Re: [PATCH 8/8] dt-bindings: hwmon: allow specifying channels for tmp421

[Guenter Roeck <linux@roeck-us.net>]

On Wed, Sep 22, 2021 at 09:22:33AM +0200, Krzysztof Adamski wrote:
> Dnia Tue, Sep 21, 2021 at 05:58:31AM -0700, Guenter Roeck napisał(a):
> > > 
> > > ti,n-factor
> > 
> > n-factor isn't just supported by TI sensors, though it isn't always called
> > n-factor. Maxim (eg MAX6581) uses the term "ideality factor", though they
> > also refer to the factor as "N" in the datasheet.
> > 
> > So question is if we make this ti,n-factor and maxim,n-factor, or if we make
> > it generic and define some kind of generic units. Thoughts ? My personal
> > preference would be a generic definition, but is not a strong preference.
> 
> That was exactly my way of thinking here - many sensors have n-factor
> parameter and this is the name I see most often.
> 
> That being said, maybe it should be "nfactor" instead of "n-factor", as
> this is what tmp513 is using?
> 
> > In regard to units, the n-factor is, as the name says, a factor. Default
> > value is 1.008. The value range for MAX6581 is 0.999 to 1.030. For TMP421
> > it is 0.706542 to 1.747977. So the scondary question is if the value
> > written should be the register value (as proposed here) or the absolute
> > factor (eg in micro-units).
> 
> Since expressing the fractional values in DT isn't well supported and
> (at least here) hardware guys like to think in terms of register values
> so this is what I proposed. Also, I just noticed that, for example,
> TMP531 is using register values as well.
> 

I never see "someone else does that" as valid argument. Also, DT does
support fractional values, via units. It is perfectly valid to describe
a voltage as micro-volt, for example.

If the agreement is to use raw register values, I think the property name
should be prefixed with the vendor name, since it won't be a standard
property. I'll defer on Rob for that, though.

Thanks,
Guenter