Comment # 2 on bug 1140464 from Michael Chang

(In reply to Michael Chang from comment #1)
> The aarch64 has no ns8250 (In reply to Oliver Kurz from comment #0)

>  GRUB_SERIAL_COMMAND="serial --unit=0 --speed=115200 --parity=no efi0"  

No. --unit=0 may binds to com0, maybe

 GRUB_SERIAL_COMMAND="serial efi0 --speed=115200 --parity=no"

Test on aarch64 server is really needed to know how it works.