Re: [v2 1/1] hw/i386/acpi-build: add OSHP method support for SHPC driver load

[Igor Mammedov]

On Mon, 1 Jul 2024 14:27:50 +0000
"Gao,Shiyuan" <gaoshiyuan@baidu.com> wrote:

> > > > > If I want to use ACPI PCI hotplug in the pxb bridge, what else need 
> > > > > to be done?  
> > > >
> > > > does it have to be hotplug directly into pxb or
> > > > would be it be sufficient to have hotplug support
> > > > on pci-bridge attached to a pxb?  
> > >
> > > It's sufficient to hotplug support on pci-bridge attached to a pxb.  
> >
> > ... but I guess using this instead would be better anyway?  
> 
> https://lore.kernel.org/all/20220422135101.65796823@redhat.com/t/#r831d589f243c24334a09995620b74408847a87a0
> 
> According this message, It seems that the current QEMU does not support it 
> yet. 
> I tried to hotplug on pci-bridge attached to a pxb, no device found in the 
> guest.

SHPC works for q35, which provides _OSC.

It is broken for pc machine though, since machine lacks either _OSC or OSHP.
Theoretically SHPC should still work for hotplugged bridges
(i.e. with ACPI hotplug enabled, when one hotplugs a bridge into
pci.0, but I haven't tried that lately)

I'm still not sure if we should make OSHP global, or put it only
under bridges that have shcp=on && don't have ACPI hotplug.
The later seems cleaner though.

> >
> > take care,
> >   Gerd  
>