Re: [PATCH v1 08/13] dt-bindings: iio: adc: adi,ad4134: Document SPI connection mode

[Marcelo Schmitt <marcelo.schmitt1@gmail.com>]

Hello Conor, sorry for delayed reply.

On 09/07, Conor Dooley wrote:
> On Fri, Sep 04, 2026 at 07:06:44PM -0300, Marcelo Schmitt wrote:
> > On 09/04, Marcelo Schmitt wrote:
> > > On 09/03, Conor Dooley wrote:
> > > > On Wed, Sep 02, 2026 at 02:24:02PM -0300, Marcelo Schmitt wrote:
> > > > > Document how AD4134 chips are connected to the host SPI controller
> > > > > according to different wiring configurations.
> > > > > 
> > > > > Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
> > > > > ---
> > > > >  .../bindings/iio/adc/adi,ad4134.yaml          | 22 +++++++++++++++++++
> > > > >  1 file changed, 22 insertions(+)
> > > > > 
> > > > > diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ad4134.yaml b/Documentation/devicetree/bindings/iio/adc/adi,ad4134.yaml
> > > > > index ea6d7e026419..d843c02a394a 100644
> > > > > --- a/Documentation/devicetree/bindings/iio/adc/adi,ad4134.yaml
> > > > > +++ b/Documentation/devicetree/bindings/iio/adc/adi,ad4134.yaml
> > > > > @@ -131,6 +131,28 @@ properties:
> > > > >      enum: [ free-running, gated ]
> > > > >      default: gated
> > > > >  
> > > > > +  adi,spi-mode:
> > > > > +    $ref: /schemas/types.yaml#/definitions/string
> > > > > +    enum: [ no-cs, 4-wire, one-channel-chain, two-channel-chain ]
> > > > > +    description: |
> > > > > +      This property indicates the SPI wiring configuration.
> > > > > +
> > > > > +      When this property is omitted, it is assumed that the device is using
> > > > > +      'no-cs' wiring. When this property is present, it indicates that the
> > > > > +      device is using one of the following wiring configurations:
> > > > 
> > > ...
> > > > I'd also really appreciate a dts example for a system
> > > > with one-channel-chain or two-channel-chain looks, given the second
> > > > device may require different supplies etc. I have no impression in my
> > > > head of how the dt would be constructed, so I'd like to see wht you have
> > > > in mind.
> > > 
> > ...
> > 
> > Realized what I said doesn't make much sense. The peripherals can all have
> > the same configuration and thus share CS, SCLK, and controller SDO. The wiring
> > would be like the following
> > 
> > ::
> > 
> >   +-----------------------+                               +-----------------+
> >   |         AD4134        |                               | SPI Controller  |
> >   |                       |                               |                 |
> >   |                       |                               |                 |
> >   | SPI interface    SCLK |<--------------------+---------| SCLK            |
> >   | for register       CS |<--------------------|-+-------| CS              |
> >   | access            SDI |<--------------------|-|-+-----| SDO             |
> >   |                   SDO |------->|¯¯¯¯\       | | |     |                 |
> >   |                       |        |MUX  >------|-|-|---->| SDI0            |
> >   | Data interface  DOUT0 |------->|____/<------|-|-|---- | GPIO            |
> >   | for ADC sample  DOUT1 |---------------------|-|-|---->| SDI1            |
> >   | data read        DCLK |<-------------+------|-|-|-----| DCLK            |
> >   |                 DOUT2 |<-+           |      | | |     |                 |
> >   |                 DOUT3 |<-|-+         |      | | |     |                 |
> >   |                   ODR |<-|-|---------|--+   | | |  +->| Offload Trigger |
> >   +-----------------------+  | |         |  |   | | |  |  +-----------------+
> >                              | |         |  |   | | |  +--| PWM1            |
> >                              | |         |  +---| | | ----| PWM0            |
> >                              | |         |  |   | | |    +-----------------+
> >                              | |         |  |   | | |
> >   +-----------------------+  | |         |  |   | | |
> >   |         AD4134        |  | |         |  |   | | |
> >   |                       |  | |         |  |   | | |
> >   | SPI interface         |  | |         |  |   | | |
> >   | for register     SCLK |<-|-|---------|--|---+ | |
> >   | access             CS |<-|-|---------|--|---|-+ |
> >   |                   SDI |<-|-|---------|--|---|-|-+
> >   |                   SDO |  | |         |  |   | | |
> >   | Data interface        |  | |         |  |   | | |
> >   | for ADC sample  DOUT0 |--+ |         |  |   | | |
> >   | data read       DOUT1 |----+         |  |   | | |
> >   |                 DOUT2 |<-+           |  |   | | |
> >   |                 DOUT3 |<-|-+         |  |   | | |
> >   |                  DCLK |<-|-|---------+  |   | | |
> >   |                   ODR |<-|-|---------|--+   | | |
> >   +-----------------------+  | |         |  |   | | |
> >                              | |         |  |   | | |
> >                              | |         |  |   | | |
> >                              | |         |  |   | | |
> >   +-----------------------+  | |         |  |   | | |
> >   |         AD4134        |  | |         |  |   | | |
> >   |                       |  | |         |  |   | | |
> >   |                       |  | |         |  |   | | |
> >   | SPI interface    SCLK |<-|-|---------|--|---+ | |
> >   | for register       CS |<-|-|---------|--|-----+ |
> >   | access            SDI |<-|-|---------|--|-------+
> >   |                       |  | |         |  |
> >   | Data interface        |  | |         |  |
> >   | for ADC sample  DOUT0 |--+ |         |  |
> >   | data read       DOUT1 |----+         |  |
> >   |                 DOUT2 |              |  |
> >   |                 DOUT3 |              |  |
> >   |                  DCLK |<-------------+  |
> >   |                   ODR |<----------------+
> >   +-----------------------+
> > 
> > 
> > So we would set them as only one daisy-chained device.
> > 
> >     spi {
> >         ...
> >         adc@0 {
> >             compatible = "adi,ad4134";
> >             reg = <0>;
> >             spi-rx-bus-width = <1>, <1>; /* 2 lanes of 1 bit each */
> > 
> >             <supplies, clock, and other properties ...> 
> > 
> >             #daisy-chained-devices = <2>;
> 
> Does this property actually provide value here? I assume it does because
> otherwise you don't know how many devices there are.

Yes, the number of daisy-chained-devices is needed to determine how much data
to transfer on ADC sample read. We already have some documentation in
Documentation/devicetree/bindings/common-properties.txt

> 
> >             adi,spi-mode = "two-channel-chain";
> 
> How does this interact with spi-rx-bus-width? Is the value of this
> consistent with adi,spi-mode? IOW, for adi,spi-mode = "one.." will there
> only ever be Dout0 connected to the host and for adi,spi-mode = "two.."
> will Dout1 and Dout0 both be connected?

For this particular ADC design, yes.
adi,spi-mode = "one-channel-chain" always expects spi-rx-bus-width = <1> (only DOUT0) and
adi,spi-mode = "two-channel-chain" always expects spi-rx-bus-width = <1>, <1> (DOUT0, DOOUT1).
Though, it is possible to have spi-rx-bus-width = <1> and
spi-rx-bus-width = <1>, <1> in non-chained setups.

Will make the constraints explicit on v2.
allOf:
  ...
  - oneOf:
      - required: [adi,spi-mode, '#daisy-chained-devices']
        properties:
          adi,spi-mode:
            const: one-channel-chain
          spi-rx-bus-width:
            maxItems: 1
      - required: [adi,spi-mode, '#daisy-chained-devices']
        properties:
          adi,spi-mode:
            const: two-channel-chain
          spi-rx-bus-width:
            minItems: 2
            maxItems: 2
      - properties:
          '#daisy-chained-devices': false


Best regards,
Marcelo