[SeaBIOS] Commit d6728f301d7e ("add serial console support") causes double-printing

[Omar Sandoval]

On Thu, Jan 11, 2018 at 10:07:03AM +0100, Gerd Hoffmann wrote:
>   Hi,
> 
> > But instead I get the following mess:
> > 
> >     │  BBoooott  AArrcchh  LLiinnuuxx  ((xx8866__6644))
> 
> Seems both seabios and boot loader print to the serial line.
> 
> > qemu-system-x86_64 -nodefaults -nographic -serial mon:stdio -cpu kvm64 -enable-kvm -boot d -no-reboot -cdrom archlinux-2018.01.01-x86_64.iso
> 
> Try "-display none" instead of "-nographic".
> 
> "-nographic" is a shortcut which does several things, one of them is
> setting the "-machine graphics=off" guest hint, which in turn enables
> the serial console in seabios.

Indeed, that fixes it. Thanks!