Trying to improve a kernel driver

[Thomas Marangoni <thomas@xxxxxxxxxxxx>]

Hello,
I'm new to developing kernel drivers and want to improve the driver of 
the axp209 power management chip. I've read the documentation about the 
Linux power supply class 
(https://www.kernel.org/doc/html/latest/power/power_supply_class.html) 
and there it says: "Power supply class is extensible, and allows to 
define drivers own attributes.". The Problem is I couldn't find an 
example of how to add own attributes. My goal is to have an own 
attribute showing up at /sys/class/power_supply/axp20x-battery/

If someone can give me a hint, extended documentation or a better place 
to ask, that would be great!