[U-Boot] [coreboot] U-Boot-x86 / coreboot Integration

[Kevin O'Connor]

On Wed, May 11, 2011 at 02:46:53AM +0200, Peter Stuge wrote:
> Graeme Russ wrote:
> > >> Would be interesting to investigate implementing a stub in U-Boot to
> > >> initialise and use VGA option ROMs
> > >
> > > VGA option ROMs call BIOS functions.  So, one needs a BIOS
> > > implementation (eg, SeaBIOS) or an emulator for them (eg, in
> > > coreboot).
> > 
> > How many functions are needed?
> 
> That depends completely on the particular VGA option ROM.
> 
> Having as complete a BIOS environment as can possibly be accomplished
> is the only hope to making arbitrary option ROMs work.
> 
> Option ROMs are heavily tied into the BIOS concept.
> 
> > (surely not all the IDE and keyboard stuff for example)
> 
> I think I've seen some VGA option ROM get stuck waiting for
> non-working keyboard BIOS services.

One will require all the BIOS interfaces, but the hardware drivers
shouldn't be needed.  So, in SeaBIOS' Kconfig menu, disabling stuff in
"BIOS interfaces" is risky, but one can pretty much disable all the
features under "General Features" and "Hardware support".

> > - Could the bare minimum be implemented in a stripped-down modified
> > SeaBIOS?
> 
> Not really.

Removing the hardware drivers and other niceties can be done.

Note that SeaBIOS is already pretty small (~96K uncompressed / 45K
compressed), so I doubt cutting out features would matter much for
size.  (In a quick test, pulling out everything but interfaces brought
the size to ~45K/24K.)  However, it could be done if one doesn't want
to bother initializing hardware (eg, USB) twice.

-Kevin