linux-kernel - Re: [PATCH v2 2/4] dt-bindings: iio: adc: add AD4695 and similar ADCs

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Date: Tue, 18 Jun 2024 14:29:10 -0500
From: David Lechner <dlechner@...libre.com>
To: Jonathan Cameron <jic23@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>
Cc: Michael Hennerich <michael.hennerich@...log.com>,
 Nuno Sá <nuno.sa@...log.com>,
 Jonathan Corbet <corbet@....net>, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org
Subject: Re: [PATCH v2 2/4] dt-bindings: iio: adc: add AD4695 and similar ADCs

On 6/17/24 2:53 PM, David Lechner wrote:
> Add device tree bindings for AD4695 and similar ADCs.
> 
> Signed-off-by: David Lechner <dlechner@...libre.com>
> ---
> 
...

> +
> +  interrupts:
> +    minItems: 1
> +    items:
> +      - description:
> +          Signal coming from the BSY_ALT_GP0 or GP3 pin that indicates a busy
> +          condition.
> +      - description:
> +          Signal coming from the BSY_ALT_GP0 or GP2 pin that indicates an alert
> +          condition.
> +
> +  interrupt-names:
> +    minItems: 1
> +    items:
> +      - const: busy
> +      - const: alert
> +

Since the interrupt can come from two different pins, it seems like we would
need an extra property to specify this. Is there a standard way to do this?

Otherwise I will add something like:

adi,busy-on-gp3:
  $ref: /schemas/types.yaml#/definitions/flag
  description:
    When present, the busy interrupt is coming from the GP3 pin, otherwise
    the interrupt is coming from the BSY_ALT_GP0 pin.
   
adi,alert-on-gp2:
  $ref: /schemas/types.yaml#/definitions/flag
  description:
    When present, the alert interrupt is coming from the GP2 pin, otherwise
    the interrupt is coming from the BSY_ALT_GP0 pin.
   

> +
> +patternProperties:
> +  "^channel@[0-9a-f]$":
> +    type: object
> +    $ref: adc.yaml
> +    unevaluatedProperties: false
> +    description:
> +      Describes each individual channel. In addition the properties defined
> +      below, bipolar from adc.yaml is also supported.
> +
> +    properties:
> +      reg:
> +        maximum: 15
> +
> +      diff-channels:
> +        description:
> +          Describes inputs used for differential channels. The first value must
> +          be an even numbered input and the second value must be the next
> +          consecutive odd numbered input.
> +        items:
> +          - minimum: 0
> +            maximum: 14
> +            multipleOf: 2
> +          - minimum: 1
> +            maximum: 15
> +            not:
> +              multipleOf: 2

After some more testing, it turns out that I misunderstood the datasheet and
this isn't actually fully differential, but rather pseudo-differential.

So when pairing with the next pin, it is similar to pairing with the COM pin
where the negative input pin is connected to a constant voltage source.

> +
> +      single-channel:
> +        minimum: 0
> +        maximum: 15
> +
> +      common-mode-channel:
> +        description:
> +          Describes the common mode channel for single channels. 0 is REFGND
> +          and 1 is COM. Macros are available for these values in
> +          dt-bindings/iio/adi,ad4695.h.
> +        minimum: 0
> +        maximum: 1
> +        default: 0

So I'm thinking the right thing to do here go back to using reg and the INx
number and only have common-mode-channel (no diff-channels or single-channel).

common-mode-channel will need to be changed to allow INx numbers in addition
to COM and REFGND.

This means that [PATCH v2 1/4] "dt-bindings: iio: adc: add common-mode-channel
dependency" would be wrong since we would be using common-mode-channel without
single-channel.

It also means we will need an optional in1-supply: true for all odd numbered
inputs.