[SeaBIOS] Proper support for PCI-based option rom loading (was Re: [Qemu-devel] Re: qdev property bug?)
anthony at codemonkey.ws
Tue Dec 15 22:41:02 CET 2009
Michael S. Tsirkin wrote:
> On Tue, Dec 15, 2009 at 01:35:52PM -0600, Anthony Liguori wrote:
>> Gerd Hoffmann wrote:
>>> -kernel didn't work on a quick test.
>> Thinking about how to fix this, we have two options.
> Hmm, can you pls explain why it stops working?
Sure. SeaBIOS loads roms in a few ways.
If CONFIG_OPTIONROMS_DEPLOYED, then SeaBIOS scans the 0xc0000..0xf0000
region for anything that looks like a rom. This is how Bochs did it and
is what qemu supports. This is not how modern systems work though.
Modern systems (SeaBIOS with !CONFIG_OPTIONROMS_DEPLOYED), walk the PCI
bus and look for any device with a PCI_ROM_ADDRESS that maps a valid
option rom. It will map the rom in PCI memory and run it's init
function. The rom can use PMM to allocate temporary memory to
reorganize itself. During this time, the rom area is writable. The rom
will create a stub that's usually pretty small that gets loaded by the
BIOS after init into the 0xc0000..0xf0000 region.
So when !CONFIG_OPTIONROMS_DEPLOYED, SeaBIOS does look in this region
for roms because it maps them all from the actual PCI devices.
SeaBIOS can also load roms from up to two fixed physical addresses (when
!CONFIG_OPTIONROMS_DEPLOYED) or from a CBFS payload.
BTW, I'm pretty sure this style of option rom loading (from a PCI
device) is going to be required for device passthrough if we want to
support running those roms in the guests. In fact, it should Just Work
with my patches !CONFIG_OPTIONROMS_DEPLOYED in SeaBIOS.
>> Anthony Liguori
> Will be a problem for non-PCI systems?
You mean, non-PCI x86 systems? I think -m isapc is mainly used for dos
guests. I don't think it's really useful in combination with -kernel
and certainly not for extboot.
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