Linux driver for WinChipHead CH423, a GPIO expander driver

To build:

  make

To load the driver (as root):

  insmod ./ch423.ko

To instantiate the device (as root), replacing XXX with the proper i2c bus:

  echo "ch423 0x24" > /sys/bus/i2c/devices/i2c-XXX/new_device

Note that the i2c address given is meaningless. This device has some severe
limitations and is abusing the i2c protocol. See the comments at the
top of source code.

The GPIOs can then be used with the regular linux tools and interfaces.

A cheap breakout board (US $1.30) is available at:

  https://www.electrodragon.com/product/i2c-to-gpio-io-expander-breaktout-board-ch423/