st77xx author here. In my experience the easiest was to look at a few existing drivers which have the initialization sorted out already (e.g. here which is exceptionally cleanly written — don’t know about functionality, did not test), then write it using (new) symbolic constants where it makes sense (e.g. here, checking against the datasheet along the way. Later, you might add things like hardware display orientation (that particular driver has it here). You can use the test st77xx-test.py script (as described here). The last (easy, with st77xx), is to use the driver with LVGL. Good luck.