Re: [PATCH v2 6/6] iio: adc: ti-ads1298: add ADS1299 support

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 27 Oct 2026 23:26:52 -0300
Stephan Costa Barros <stephanbrrs8@gmail.com> wrote:

> On Sun, 25 Oct 2026 23:34:29 +0000, Jonathan Cameron wrote:
> > A few things in here feel like they should be in precursor
> > patches because the implication is they apply just as much
> > to improving support for the ads1298 as they do for the
> > new device.  
> 
> Agreed. DVDD and PWDN become ADS129x patches, binding and driver, before
> the ADS1299 ones.
> 
> > > +	if (FIELD_GET(ADS1299_MASK_ID_DEVICE, id) != ADS1299_ID_DEVICE ||
> > > +	    nu_ch > 2)
> > > +		return dev_err_probe(dev, -ENODEV, "Unknown ID: 0x%x\n", id);  
> > How do backwards compatible parts with fallback compatible of ads1299 work?
> >
> > Generally we don't reject on simply an who am I value mismatch.
> > Note the existing driver may need relaxing on that point - we used
> > to do this before DT maitainers pointed out what it broke!  
> 
> Today that works only within a family: the channel count comes from the
> ID, so ti,ads1299 serves the -4 and -6, and ti,ads1298 the ADS1294/6
> and the R parts. A part with a new ID is refused, as the existing driver
> does too.
> 
> For v3 I'd do, in a precursor patch for the existing driver: the
> compatible's chip info is what the driver trusts. If the ID is a known
> part of that family, it still gives the channel count and the name; if
> not (another family, or a reserved channel code), the driver warns and
> goes on with the compatible's chip info. The channel count from the ID
> has to stay, since ti,ads1298 has been the only compatible and existing
> boards with an ADS1294 or ADS1296 depend on it.
> 
> Does that match what you have in mind?

Yes. That sounds like the best way to handle this mix of
discoverable and not.

> 
> > > +	/* The ADS1299 comes out of reset with its inputs shorted */  
> >
> > What is the case for the ADS1298 - is this just harmless or does
> > that have similar behavior?  
> 
> Harmless. On the ADS129x CHnSET resets to 00h, normal electrode input,
> so the write changes nothing. On the ADS1299 it resets to 61h, input
> shorted, and without the write each channel reads its own shorted input.
> I'll make it ADS1299 only, through chip info, unless you prefer it
> unconditional.
> 
> > > +	for (i = 0; i < indio_dev->num_channels; i++) {  
> >
> > 	for (unsigned int i = 0;...  
> 
> Will do.
> 
> Thanks,
> Stephan
>