[PATCH v3 3/6] Documentation: DT: Document twl4030-madc-battery bindings

[Dr. H. Nikolaus Schaller]

Am 17.03.2015 um 09:47 schrieb Pavel Machek <pavel at ucw.cz>:

> Hi!
> 
>>>> diff --git a/Documentation/devicetree/bindings/power_supply/twl4030_madc_battery.txt b/Documentation/devicetree/bindings/power_supply/twl4030_madc_battery.txt
>>>> new file mode 100644
>>>> index 0000000..bb3580c
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/power_supply/twl4030_madc_battery.txt
>>>> @@ -0,0 +1,43 @@
>>>> +twl4030_madc_battery
>>>> +
>>>> +Required properties:
>>>> + - compatible : "ti,twl4030-madc-battery"
>>>> + - capacity-uah : battery capacity in uAh
>>> 
>>> Could we make it capacity-uAh ?
>> This name was suggested by Mark Rutland [1] and naming convention
>> should be all lowercase. There exists already bindings
>> without uppercase (e.g. ti,bb-uamp) so I would keep it consistent.
> 
> Messing up SI units due to "convention" is _stupid_. Don't do it.
> 
>>> to introduce coefficients for temperature and discharge rate?
>> What do you mean? Nothing like that is used in current driver why do
>> we need to add it?
> 
> Well, conversion between Li-ion's voltage and state of charge at 0
> current is well known:
> 
>    def percent(m, v):
>    	u = 0.0387-(1.4523*(3.7835-v))
>        if u < 0:
>            return 0
>          return (0.1966+math.sqrt(u))*100

I forgot to ask: does the kernel have a sqrt() function?
> 
> And there's not much to calibrate there, and it should become library
> helper function; there's no need to write it to every single dts.
> 
> The charge/discharge difference is due to internal battery resistance,
> and Ohm's law. (Then, you should not need different values for
> charging/discharging case.)
> 
> With your aproach, you'll get lower percentage when phone is under
> load vs. idle. Taking internal resistance into account would give you
> more precise readings. (Attached, old patch for zaurus shows the
> needed computation).
> 
> And if you wanted even more precise readings... internal resistance
> depends on temperature.
> 
> I guess this should go into library somewhere, because many machines
> need similar code.
> 
> 								Pavel
> -- 
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
> <zbattery.10.diff>