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

[Jonathan Santos <jonath4nns@gmail.com>]

On 01/12, Jonathan Cameron wrote:
> On Fri, 10 Jan 2025 18:51:06 -0300
> Marcelo Schmitt <marcelo.schmitt1@gmail.com> wrote:
> 
> > On 01/07, 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.
> > > 
> > > Signed-off-by: Jonathan Santos <Jonathan.Santos@analog.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:
> > > +    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.  
> > So, if I'm getting it right,
> 
> Datasheet on this is indeed complex!
> 
> >/SYNC_IN may be driven by a GPIO (ADAQ7768-1 datasheet Figure 131),
> 
> For that we expose a gpio binding already. If that's present we know what is going on.
> 
> >/SYNC_IN may be driven by own device /SYNC_OUT (ADAQ7768-1 datasheet Figure 133),
> 
> This is the default - no information provided so it isn't wired externally.
> We don't normally bother to describe required chip to chip connections.
> I couldn't entirely figure out if this is 'required' if we aren't driving explicitly
> from GPIO or another chip but i think it is(?).
>

It is. If the device is not being driven by a GPIO or an external
device, the user should connect the /SYNC_OUT to /SYNC_IN. We could
assume that this is the case if the GPIO is not present in the
devicetree, maybe put that into the description. The sync-out-sync-in
property as a boolean can be quite redundant, since we also need to
remove the GPIO.

> >/SYNC_IN may be driven by other AD7768-1 > /SYNC_OUT pin (also Figure 133).
> This is only case we are about for sync in I think.
> 
> As long as there isn't a valid 'not connected' It think we are fine with a boolean.
> 

If opt for a single node instace, thats ok; otherwise, David's
trigger-sources suggestion seems to be the best approach. 

> > That is too much to describe with a boolean.
> > 
> > If David's suggestion of using a trigger-source doesn't fit, this property
> > should at least become an enum or string.
> > 
> > > +    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
> > > +
> > >  unevaluatedProperties: false
> > >  
> > >  examples:
> > > -- 
> > > 2.34.1
> > >   
>