Re: [PATCH v4 1/2] dt-bindings: iio: adc: ti,ads112c04: Add binding for ADS112C04

On Wed, Aug 12, 2026 at 05:11:35AM +0100, Jonathan Cameron wrote:
> On Wed, 12 Aug 2026 10:53:57 +0800
> Kyle Hsieh <[email protected]> wrote:
> 
> > Hi Conor,
> > 
> > On Wed, Aug 12, 2026 at 12:56 AM Conor Dooley <[email protected]> wrote:
> > >
> > > On Tue, Aug 11, 2026 at 10:48:37AM +0800, Kyle Hsieh wrote:  
> > > > Add device tree binding documentation for Texas Instruments ADS112C04
> > > > I2C Analog-to-Digital Converters.
> > > >
> > > > These devices provide 4-channel, 16-bit delta-sigma ADCs with an I2C
> > > > interface, programmable gain amplifier (PGA), and data-ready (DRDY)
> > > > interrupt output.
> > > >
> > > > The binding uses child nodes to dynamically define the connected
> > > > single-ended or differential channels.
> > > >
> > > > Excitation current, burn-out current, and reference source properties
> > > > are also included to fully describe the chip's hardware capabilities,
> > > > aligned with the ti,ads112c14 binding conventions.
> > > >
> > > > Signed-off-by: Kyle Hsieh <[email protected]>  
> > >  
> > > > +patternProperties:
> > > > +  "^channel@[0-9a-b]$":
> > > > +    $ref: adc.yaml
> > > > +    unevaluatedProperties: false
> > > > +    properties:
> > > > +      reg:
> > > > +        items:
> > > > +          - maximum: 11
> > > > +
> > > > +      single-channel:
> > > > +        maximum: 3  
> > >
> > > Can someone explain to me please why the maximum for this is 3 when reg
> > > goes up to 11? What do the additional reg entries beyond 3 represent?  
> > reg here is just an index for the channel node, not an input pin number.
> > The chip has 12 usable input MUX settings (8 differential pairs and 4
> > single-ended inputs), so at most 12 channel nodes can be described,
> > hence maximum 11.
> > 
> > single-channel refers to the physical analog input pin, and the chip
> > only has AIN0-AIN3, hence maximum 3.
> 
> Exactly as Kyle described - there is no right way to match reg to a property
> when we have mix of single-channel and diff-channels. Hence in this
> one corner case reg is just a magic number - though it may reflect
> ordering of channel acquisition I guess, though we've never documented
> that requirement in a binding.
> 
> We could restrict the differential to be only one direction which would
> give max 10 channels (4 single then 0-1, 0-2, 0-3, 1-2, 1-3, 2-3)
> but there isn't a huge advantage in doing so even though it is trivial
> for software to flip the sign if other direction is wanted.
> 
> Note that we don't actually expect to see all the channels configured,
> it can just be a useful to do things like single ended voltage at
> top of a resistor and differential across the resistor (to get
> allow current to be computed) - so it's not unheard to to mix
> and match.

This kinda thing is what I expected, I just was not sure.

I forget if I have to:
Acked-by: Conor Dooley <[email protected]>
pw-bot: not-applicable

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