Re: [Qemu-devel] [PATCH 16/27] acpi: ich9: allow guest to clear SCI rised by GPE

[Li Guang]

Michael S. Tsirkin wrote:
> On Thu, Nov 21, 2013 at 04:32:27PM +0800, Li Guang wrote:
>    
> > Michael S. Tsirkin wrote:
> >      
> > > On Thu, Nov 21, 2013 at 04:18:45PM +0800, Li Guang wrote:
> > >        
> > > > Hu Tao wrote:
> > > >          
> > > > > On Thu, Nov 21, 2013 at 09:14:18AM +0200, Michael S. Tsirkin wrote:
> > > > >            
> > > > > > On Thu, Nov 21, 2013 at 03:38:37AM +0100, Igor Mammedov wrote:
> > > > > >              
> > > > > > > it fixes IRQ storm since guest isn't able to lower SCI IRQ
> > > > > > > after it has been handled when it clears GPE event.
> > > > > > >
> > > > > > > Signed-off-by: Igor Mammedov<address@hidden>
> > > > > > >                
> > > > > > The storm is only on memory hotplug right?
> > > > > >              
> > > > > IIRC, it happens on cpu hotplug, too.
> > > > >
> > > > >
> > > > >
> > > > >            
> > > > :-), that made remember EC implementation,
> > > > with EC, SCI will be safer, I think.
> > > >          
> > > Hmm you are saying let's use EC for memory hotplug?
> > >
> > >
> > >        
> > It can be a bridge between guest and QEMU,
> > with it, we may don't have to bother ASL writing
> > and south-bridge hardware related work(or very
> > little) if we implement EC correctly.
> >
> >
> >      
>
> I'd like to see that. Can you write a document (just text)
> for an imaginary EC support for memory hotplug?
>
>
>
>    

Hmm..., with EC,

For memory hotplug, at least,
ASL at [PATCH 27/27] can be replaced
by a simple Method(_Qx) under EC device,
IO base operations at [PATCH 15/27]
are dispensable,  we can relay data
by standard operations of EC space

and also for SCI, all device changes want to
notify guest OS can share same SCI with EC,
and the operations are specified at ACPI SPEC.

likewise, for CPU hotplug, pvpanic,
and even debugcon.

and, for odd devices, like pvpanic, guest OS may complain
about it, and we may also have to bother on maintaining state of
it at QEMU, and writing a driver for guest OS,
with EC, functions of device like pvpanic may be implemented silently,
and EC is ACPI standard device, each ACPI compatible OS will
have a driver for it natively.