[coreboot] [PATCH] x86.c and x86emu/YABEL updates

Stefan Reinauer stepan at coresystems.de
Mon Oct 26 12:53:27 CET 2009

Peter Stuge wrote:
> Stefan Reinauer wrote:
>>>> - YABEL: copy back the IVT, BDA and VBIOS. Some Xorg drivers
>>>>   require this.
>>> Which drivers?
>> As you might imagine I did not test this on the majority of boards,
>> so I can't give a full list of Xorg drivers with the problem,
> Ah, no, of course not, but it would be great to just list the ones
> you know about.
Basically, what happens is that some drivers seem to do BIOS callbacks
to set the display modes.

On x86-64 the VGA option rom is executed in x86emu mode, so strictly
speaking only a vga option rom is needed at 0xc0000.

On x86(-32) systems vm86 is used by Xorg, and the card is (afaik) not
(always) re-initialized, so in addition to that the IVT has to be
intact. With seabios that is always the case, but with x86emu/yabel and
FILO the copying is needed in order to be able to start X. Otherwise the
X server will end itself after unsuccessfully attempting to set a mode.

For the record, this happened to me on a i945 system with onboard
graphics and a not-so-recent debian derivative. Things might be
different with newer Xorgs and kernel mode setting, but I don't know for
sure. Yet, assuming that the VGA option rom and IVT stays intact is
probably fair on an x86 system.


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