Re: [Qemu-devel] q35 chipset support

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jun 18, 2012 at 03:52:34PM +0200, Markus Armbruster wrote:
> Anthony Liguori <anthony@codemonkey.ws> writes:
> 
> > On 06/15/2012 12:57 PM, Jason Baron wrote:
> >> On Thu, Jun 14, 2012 at 03:16:03PM -0500, Anthony Liguori wrote:
> >>> On 06/14/2012 02:54 PM, Jason Baron wrote:
> >>>> Hi,
> >>>>
> >>>> I recently updated Isaku Yamahata's q35 patches to work on the latest qemu and
> >>>> seabios trees. On the qemu side, most of the changes revolved around updating
> >>>> to use QOM and updates to the memory API. I was also able to drop quite a few
> >>>> patches that had already been resolved by the current qemu tree.
> >>>>
> >>>> The trees seem pretty stable and can be found here:
> >>>>
> >>>> git://github.com/jibaron/q35-qemu.git
> >>>> git://github.com/jibaron/q35-seabios.git
> >>>
> >>> I'm got the beginnings of a feature page started:
> >>>
> >>> http://wiki.qemu.org/Features/Q35
> >>>
> >>> The approach above will not work in a QOM world unfortunately.  We
> >>> need to do quite a bit of ground work before adding another chipset.
> >>> The biggest task is converting devices to not require an ISA bus
> >>> since ICH9 simply doesn't have an ISA bus.
> >>>
> >>
> >> Right, there is no h/w isa bus, but the LPC interface chip is modeled as an isa
> >> bridge. So having an isa bus hanging off of it doesn't seem unreasonable. Unless
> >> there is some more fundamental reason not do it this way?
> >>
> >> It hows up in lspci as:
> >>
> >> 00:1f.0 ISA bridge: Intel Corporation 82801IB (ICH9) LPC Interface
> >> Controller (rev 02)
> >
> > It's not a question of ISA vs. LPC, it's which devices are actually on
> > that bus. See my respond to Markus's note.
> 
> Maybe I'm naive, but platform devices handing off an ISA bus provided by
> that ICH9 ISA bridge looks like a fair approximation to me.  Yes, the
> actual wiring is LPC, but that's a hardware detail invisible to device
> models and guest, isn't it?
> 
> Of course, you can't connect anything but the platform devices to that
> bus.  To connect other ISA devices, you'd have to add a second ISA
> bridge.  I suspect that's what you meant by "You can still have a
> PCI-ISA bridge but the SuperI/O chip is not part of it" elsewhere in
> this thread.
> 
> No idea whether such beasts exist in the physical world, and how they
> work.

See a dump from an old machine of mine (thinkpad T500 FWIW):
it does have an ISA bridge behind the root bus.