Re: [PATCH v4 2/8] devicetree: power: add battery state machine documentation

[Liam Breck <liam@networkimprov.net>]

On Sun, Jan 29, 2017 at 6:39 PM, Sebastian Reichel <sre@kernel.org> wrote:
> Hi,
>
> On Sun, Jan 29, 2017 at 03:32:10PM -0800, Liam Breck wrote:
>> On Sun, Jan 29, 2017 at 10:06 AM, Sebastian Reichel <sre@kernel.org> wrote:
>> > On Sun, Jan 22, 2017 at 02:22:12PM -0800, Liam Breck wrote:
>> ...
>> >> +Batteries must be referenced by chargers and/or fuel-gauges
>> >> +using a phandle. The phandle's property should be named
>> >> +"monitored-battery".
>> >> +
>> >> +Example:
>> >> +
>> >> +     bat: battery {
>> >> +             compatible = "fixed-battery";
>> >> +             terminate-microvolt = <3700000>;
>> >> +             design-microwatt-hours = <5290000>;
>> >> +             design-microamp-hours = <1430000>;
>> >> +     };
>> >> +
>> >> +     charger: charger@0 {
>> >> +             ....
>> >> +             monitored-battery = <&bat>;
>> >> +             ...
>> >> +     };
>> >> +
>> >> +     fuel_gauge: fuel_gauge@0 {
>> >> +             ....
>> >> +             monitored-battery = <&bat>;
>> >> +             ...
>> >> +     };
>> >
>> > The charger stuff does does not integrate well with
>> > pre-existing support for power-supplies property
>> > described in
>> > Documentation/devicetree/bindings/power/supply/power_supply.txt
>> >
>> > I think the proper chain would be:
>> >
>> > bat: battery {
>> >         compatible = "fixed-battery";
>> >         terminate-microvolt = <3700000>;
>> >         design-microwatt-hours = <5290000>;
>> >         design-microamp-hours = <1430000>;
>> > };
>> >
>> > fuel_gauge: fuel_gauge@0 {
>> >         ...
>> >         monitored-battery = <&bat>;
>> >         power-supplies = <&charger>;
>> >         ...
>> > };
>> >
>> > charger: charger@0 {
>> >         ...
>> > };
>> >
>> > I added the power-supplies node to the fuel-gauge instead of the battery,
>> > since fuel-gauge + fixed-battery is basically a smart battery.
>>
>> BQ24190 charger will need other params from a battery node. How does
>> it get them in this scenario?
>
> It should be able to get all required properties from the bq27xxx.
> Otherwise supporting smart batteries is impossible. What properties
> do you need?

These two, at a minimum:

- precharge-microamps: maximum charge current during precharge
  phase (typically 20% of battery capacity)

- termination-microamps: a charge cycle terminates when the
  battery voltage is above recharge threshold, and the current is below
  this setting (typically 10% of battery capacity)

Sorry, I'm not seeing how the charger will obtain these from the fuel
gauge. Could you clarify with a code snippet?