linux-kernel - Re: [PATCH v2 02/16] dt-bindings: iio: adc: ad7768-1: add trigger-sources property

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Message-ID: <0044dd4b-01ce-4ca0-9855-8c239b9bfb6f@baylibre.com>
Date: Mon, 27 Jan 2025 19:28:53 -0600
From: David Lechner <dlechner@...libre.com>
To: Jonathan Santos <Jonathan.Santos@...log.com>, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: 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
Subject: Re: [PATCH v2 02/16] dt-bindings: iio: adc: ad7768-1: add
 trigger-sources property

On 1/27/25 9:11 AM, Jonathan Santos wrote:
> Add a new trigger-sources property to enable synchronization across
> multiple devices. This property references the main device (or
> trigger provider) responsible for generating the pulse to drive the
> SYNC_IN of all devices in the setup.
> 
> 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.
> 
> SPI-based synchronization is enabled in the absence of adi,sync-in-gpios
> property. Since adi,sync-in-gpios is not long the only method, remove it
> from required properties.
> 
> While at it, add description to the interrupt property.
> 
> Signed-off-by: Jonathan Santos <Jonathan.Santos@...log.com>
> ---
> 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        | 22 +++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 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..3e119cf1754b 100644
> --- a/Documentation/devicetree/bindings/iio/adc/adi,ad7768-1.yaml
> +++ b/Documentation/devicetree/bindings/iio/adc/adi,ad7768-1.yaml
> @@ -26,7 +26,17 @@ properties:
>    clock-names:
>      const: mclk
>  
> +  trigger-sources:
> +    description:
> +      References the main device responsible for synchronization. In a single
> +      device setup, reference the own node.
> +    maxItems: 1

We probably actually need 2 here. One for /SYNC_IN and one for a GPIO3 pin
acting as the /START signal.

> +
>    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':
> @@ -46,6 +56,8 @@ properties:
>        sampling. A pulse is always required if the configuration is changed
>        in any way, for example if the filter decimation rate changes.
>        As the line is active low, it should be marked GPIO_ACTIVE_LOW.
> +      In the absence of this property, Synchronization over SPI will be
> +      enabled.

Isn't /SYNC_OUT connected to /SYNC_IN required for synchronization over SPI?

If yes, instead of adding this text, I would make the binding have:

oneOf:
  - required:
      - trigger-sources
  - required:
       - adi,sync-in-gpios

>  
>    reset-gpios:
>      maxItems: 1
> @@ -57,6 +69,9 @@ properties:
>    "#io-channel-cells":
>      const: 1
>  
> +  "#trigger-source-cells":
> +    const: 0
> +
>  required:
>    - compatible
>    - reg
> @@ -65,7 +80,8 @@ required:
>    - vref-supply
>    - spi-cpol
>    - spi-cpha
> -  - adi,sync-in-gpios
> +  - trigger-sources
> +  - #trigger-source-cells
>  
>  patternProperties:
>    "^channel@([0-9]|1[0-5])$":
> @@ -99,7 +115,7 @@ examples:
>          #address-cells = <1>;
>          #size-cells = <0>;
>  
> -        adc@0 {
> +        adc0: adc@0 {
>              compatible = "adi,ad7768-1";
>              reg = <0>;
>              spi-max-frequency = <2000000>;
> @@ -109,6 +125,8 @@ examples:
>              interrupts = <25 IRQ_TYPE_EDGE_RISING>;
>              interrupt-parent = <&gpio>;
>              adi,sync-in-gpios = <&gpio 22 GPIO_ACTIVE_LOW>;

Don't we need to drop adi,sync-in-gpios here? I don't think we would have two
things connected to /SYNC_IN at the same time.

> +            trigger-sources = <&adc0>;
> +            #trigger-source-cells = <0>;
>              reset-gpios = <&gpio 27 GPIO_ACTIVE_LOW>;
>              clocks = <&ad7768_mclk>;
>              clock-names = "mclk";