Re: [Qemu-devel] Re: POST failure (loop) with isapc and seabios

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

On Thu, Nov 26, 2009 at 11:35:52PM +0100, Sebastian Herbszt wrote:
> Maybe the expansion rom bar can be used for pci devices like on real
> hardware. The bios will check it and load the rom itself instead of
> relying on qemu to do the job.

SeaBIOS can pull roms from pci space today.  Long term, I would prefer
to see qemu use this.

> If a soft reset is requested with the goal of a transition from
> protected to real mode and the bios is reloaded, it should not do
> any harm because the internal device states are kept and the cmos
> still has the correct shutdown status code for the transition.

SeaBIOS stores internal state in the f-segment - it wont function
properly if that state is cleared.  (For example, disk read requests
will fail, e820 requests will fail, etc.)

>Bochs
> bios doesn't rely on shadowing so none of its internal state is lost
> either, but the created tables (smbios, mp table, etc.) will be
> gone.

Clearing the tables is also broken (though less likely to be noticed).
In a nutshell, qemu can't reset the f-segment and expect a resume
operation to work.  As Gleb pointed out though, it seems this use case
is more theoretical than practical, so worrying about this may not be
productive.

-Kevin