Message-ID: <Z5jx9mJdi3Zh7Mx6@JSANTO12-L01.ad.analog.com>
Date: Tue, 28 Jan 2025 12:04:22 -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,
	marcelo.schmitt@...log.com, jic23@...nel.org, robh@...nel.org,
	krzk+dt@...nel.org, conor+dt@...nel.org, marcelo.schmitt1@...il.com
Subject: Re: [PATCH v2 02/16] dt-bindings: iio: adc: ad7768-1: add
 trigger-sources property

On 01/27, David Lechner wrote:
> 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:
> 

Yes, but the synchronization over SPI is enabled in the absence of the GPIO.
The trigger-sources property would indicate if the sync provider is the
own device or not. As i said below, maybe i misunderstood.

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

Wouldn't be simpler to consider the absence of sync-in-gpio? this way we
have less changes in the ABI.

> >  
> >    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.
> 

I guess i misunderstood the use of trigger-sources. I thought it would
indicate the trigger provider or main device. Like if it points to other
device we should use it to drive the SYNC_IN of all devices.

Then what happens if the trigger-sources points to other node? we would't be
able to driver the SYNC_IN in case of any configuration change?

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

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