linux-kernel - Re: [PATCH RESEND v3 03/17] dt-bindings: iio: adc: ad7768-1: add trigger-sources property

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Message-ID: <20250213-sympathy-suspend-2c414b383195@spud>
Date: Thu, 13 Feb 2025 20:24:31 +0000
From: Conor Dooley <conor@...nel.org>
To: Jonathan Santos <Jonathan.Santos@...log.com>
Cc: linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, lars@...afoo.de,
	Michael.Hennerich@...log.com, marcelo.schmitt@...log.com,
	jic23@...nel.org, robh@...nel.org, krzk+dt@...nel.org,
	conor+dt@...nel.org, jonath4nns@...il.com,
	marcelo.schmitt1@...il.com, dlechner@...libre.com
Subject: Re: [PATCH RESEND v3 03/17] dt-bindings: iio: adc: ad7768-1: add
 trigger-sources property

On Wed, Feb 12, 2025 at 03:16:16PM -0300, Jonathan Santos wrote:
> In addition to GPIO synchronization, The AD7768-1 also supports
> synchronization over SPI, which use is recommended when the GPIO
> cannot provide a pulse synchronous with the base MCLK signal. It
> consists of looping back the SYNC_OUT to the SYNC_IN pin and send
> a command via SPI to trigger the synchronization.
> 
> Add a new trigger-sources property to enable synchronization over SPI
> and future multiple devices support. This property references the
> main device (or trigger provider) responsible for generating the
> SYNC_OUT pulse to drive the SYNC_IN of device.
> 
> While at it, add description to the interrupts property.
> 
> Signed-off-by: Jonathan Santos <Jonathan.Santos@...log.com>
> ---
> v3 Changes:
> * Fixed dt-bindings errors.
> * Trigger-source is set as an alternative to sync-in-gpios, so we
>   don't break the previous ABI.
> * increased maxItems from trigger-sources to 2.
> 
> v2 Changes:
> * Patch added as replacement for adi,sync-in-spi patch.
> * addressed the request for a description to interrupts property.
> ---
>  .../bindings/iio/adc/adi,ad7768-1.yaml        | 28 +++++++++++++++++--
>  1 file changed, 25 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ad7768-1.yaml b/Documentation/devicetree/bindings/iio/adc/adi,ad7768-1.yaml
> index 3ce59d4d065f..4bcc9e20fab9 100644
> --- a/Documentation/devicetree/bindings/iio/adc/adi,ad7768-1.yaml
> +++ b/Documentation/devicetree/bindings/iio/adc/adi,ad7768-1.yaml
> @@ -26,7 +26,19 @@ properties:
>    clock-names:
>      const: mclk
>  
> +  trigger-sources:
> +    description:
> +      Specifies the device responsible for driving the synchronization pin,
> +      as an alternative to adi,sync-in-gpios. If the own device node is
> +      referenced, The synchronization over SPI is enabled and the SYNC_OUT
> +      output will drive the SYNC_IN pin.

Maybe a silly question, but why is self-reference needed here?
sync-in-gpios is a required property at present, so why can't you
operate under the assumption that neither the trigger-sources when
neither are present? Is it because only one of the sources could be
external and one internal, or there could be either one or two internal
sources? Self-referencing properties always feel like a bit of a
mistake.

> +    maxItems: 2
> +
>    interrupts:
> +    description:
> +      Specifies the interrupt line associated with the ADC. This refers
> +      to the DRDY (Data Ready) pin, which signals when conversion results are
> +      available.
>      maxItems: 1
>  
>    '#address-cells':
> @@ -57,6 +69,9 @@ properties:
>    "#io-channel-cells":
>      const: 1
>  
> +  "#trigger-source-cells":
> +    const: 0
> +
>  required:
>    - compatible
>    - reg
> @@ -65,7 +80,6 @@ required:
>    - vref-supply
>    - spi-cpol
>    - spi-cpha
> -  - adi,sync-in-gpios
>  
>  patternProperties:
>    "^channel@([0-9]|1[0-5])$":
> @@ -89,6 +103,13 @@ patternProperties:
>  allOf:
>    - $ref: /schemas/spi/spi-peripheral-props.yaml#
>  
> +  - oneOf:
> +      - required:
> +          - trigger-sources
> +          - "#trigger-source-cells"
> +      - required:
> +          - adi,sync-in-gpios
> +
>  unevaluatedProperties: false
>  
>  examples:
> @@ -99,7 +120,7 @@ examples:
>          #address-cells = <1>;
>          #size-cells = <0>;
>  
> -        adc@0 {
> +        adc0: adc@0 {
>              compatible = "adi,ad7768-1";
>              reg = <0>;
>              spi-max-frequency = <2000000>;
> @@ -108,7 +129,8 @@ examples:
>              vref-supply = <&adc_vref>;
>              interrupts = <25 IRQ_TYPE_EDGE_RISING>;
>              interrupt-parent = <&gpio>;
> -            adi,sync-in-gpios = <&gpio 22 GPIO_ACTIVE_LOW>;
> +            trigger-sources = <&adc0 0>;
> +            #trigger-source-cells = <0>;
>              reset-gpios = <&gpio 27 GPIO_ACTIVE_LOW>;
>              clocks = <&ad7768_mclk>;
>              clock-names = "mclk";
> -- 
> 2.34.1
> 

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