feat: pisugar 2 kernel module

pisugar-module/pisugar-2/Makefile

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+TARGET = pisugar_2_battery
+
+obj-m += pisugar_2_battery.o
+
+KERN_VER = $(shell uname -r)
+
+SOURCEDIR = $(shell pwd)
+BUILDDIR = $(shell pwd)/build
+
+I2C_BUS ?= 0x01
+I2C_ADDR ?= 0x75
+BAT_MODEL ?= 0
+
+all:
+	make -C /lib/modules/$(KERN_VER)/build M=$(SOURCEDIR) modules
+
+clean:
+	rm -f *.cmd *.ko *.o Module.symvers modules.order *.mod.c .pisugar_2_battery.* .modules.* .Module.symvers.* pisugar_2_battery.mod
+
+install: all
+	cp -f pisugar_2_battery.ko /lib/modules/$(KERN_VER)/kernel/drivers/power/supply
+	grep -q pisugar_2_battery /etc/modules || sed -i '$$a pisugar_2_battery' /etc/modules
+	echo "options pisugar_2_battery i2c_bus=$(I2C_BUS) i2c_addr=$(I2C_ADDR) bat_model=$(BAT_MODEL)" > /etc/modprobe.d/pisugar_2_battery.conf
+	depmod -a
+	modprobe pisugar_2_battery
+
+uninstall:
+	rmmod pisugar_2_battery || true
+	rm -f /lib/modules/$(KERN_VER)/kernel/drivers/power/supply/pisugar_2_battery.ko
+	sed -i '/pisugar_2_battery/d' /etc/modules
+	rm -f /etc/modprobe.d/pisugar_2_battery.conf

pisugar-module/pisugar-2/README.md

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+# PiSugar Linux kernel modules
+
+Linux kernel modules for PiSugar 2.
+
+## Preparing for building RPI kernel module
+
+### Linux distributions with kernel symbols
+
+Congratulations if your PI is running a linux distribution that has `/lib/modules/$(uname -r)/build/` directory, e.g. ubuntu-server or latest pi os, you don't need to manually build RPI kernel, and that will save a lot of time.
+
+Install `build-essential` and `linux-headers`
+```shell
+sudo apt install -y build-essential linux-headers-$(uname -r)
+```
+
+Running 32bit OS in a 64bit machine, see [this](https://forums.raspberrypi.com/viewtopic.php?t=367669).
+
+### Old raspberry Pi OS
+
+As kernel symbols is not included in Raspberry Pi OS (no `/lib/modules/$(uname -r)/build`), so you need to compile the kernel and generate the kernel symbols by yourself. 
+
+To build the kernel, see official doc: https://www.raspberrypi.com/documentation/computers/linux_kernel.html
+
+## Compile/install/uninstall kernel module
+
+Clone this repository, make kernel modules:
+```shell
+make
+```
+
+Install:
+```shell
+sudo make install
+```
+
+Module params:
+```
+i2c_bus     i2c bus, default 0x01
+i2c_addr    i2c addr, default 0x75
+bat_model   PiSugar2 model, 0 (for pi zero) or 1 (pro for pi 3/4)
+```
+
+Install with parameters:
+```shell
+sudo make install i2c_bus=0x01 i2c_addr=0x75 bat_model=0
+```
+
+Uninstall:
+```shell
+sudo make uninstall
+```
+
+## Manually load kernel module
+
+Load module:
+```shell
+sudo insmod pisugar_2_battery.ko
+# or
+sudo insmod pisugar_2_battery.ko i2c_bus=1 i2c_addr=0x75 bat_model=0
+```
+
+Now, it is loaded:
+```shell
+lsmod | grep battery
+```
+
+And you will see extra device files in `/sys/class/power_supply`
+```shell
+ls /sys/class/power_supply
+```
+
+Remove module:
+```shell
+sudo rmmod pisugar_2_battery.ko
+```
+
+Now, you can enable a battery monitor plugin that reads battery status from power supply subsystem (OS battery monitor plugin or a 3rd party plugin).
+
+If you want to load kernel module at boot time, copy it to `/lib/modules/$(uname -r)/kernel/drivers/power/supply`
+```shell
+sudo cp -f pisugar_2_battery.ko /lib/modules/$(uname -r)/kernel/drivers/power/supply
+sudo echo pisugar_2_battery >> /etc/modules
+sudo depmod -a
+```
+
+You may want to change module parameters:
+```shell
+echo "options pisugar_2_battery i2c_bus=0x01 i2c_addr=0x75 bat_model=0" | sudo tee /etc/modprobe.d/pisugar_2_battery.conf
+```
+
+## License
+
+GPL