You almost certainly want either of the two following branches:
4.19.154(for a 4.19-based system)4.4.15(I believe this was also tested successfully with 4.15.0-46.49 from Ubuntu 18.04 LTS)4.4.241(builds under 4.4.241 and probably works; known not to work under 4.19)
This driver adapts the existing CP210x driver for Linux 4.x to support PPS, such as provided by a USB GPS. This has been tested with the Ubuntu 18.04 LTS 4.15.0-46.49 kernel and a Jackson Labs “Firefly” Global Positioning System Disciplined Oscillator (GPSDO).
It is assumed that this driver works with all 4.x and 5.x kernels, but this has not been proven. This code has diverged significantly from upstream between 2018 and now. Confirmation of correct function with a given kernel will be appreciated!