The mainline linux does not support the Fintek F819xx chips yes. This repo adds support for Fintek F819xx.
Warning
Not yet tested on Fintek F81804.
Reference:
[1/1] GPIO support for Fintek family F819XX
Both F81804 (64 pins, 30 gpios) and chips F81962/F81964/F81966/F81967
(128 pins, 80 gpios) share the same chip ID, but use a different gpio
mapping. Read the second serial device enable register and test for 0xff
was the recommended method suggested by the chip manufacturer to tell
apart both chips.