[Qemu-devel] Re: Seabios dislikes -M isapc

[Kevin O'Connor <kevin@koconnor.net>]

On Mon, Feb 08, 2010 at 08:09:17PM +0100, Jan Kiszka wrote:
> Sebastian Herbszt wrote:
> > Jan Kiszka wrote:
> >> Hi,
> >>
> >> Seabios seems to have some assumptions built in that break when -M isapc
> >> is selected. Is this supposed to work or is isapc about to die?
> > 
> > SeaBIOS doesn't POST if the F-segment is not writeable [1]. A possible, but IMO
> > wrong fix was posted on the list [2].
> > 
> > [1] http://lists.gnu.org/archive/html/qemu-devel/2009-11/msg01188.html
> > [2] http://lists.gnu.org/archive/html/qemu-devel/2009-12/msg00445.html
> > 
> 
> Indeed, [2] makes it work again.
> 
> But taking away IO_MEM_ROM really looks like a lazy workaround. I don't
> know how much Seabios needs to write - can't it use normal RAM for this?

Handling a read-only f-segment in SeaBIOS would result in significant
code complexity, and some features (like smbios) couldn't be made to
work at all.

I believe it would be far simpler to add a mechanism for
locking/unlocking the f-segment in non-pci mode than it would be to
make seabios work with a read-only f-segment.

Finally, in the normal pci enabled case, both SeaBIOS and bochs bios
will lock the f-segment regardless of how it starts.  So, the patch at
[1] is pretty harmless and it leads to an overall simplification.

-Kevin