp3564.yaml
> 
> diff --git a/Documentation/devicetree/bindings/iio/adc/microchip,mcp3564.yaml b/Documentation/devicetree/bindings/iio/adc/microchip,mcp3564.yaml
> new file mode 100644
> index 000000000000..407a125e3776
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/adc/microchip,mcp3564.yaml
> @@ -0,0 +1,88 @@
> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/iio/adc/microchip,mcp3564.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Microchip MCP346X and MCP356X ADC Family
> +
> +maintainers:
> +  - Marius Cristea <marius.cristea@...rochip.com>
> +
> +description: |
> +   Bindings for the Microchip family of 153.6 ksps, Low-Noise 16/24-Bit
> +   Delta-Sigma ADCs with an SPI interface.
> +
> +properties:
> +  compatible:
> +    enum:
> +      - microchip,mcp3461
> +      - microchip,mcp3462
> +      - microchip,mcp3464
> +      - microchip,mcp3461r
> +      - microchip,mcp3462r
> +      - microchip,mcp3464r
> +      - microchip,mcp3561
> +      - microchip,mcp3562
> +      - microchip,mcp3564
> +      - microchip,mcp3561r
> +      - microchip,mcp3562r
> +      - microchip,mcp3564r
> +
> +  reg:
> +    maxItems: 1
> +
> +  spi-max-frequency: true
If there is a device constraint on this (normally is) then good to enforce it
from the binding.  Naturally wiring / host side limits may constrain it more.

> +
> +  spi-cpha: true
> +
> +  spi-cpol: true
> +
> +  vref-supply:
> +    description:
> +      Some devices have a specific reference voltage supplied on a different
> +      pin to the other supplies. Needed to be able to establish channel scaling
> +      unless there is also an internal reference available (e.g. mcp3564r)
> +

From a quick glance at a random datasheet, looks like there additional power supplies
that should be required.

If this is required for some devices, I'd expect to see the binding enforce
that with some required entries conditioned on the compatibles rather than as
documentation. If there are devices where it isn't even optional then the binding
should enforce that as well.

> +  microchip,hw-device-address:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    minimum: 0
> +    maximum: 3
> +    description:
> +      The address is set on a per-device basis by fuses in the factory,
> +      configured on request. If not requested, the fuses are set for 0x1.
> +      The device address is part of the device markings to avoid
> +      potential confusion. This address is coded on two bits, so four possible
> +      addresses are available when multiple devices are present on the same
> +      SPI bus with only one Chip Select line for all devices.
> +
> +  "#io-channel-cells":
> +    const: 1
> +
> +dependencies:
> +  spi-cpol: [ spi-cpha ]
> +  spi-cpha: [ spi-cpol ]
> +
> +required:
> +  - compatible
> +  - microchip,hw-device-address
Supplies should also be required (unless optional like vref seems to sometimes
be for these parts - where it's required I expect the binding to enforce that.)
> +
> +additionalProperties: false
For SPI devices, the newer way of providing standard SPI properties is:

allOf:
  - $ref: /schemas/spi/spi-peripheral-props.yaml#

unevaluatedProperties: false

https://elixir.bootlin.com/linux/v6.4-rc1/source/Documentation/devicetree/bindings/iio/adc/adi,ad7298.yaml#L33
for example

> +
> +examples:
> +  - |
> +    spi {
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        adc@0 {
> +            compatible = "microchip,mcp3564r";
> +            reg = <0>;
> +            vref-supply = <&vref_reg>;
> +            spi-cpha;
> +            spi-cpol;
> +            spi-max-frequency = <10000000>;
> +            microchip,hw-device-address = <1>;
> +        };
> +    };
> +...