Re: [PATCH 2/2] iio: temperature: ltc2983: Add support for ADT7604

[Nuno Sá]

On Tue, May 12, 2026 at 11:55:20AM +0100, Jonathan Cameron wrote:
> On Tue, 12 May 2026 09:24:27 +0100
> Nuno Sá <noname.nuno@xxxxxxxxx> wrote:
> 
> > On Mon, May 11, 2026 at 12:02:31PM +0000, Stan, Liviu wrote:
> > > On Mon, 11 May 2026 Jonathan Cameron wrote:  
> > > > > > Ok. So what are our options here?  Present it as simple resistance and leave
> > > > > > userspace to figure it out or add a new channel type? To me feels like new
> > > > > > channel type makes sense.  
> > > > >
> > > > > The current approach presents it as IIO_TEMP since the chip outputs coverage
> > > > > (using the custom table interpolation) via the temperature result bank, not
> > > > > the resistance bank, but I agree a new channel type makes sense. Should I
> > > > > create a specific type like IIO_COVERAGE_PERCENT or would a general
> > > > > IIO_PERCENTAGE be better?  
> > > > 
> > > > For ABI purposes we don't care where it comes from.
> > > > 
> > > > We already have some 'ratio' type measurements like concentration which are
> > > > percentages and similar to those I think we need some indication of 'what'
> > > > is being measured given it's unit free.  Hence IIO_COVERAGE_PERCENT seems
> > > > the better choice to me.  
> > > 
> > > Understood. Will do that in v2.  
> > 
> > I do wonder if a complete type is what we want? How will we present it?
> > 
> > in_coverage_ratio?
> > 
> > What I'm not too convinced is that coverage is relative to what? Well
> > it's a percentage so I guess we could not care and leave interpretation to
> > userspace (to know which device is dealing with). Still I wonder if a
> > new iio_chan_info wouldn't be more appropriate? In this case applied to
> > iio_resistance. So something like:
> > 
> > in_resistance_coverage_ratio
> 
> I'm perhaps missing something - as far as I understand it there is no meaningful
> connection to resistance in what is being measured.

Maybe I'm the one missing something but as I understand it is that the
more coverage we have (more liquid in the sensor area), the less
resistance.

> I think what you are proposing is similar to measuring current via voltage
> drop over a sense resistor. We don't present that as modified voltage, we
> present it as current.
>
> Here the thing being measured is coverage rather than resistance
> so keeping resistance in there is confusing for the user.
>

Hmm ok! The above two paragraphs make sense to me. Hard to disagree :)

- Nuno Sá

> If we wanted a type to modify then we could do this as a modified area measurement.
> Channel type IIO_AREA (which is new) and modifier IIO_MOD_RATIO (also new).
> 
> Jonathan
> 
> > 
> > So it's clear what physical quantity coverage ratio is affecting.
> > 
> > Thoughts?
> > - Nuno Sá
> > 
> > > 
> > > Thank you!
> > > 
> > > Liviu  
>