[coreboot] SeaBIOS, serial output, and grub

Kevin O'Connor kevin at koconnor.net
Fri May 1 04:26:56 CEST 2009

On Thu, Apr 30, 2009 at 09:18:45PM -0400, Ward Vandewege wrote:
> So - here's the problem with the sgabios approach. Unless I'm
> misunderstanding how this works, using sgabios means that I'd have
> to disable serial in any payload started from grub, as well?

It seems to work fine under qemu.  In any case, a seabios
implementation would have the same issues as sgabios - it would need
to do exactly what sgabios does.

> > > > >   serial --unit=0 --speed=115200 --word=8 --parity=no --stop=1
> > > > >   terminal --timeout=5 serial console

I've reproduced this problem under qemu.  If I boot
qemu/coreboot/seabios/grub, then grub wont use the serial console.
However, if I boot qemu/seabios/grub, then grub seems to work fine.
The above is true regardless of whether SeaBIOS has serial port
debugging on or off.  I guess coreboot is initialzing the serial port
in some way that grub doesn't like.

What's really odd, is that if I have sgabios on, then grub does work
okay.  I didn't catch this last night because I was also playing with
sgabios at the same time.  As a guess, sgabios is reinitializing the
serial port back to a way grub is okay with.  This may be specific to
qemu, but it's something to look into.


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