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

From: Conor Dooley

Date: Tue Sep 15 2026 - 10:57:28 EST

On Thu, Sep 10, 2026 at 07:19:04PM -0300, Marcelo Schmitt wrote:
> 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@xxxxxxxxxx>
> > > > > > ---
> > > > > > .../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.

If you think that helps, sure. I was mostly asking this for my own
education, because this kind of device is new to me, so that I know what
to expect from future bindings of the same kind (and to have a record on
lore when I inevitably forget).

> allOf:
> ...
> - oneOf:
> - required: [adi,spi-mode, '#daisy-chained-devices']
> properties:
> adi,spi-mode:
> const: one-channel-chain
> spi-rx-bus-width:
> maxItems: 1

Is this enough of a constraint? Someone could still put in
spi-rx-bus-width = <2>...

> - required: [adi,spi-mode, '#daisy-chained-devices']
> properties:
> adi,spi-mode:
> const: two-channel-chain
> spi-rx-bus-width:
> minItems: 2
> maxItems: 2

...or spi-rx-bus-width = <2>, <3> here which conflicts with your
comment above, right?

Prob worth limiting the actual item to 1, if you're gonna add
constraints like this.

> - properties:
> '#daisy-chained-devices': false
>
>
> Best regards,
> Marcelo

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