Re: [Qemu-devel] [PATCH] Register usb-uhci reset function.

[Paul Brook <paul@codesourcery.com>]

>What about the mantra that we should be as close to HW as possible?
>Reseting state only on a bus level will not work for hot-unplug anyway

Real hardware consists of electrical signals. Qemu emulates the logical 
effects of a device/subsystem, often at a much higher level. Thus "close to HW 
as possible" is no longer a straightforward concept.

Apart from anything else, I'm pretty sure than on all real hotplug PCI systems 
each socket is on its own PCI bus to allow electrical isolation of the device 
before physical hotplug occurs.

> > However having the device explicit set its IRQ line during a full system
> > reset is a different matter. This is probably harmless most of the time,
> > and may paper over other bugs (e.g. the PCI bus not being reset
> > properly). However I do not believe it is the correct justification for
> > these changes.
>
> The IRQ state inside piix3 code is QEMU implementation detail. There is
> now such thing on real HW.

Yes there is. It's a long strip of copper wire with a pullup resistor on the 
end.

Paul