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

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Message-ID: <Z8DZXAivPexoPJkN@JSANTO12-L01.ad.analog.com>
Date: Thu, 27 Feb 2025 18:30:04 -0300
From: Jonathan Santos <jonath4nns@...il.com>
To: Conor Dooley <conor@...nel.org>
Cc: Jonathan Santos <Jonathan.Santos@...log.com>, 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, 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 02/13, Conor Dooley wrote:
> 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.
> 
We have one internal synchronization source and two external ones.
The internal is when /SYNC_OUT drives /SYNC_IN (in this case with self
referencing). The external sources include using a GPIO to drive the 
/SYNC_IN (sync-in-gpio case) or using an external /SYNC_OUT, the last one
is described in the datasheet for multi-devices setup.

The trigger-sources property is inteded to indicate wheter the /SYNC_OUT
signal originates from within the device or from another source. currently
we are only handling the internal case. We are not sure yet how to handle
the external sources.

> > +    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
> >