Re: [PATCH 0/4] iio: adc: new ti-ads112c14 driver

[Jonathan Cameron <jic23@kernel.org>]

On Sun, 21 Jun 2026 19:32:29 -0500
"Kurt Borja" <kuurtb@gmail.com> wrote:

> On Sun Jun 21, 2026 at 2:14 PM -05, Jonathan Cameron wrote:
> > On Tue, 16 Jun 2026 13:16:46 -0500
> > David Lechner <dlechner@baylibre.com> wrote:
> >  
> >> On 6/16/26 12:26 PM, Kurt Borja wrote:  
> >> > On Tue Jun 16, 2026 at 10:21 AM -05, David Lechner wrote:    
> >> >> On 6/15/26 7:18 PM, Kurt Borja wrote:    
> >> >>> On Mon Jun 15, 2026 at 4:59 PM -05, David Lechner (TI) wrote:    
> >> 
> >> ...
> >>   
> >> >>>> All of these chips have in common that they are designed for use with
> >> >>>> RTDs and thermocouples and so they look very similar to each other in
> >> >>>> terms of wiring and feature set, even if the register maps are
> >> >>>> different. They are in the gray area where we could either keep them
> >> >>>> separate because they are just different enough, or we could do like
> >> >>>> we've done before with ad_sigma_delta and have a bit of an abstraction
> >> >>>> layer for the register differences and otherwise try to share as much
> >> >>>> code as possible. Normally, I would lean towards keeping them separate,
> >> >>>> but in this case, I'm considering trying to share code because the
> >> >>>> devicetree bindings for the inputs is complex and is going to be mostly
> >> >>>> the same across all of these chips.    
> >> >>>
> >> >>> The channel configuration is indeed very similar for the three chips.
> >> >>> All three have IDAC, BOC and VREF configurations.    
> >> >>
> >> >> Hmm... I forgot to include the burnout current in the DT bindings. Following
> >> >> the channel = "conditions for measurement" pattern that I have set out here
> >> >> I guess that would mean that we would need to have the same inputs twice
> >> >> when using the burnout. One "channel" would be the one used to do a "precision"
> >> >> measurement and the other would be the one to do open/short circuit detection.
> >> >>
> >> >>
> >> >>     i2c {
> >> >>         #address-cells = <1>;
> >> >>         #size-cells = <0>;
> >> >>
> >> >>         adc@40 {
> >> >>             compatible = "ti,ads112c14";
> >> >>             reg = <0x40>;
> >> >>
> >> >>             avdd-supply = <&avdd>;
> >> >>             dvdd-supply = <&dvdd>;
> >> >>
> >> >>             refp-supply = <&avdd>;
> >> >>
> >> >>             #address-cells = <1>;
> >> >>             #size-cells = <0>;
> >> >>
> >> >>             channel@0 {
> >> >>                 reg = <0>;
> >> >>                 diff-channels = <1>, <2>;
> >> >>                 excitation-channels = <0>, <3>;
> >> >>                 excitation-current-microamp = <500>;
> >> >>                 current-chopping;
> >> >>                 ti,vref-source = <ADS112C14_VREF_SOURCE_EXTERNAL>;
> >> >>                 label = "rtd-precision";
> >> >>             };
> >> >>
> >> >>             channel@1 {
> >> >>                 reg = <0>;
> >> >>                 diff-channels = <1>, <2>;
> >> >>                 excitation-channels = <0>, <3>;
> >> >>                 excitation-current-microamp = <500>;  
> > Maybe use an example with more stuff changing? Do we want same excitation
> > for burn out? I've no idea.
> >  
> >> >>                 burnout-current-nanoamp = <1000>;
> >> >>                 ti,vref-source = <ADS112C14_VREF_SOURCE_EXTERNAL>;
> >> >>                 label = "rtd-diagnostic";
> >> >>             };    
> >> > 
> >> > This would mean we wouldn't be able to use iio_chan_spec .channel and
> >> > .channel2 to describe inputs because of duplicate sysfs attributes, no?
> >> >     
> >> 
> >> Yes, that is a bit unfortunate. At least there the labels to tell them
> >> apart. I guess we would just need to use consecutive channel and channel2
> >> when dynamically allocating the channels to avoid conflict.   
> >
> > From a very initial look, maybe do something similar to the folk have
> > been looking at for the more complex DDS devices where we have lots
> > of channels that are on the same 'wires'.  Basically add a numbering
> > scheme to keep them reasonably separate - channel numbers are cheap.
> > Maybe first channel is 10->1f, second 20-2f etc.  They are differential
> > so it will get ugly.  Perhaps have a play around and see if there is
> > a reasonable channel naming scheme for this 'same inputs, different thing
> > being measured case'  
> 
> May I also suggest having some sort of IIO_VOLTAGE_DIAGNOSTIC channel
> type? Would that be worth the trouble?

Nope. That would get messy fast as any channel type could have a diagnostic
variant.   If we only ever want to poll it from sysfs we could use
an info_mask element so in_voltageX_burnoutraw or something like that.

> 
> We could also maybe just drop burn-out current completely from
> dt-bindings and add IIO_CHAN_INFO_BURNOUT_CURRENT. Given that this
> feature is only used ocasionally for diagnostic purposes (I assume...).

I did wonder if we just push this either into debugfs, or into an
events type interface.  So poll it every now and then or on demand.

>