On Mon, 16 Apr 2018 16:00:44 +0200
Peter Rosin <p...@axentia.se> wrote:
> On 2018-04-10 17:28, Peter Rosin wrote:
> > +Example:
> > +The system voltage is circa 12V, but divided down with a 22/200
> > +voltage divider to adjust it to the ADC range.
> > +
> > +SYSV ADC GND
> > + + + +
> > + | .-----. | .----. |
> > + '--| 200 |-+-| 22 |--'
> > + '-----' '----'
> > +
> > +sysv {
> > + compatible = "voltage-divider";
> > + io-channels = <&maxadc 1>;
> > +
> > + /* Multiply the ADC voltage by 222/22 to get the system voltage. */
> > + numerator = <222>; /* 200 + 22 */
> > + denominator = <22>;
> > +};
>
> While I already got a reviewed-by from Rob, and maybe I shouldn't be
> stirring the pot, but I had an umpteenth look and I now think this
> one looks a bit odd. It shows a bit that it originates from when the
> compatible was the very generic "io-channel-unit-converter" in v1
> of the series. What I mean is that a voltage divider presumable always
> gets you a lower voltage. Therefore, one would assume that the
> denominator should be larger than the numerator. The fact that this
> translates into the inverted fraction when calculating backwards
> through the voltage divider should probably not affect the binding.
>
> So, in the above example, I think it would make more sense to have
>
> numerator = <22>;
> denominator = <222>; /* 200 + 22 */
>
> (and then, naturally, adjust the driver to invert the fraction)
>
> Comments?
Agreed - it is odd as we currently have it. I wouldn't have
a particular problem with renaming this compatible as voltage
scaler (voltage multiplier has a specific meaning we should avoid
stepping on!) Anyhow, either way is fine with me, but I agree
the current version is odd.
Jonathan
>
> Cheers,
> Peter
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