I got this working in the end.
Basically you need to enable the GPIO by amending the appropriate dts files in the kernel code ( https://github.com/BPI-SINOVOIP/BPI-R2-bsp 1 ) and setting the uart entries to “status=okay”
detalled here: http://fw-web.de/dokuwiki/doku.php?id=en:bpi-r2:gpio 3
Then compile the kernel (in a VM or whereever) and ship it over to the BPI-R2 SD card.
The good news is there is two other options:
frank-w has got pre compiled kernels here, I used 4.4.108. https://drive.google.com/drive/folders/15Y5Y3NAOwg_IMmN3k6hdb7pAQj9oTVTl 1 . just copy over the BPI-BOOT and the BPI-ROOT over to the appropriate partition mounted on other machine as root!
If you prefer 4.14 with uart/gpio enabled in preconfgiured debian images, frank-w has done those too: https://drive.google.com/open?id=15Y5Y3NAOwg_IMmN3k6hdb7pAQj9oTVTl 1
After than just follow the install. use /dev/ttyS2 . make sure setenv and openhab/default have the appropriate entries.
Make sure openhab is added to the tty group.
Sort java out etc…
Good to go - it works well.