I've been building the latest version of the Marlin firmware for my Ender 3 and SKR 1.4 Turbo for a while. I've created two branches in my fork on GitHub, one for a base configuration as close to what Makertech has provided in their AXIS repo, and the other for "enhancements" that I think will make things easier for users.
At the moment I don't have a MKS GEN L V2 board handy so I cannot test these settings until I get my printer. PLEASE BEWARE I TAKE NO RESPONSIBILITY FOR DAMAGED PRINTERS OR BROKEN BOARDS. EVERY ATTEMPT HAS BEEN MADE TO VERIFY THAT EVERYTHING WORKS BUT IT IS UP TO YOU TO INSURE THAT ENDSTOPS AND LIMITS WORK CORRECTLY.
In the future I may turn on volumetric features and linear advance. Please let me know if there is anything you may be interested in enabling or testing.
Compiling and Flashing
For either of these branches you can download the source as a zip file or you can clone the source and switch between any of my branches (including the work I've done on the Ender 3). I've set them up to build using PlatformIO and VSCode. There are tutorials you can find on YouTube. The nice thing is that VSCode is a much, much better IDE compared to the Arduino IDE.
Notes on configuring before building: Stage 09 - Steps 3 - 6 show how to configure the firmware for upgrades you got with your printer. You will still need to make these changes on the base or enhanced branches. The Makertech configuration had the heated bed enabled by default. Both the base and the enhanced branch match this but made no changes with respect to enabling the TMC drivers. If you purchased that upgrade you will need to make those changes. The changes should be the same as what is outlined in the instructions.
If there is interest I would be willing to putting together a version of the Marlin 2.x firmware compiled for the SKR 1.4 Turbo as well. I have a spare board and set of TMC2209 drivers. This will not be a priority until I get my printer, set it up, and have it printing satisfactory. Once I get things working like they should I break them and make them not work so that I can experience the joy of making them work again!