[coreboot] SeaBIOS debug output

[Myles Watson]

> -----Original Message-----
> From: Jordan Crouse [mailto:jordan.crouse at amd.com]
> Sent: Wednesday, July 16, 2008 1:55 PM
> To: Myles Watson
> Cc: Kevin O'Connor; Carl-Daniel Hailfinger; Coreboot
> Subject: Re: SeaBIOS debug output
> 
> On 16/07/08 12:43 -0600, Myles Watson wrote:
> > On Fri, Jul 11, 2008 at 12:51 PM, Kevin O'Connor <kevin at koconnor.net>
> wrote:
> > > On Fri, Jul 11, 2008 at 07:58:35PM +0200, Carl-Daniel Hailfinger
> wrote:
> > >> Can seabios somehow complement x86emu as a way to let certain
> > >> problematic VBIOS images run?
> > >
> > > If you mean run seabios under x86emu - I'm not sure.  Seabios
> > > currently does its initialization in 32bit mode which x86emu may not
> > > like.
> > >
> > > If you mean using seabios to implement the option rom scan - then yes,
> > > I think this is what Stefan suggested and Zhang Rui is working on.  If
> > > I understand correctly, they want to load the seabios blob into ram,
> > > have seabios do its init, run the option roms, and then jump back to
> > > coreboot for the rest of the boot.  Presumably, coreboot would also
> > > use seabios to boot the machine if the user wanted that.
> > >
> > > The thing to be careful of here is making sure coreboot and seabios
> > > don't stomp on each other.  This may not be such a big deal - seabios
> > > doesn't currently write to any ram above 1MiB - if coreboot didn't
> > > write to any ram below 1MiB after launching seabios then maybe it
> > > would work.
> >
> > I for one don't understand what needs to be done in coreboot after the
> > option ROM scans.  It seems like it would help us discuss the possible
> > solutions if we could enumerate that.
> >
> > I don't think the Coreboot->SeaBIOS->Coreboot->Payload route means
> > that SeaBIOS has to return to Coreboot.  It seems like Coreboot can
> > load whatever should come after SeaBIOS into RAM and have SeaBIOS jump
> > there.
> 
> This seems like semantics to me - the jmp will be to an arbitrary
> address - it doesn't really matter if it goes back to coreboot or
> if it goes to the payload.  If it jumped to the payload, SeaBIOS
> will have to be told _where_ to jump anyway, since the payload can
> live anywhere.  All we really need to do is set up an interface to pass a
> address to SeaBIOS, and then its up to coreboot to figure out what
> they want to do after SeaBIOS is done.

My point was that there didn't need to be a preservation of stack state,
global variables, etc.  When I think of a return from a function call, it
seems a lot more complex than jumping to a separate payload.  I thought that
was the problem.

Thanks,
Myles

> Jordan
> 
> --
> Jordan Crouse
> Systems Software Development Engineer
> Advanced Micro Devices, Inc.