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

From: Kevin O'Connor
Subject: [Qemu-devel] Re: Seabios dislikes -M isapc
Date: Mon, 8 Feb 2010 19:51:10 -0500
User-agent: Mutt/1.5.20 (2009-08-17)

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.


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