linux-kernel - Re: [PATCH v1 01/15] dt-bindings: iio: adc: ad7768-1: add synchronization over SPI property

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Message-ID: <Z4Lx5myE2OPDie6n@JSANTO12-L01.ad.analog.com>
Date: Sat, 11 Jan 2025 19:34:14 -0300
From: Jonathan Santos <jonath4nns@...il.com>
To: David Lechner <dlechner@...libre.com>
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, jic23@...nel.org,
	robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
	marcelo.schmitt1@...il.com
Subject: Re: [PATCH v1 01/15] dt-bindings: iio: adc: ad7768-1: add
 synchronization over SPI property

On 01/07, David Lechner wrote:
> On 1/7/25 9:24 AM, Jonathan Santos wrote:
> > Add adi,sync-in-spi property to enable synchronization over SPI.
> > This should be used in the case when the GPIO cannot provide a
> > pulse synchronous with the base MCLK signal.
> > 
> > User can choose between SPI, GPIO synchronization or neither of them,
> > but only if a external pulse can be provided, for example, by another
> > device in a multidevice setup.
> > 
> 
> While we are fixing up these bindings, we could add some more trivial things,
> like power supplies.
> 
> Also, the interrupt property could use a description since the chip has multiple
> output pins. I assume it means the /DRDY pin?
> 

Right! Yes, the interrupt pin refers to the /DRDY.

> > Signed-off-by: Jonathan Santos <Jonathan.Santos@...log.com>
> > ---
> >  .../bindings/iio/adc/adi,ad7768-1.yaml        | 24 ++++++++++++++++++-
> >  1 file changed, 23 insertions(+), 1 deletion(-)
> > 
> > diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ad7768-1.yaml b/Documentation/devicetree/bindings/iio/adc/adi,ad7768-1.yaml
> > index 3ce59d4d065f..55cec27bfe60 100644
> > --- a/Documentation/devicetree/bindings/iio/adc/adi,ad7768-1.yaml
> > +++ b/Documentation/devicetree/bindings/iio/adc/adi,ad7768-1.yaml
> > @@ -47,6 +47,15 @@ properties:
> >        in any way, for example if the filter decimation rate changes.
> >        As the line is active low, it should be marked GPIO_ACTIVE_LOW.
> >  
> > +  adi,sync-in-spi:
> 
> If this is saying that SYNC_OUT is connected to SYNC_IN, then I think the name
> should be something like adi,sync-in-sync-out. SPI seems irrelevant here since
> we should just be describing how things are wired up, not how it is being used.
> 
> But if we also need to consider the case where SYNC_OUT of one chip is connected
> to SYNC_IN of another chip, we might want to consider using trigger-source
> bindings instead (recently standardized in dtschema).
> 

Do you mean the trigger-sources used for LEDs? I can try to see if it works, but would it
handle the non-GPIO case? While testing a multidevice setup, I found it simpler to 
have a single device to manage everything. It lets us toggle the GPIO or /SYNC_OUT
without referencing another device and makes simultaneous buffered reads easier.

Maybe we could stick to synchronization within the chip for now.

> > +    description:
> > +      Enables synchronization of multiple devices over SPI. This property is
> > +      used when a signal synchronous to the base MCLK signal cannot be provided
> > +      via GPIO. It requires the SYNC_OUT pin to be connected to the SYNC_IN pin
> > +      on the ADC. In the case of multiple devices, the SYNC_OUT pin of one device
> > +      should be routed to the SYNC_IN pins of the other devices.
> > +    type: boolean
> > +
> >    reset-gpios:
> >      maxItems: 1
> >  
> > @@ -65,7 +74,6 @@ required:
> >    - vref-supply
> >    - spi-cpol
> >    - spi-cpha
> > -  - adi,sync-in-gpios
> >  
> >  patternProperties:
> >    "^channel@([0-9]|1[0-5])$":
> > @@ -89,6 +97,20 @@ patternProperties:
> >  allOf:
> >    - $ref: /schemas/spi/spi-peripheral-props.yaml#
> >  
> > +  # adi,sync-in-gpios and adi,sync-in-spi are mutually exclusive (neither is also valid)
> > +  - if:
> > +      required:
> > +        - adi,sync-in-gpios
> > +    then:
> > +      properties:
> > +        adi,sync-in-spi: false
> > +  - if:
> > +      required:
> > +        - adi,sync-in-spi
> > +    then:
> > +      properties:
> > +        adi,sync-in-gpios: false
> 
> I think this can be simplified to using oneOf: to provide XOR validation
> 

Right!

> > +
> >  unevaluatedProperties: false
> >  
> >  examples:
>