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

[Jonathan Cameron <jic23@kernel.org>]

On Fri, 4 Sep 2026 19:06:44 -0300
Marcelo Schmitt <marcelo.schmitt1@gmail.com> 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

That mux in the middle is controlled how?
I'd assume we still have separate chip selects and SDO/SDI shared. So I'd expect
those to be on one SPI bus and the data to be going into separate buses
(maybe all that can be hidden in the backend, not sure).

Or are you suggesting we are just letting all the chained devices see the
same register writes?  That might work I guess with no ability to read any register
state back other than for first device.  If you want to do the
mux magic below you are going to need to treat it as an SPI mux - just with
some lines shared. That means this device ends up split into multiple device
(even if only one ad4134 which is messy).

So to me this has a simple SPI bus, potentially connected to multiple devices
and an IIO backend that deals with DOUT0 etc and the chaining.

Jonathan

> 
> ::
> 
>   +-----------------------+                               +-----------------+
>   |         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>;
> 
>             adi,spi-mode = "two-channel-chain";
>         };
>     };
> 
> Thanks,
> Marcelo