aarch64 grub serial output

[Peter Geis]

Good Morning,

I have an arm64 rk3399-rockpro64 that I am booting from u-boot to grub-efi.
The boot path works fine, but I am unable to get the serial terminal working.

I get the following output only:
error: serial port `com2' isn't found.
error: terminal `serial' isn't found.
error: terminal `serial' isn't found.
EFI stub: Booting Linux Kernel...
EFI stub: EFI_RNG_PROTOCOL unavailable, no randomness supplied
EFI stub: ERROR: Could not determine UEFI Secure Boot status.
EFI stub: Using DTB from configuration table
EFI stub: Exiting boot services and installing virtual address map...
[    0.000000] Booting Linux on physical CPU 0x0000000000 [0x410fd034]

Here is my grub config, including the kernel command line showing a
working serial output:
GRUB_CMDLINE_LINUX_DEFAULT="earlycon=uart8250,mmio32,0xff1a0000
console=tty0 console=ttyS2,1500000n8"
GRUB_TERMINAL="console serial"
GRUB_SERIAL_COMMAND="serial --speed=1500000 --unit=2 --word=8
--parity=no --stop=1"

I see I the console errors on the serial connection passed from
u-boot, but I can't figure out how to get a full console there.
Any suggestions would be greatly appreciated.

Thanks,
Peter