Re: [Qemu-devel] [PATCH RFC 0/6] q35: add acpi pci hotplug support

[Marcel Apfelbaum]

On 03/07/2017 19:34, Michael S. Tsirkin wrote:
> On Mon, Jul 03, 2017 at 02:27:11PM +0200, Igor Mammedov wrote:
> > On Fri, 30 Jun 2017 10:25:05 +0300
> > Marcel Apfelbaum <address@hidden> wrote:
> >
> > [...]
> > > So for the modern systems not supporting PCI ACPI hotplug
> > > we don't need pci-bridges anyway, but for the older ones
> > > the ACPI code of the pci-bridge will be loaded into the
> > > ACPI namespace only if a pci-bridge is actually hot-plugged.
> >
> > just note that the set of 'older' guest OSes is limited to
> > one that do not support SHPC (i.e. to EOLed WinXP & co)
> > as for linux and more modern Windows SHPC hotplug should
> > just work without our ACPI hack (which taxes low memory
> > to keep acpi tables for bridges).
> >
> > So I'm in favor of Michael's suggestion to leave ACPI PCI
> > only in PC machine for old WinXP guests and to keep Q35
> > clean, where linux or newer Windows guests could just
> > use standard SHPC.
> >
> > [...]
>
> I didn't realize windows actually supports SHPC for PCI.

Me neither, if Igor is right I am all for shpc hotplug
since Q35 is not supposed to support older guests.

I remember I succeeded to enable shpc hotplug some time
ago, but only for Linux guests.

Igor, do you have some spec/doc on newer Windows OSes that confirm
PCI shpc hotplug support?

> Do they correctly set _OSC Arg3, bit offset 1?
>         SHPC Native Hot Plug control
>         The OS sets this bit to 1 to request control over PCI/PCI-X Standard 
> Hot-Plug Controller
>         (SHPC) hot plug. If the OS successfully receives control of this 
> feature, it must track and
>         update the status of hot plug slots and handle hot plug events as 
> described in the SHPC
>         Specification.
> I was under impression they only set bit 0.

Alexandr, if modern Windows OSes do support shpc, it makes our
job easier, can you please try to enable shpc hotplug?

Thanks,
Marcel