Re: [PATCH 1/2] dt-bindings: iio: adc: ti,ads1298: add ADS1299 EEG ADC variants

[Conor Dooley]

On Wed, Jul 01, 2026 at 12:14:28AM +0100, Jonathan Cameron wrote:
> On Tue, 30 Jun 2026 17:03:10 +0300
> Md Shofiqul Islam <shofiqtest@xxxxxxxxx> wrote:
> 
> > The ADS1299, ADS1299-4, and ADS1299-6 share the same SPI interface
> > and register map as the ADS1298 ECG ADC family but are designed for
> > EEG and biopotential measurement.  Key differences from ADS1298:
> > - PGA gain up to 24x (vs 12x for ADS1298)
> > - Internal reference is always 2.4V (no 4V option)
> > 
> > Add compatible strings and update the vref-supply description to
> > document the ADS1299 reference voltage behaviour.
> > 
> > Signed-off-by: Md Shofiqul Islam <shofiqtest@xxxxxxxxx>
> 
> >  
> >  maintainers:
> >    - Mike Looijmans <mike.looijmans@xxxxxxxx>
> > @@ -17,6 +22,9 @@ properties:
> >    compatible:
> >      enum:
> >        - ti,ads1298
> > +      - ti,ads1299
> > +      - ti,ads1299-4
> > +      - ti,ads1299-6
> 
> As the channel count is a discoverable feature (encoded as a field in the
> ID Register, I think we can use just the one compatible).  FWIW it is
> nice to see a manufacturer making this discoverable!  I'd expect any
> future drop in parts to vary the other part of the ID, but this field
> should be respected - as such this doesn't fall into the stuff I've been
> discussing with DT maintainers about fallback compatibles needing to
> be specific (I'm way behind so not sure where that thread got to!)

I forget that thread too, but I think the difference is discoverable ID
versus discoverable capabilities. If you match on a generic compatible
with a new discoverable ID you've got no idea how to handle it. Matching
on an existing specific compatible with a new ID, you treat it as the
existing device. Matching on a generic compatible with the ability to
discover the channel count, you know what to do.

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