Hi Geoffroy. 

In your tested device (NUC6CAYH), how to set a serial port to debug the hypervisor? 
Can you show me an example? 

Did you put the serial port address in the efibootmgr command? (uart=xxxx)

efibootmgr -c -l "\EFI\acrn\acrn.efi" -d /dev/sda -p 1 -L "ACRN NUC Hypervisor" \
      -u "bootloader=\EFI\org.clearlinux\bootloaderx64.efi uart=disabled"

Thank you.
Taekyoung Kim