Re: [Qemu-devel] [PATCH v2 21/21] q35: add acpi-based pci hotplug.

[Jason Baron]

On Thu, Oct 11, 2012 at 10:40:04PM +0200, Michael S. Tsirkin wrote:
> > Windows and Linux guests seem fine with either layout. Slots 1-2 are
> > specific to my setup. So this is a pretty minimal set.
> 
> I guess we can remove the PCI bridge too?
> 

maybe. Perhaps, we can have a very basic set of devices, and have easy
ways to specify various default setups, as I've suggested in a separate
mail.

> One interesting side effect here is that there are less free pci slots
> on root bus now.  I guess at minimum management needs to be taught about
> this, and I'm not sure how.
> 
> > I think that providing the minimal set of devices is good, since it
> > allows the user to configure things as much as possible. So I am in
> > favor of this more minimal set. My only hesitation is that we pull out,
> > or that I have not included some important piece h/w at a specific slot
> > that a guest might need. Thus potentially breaking existing setups.
> > Perhaps, that might mean a new machine type in the future, if we've
> > messed up?
> 
> Yes, that's one solution.
> 
> > These devices and slots are pulled from the Intel docs on ICH9 and Q35
> > specs. See:
> > 
> > http://www.intel.com/content/www/us/en/io/io-controller-hub-9-datasheet.html
> > 
> > Perhaps, Yamahata can comment further on the specific set of bridges?
> > 
> > > It would also be nice to add comments explaining why
> > > specific slots were selected e.g. /* BSD XYZ fails to boot unless ahci is 
> > > at alow 2 */
> > > etc.
> > 
> > Right, its basically just pulled from the Intel spec as mentioned above.
> > 
> > > 
> > > Also - will adding this code now mean that when adding bridges
> > > we'll need to add compatibility code in bios/qemu in the future?
> > > 
> > 
> > I don't think so, but maybe you can elaborate this concern more
> > specifically?
> > 
> > Thanks,
> > 
> > -Jason
> 
> Just this: can same bios work on this interface and the one
> you intend for hotplug behind bridge? Or will we need to version
> interface?
> 

hmm...I wasn't aware of this contraint. Since we control the version of
SeaBIOS in qemu, is this really a problem? And it was suggested that
qemu is the only consumer of the acpi tables.

The current hotplug code doesn't seem to be versioned. Has this caused
problems?

In terms of the interface itself, yes, I think ideally it would be
changed.

Thanks,

-Jason