Re: [Qemu-devel] [PATCH] qemu: piix: PCI bridge ACPI hotplug support

[Michael S. Tsirkin]

On Tue, Jun 11, 2013 at 10:00:36AM +0200, Gerd Hoffmann wrote:
>   Hi,
> 
> > Yes and not just because of windows guests.
> > ACPI spec is also very explicit that native hotplug is an optional
> > feature. Test suites such as WHQL are known to test spec compliance.
> 
> /me looks a bit surprised.
> 
> This pretty much implies that any shpc bridge needs a second interface
> to the hotplug functionality which can be driven via ACPI.  Or the
> firmware somehow handles this using smm (not sure this works for the IRQ
> though).
> 
> Do you know how this is handled by real hardware?
> 
> cheers,
>   Gerd

SHPC is not very widely deployed on a PC.

Since most hardware vendors do care about windows support,
the only way is a separate interface that is driven via ACPI.
You then need an ACPI specific register to switch to standard SHPC.
The SHPC spec even tells you as much.

-- 
MST