Comment 6 for bug 1770962

At the grub level, this appears to be sufficient to let grub auto-configure its display on both graphical and serial console:

  serial
  terminal_input serial console
  terminal_output serial console

("terminal_{in,out}put" take a list as arguments)

Works in testing for me in a VM with either UEFI (ovmf) or BIOS (seabios).

Is there any reason for us not to configure this by default on x86 in GRUB? (Not just for the installer image specifically; the serial console autodetection would appear to be based on the firmware interfaces Adam mentions, so should be equally safe generally) Maybe we should turn it on for the subiquity image first, then gather feedback? OTOH what's the worst that happens if we try to use a wrong serial device as a console from within GRUB?