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

[Paul Brook <paul@codesourcery.com>]

>> If allow devices to be reset independently then they should probably set
>> theit IRQ output on reset.
>
>It is not "if" it is "when". We have to allow device to be reset
> independently for hot-unplug.

I'm not entirely convinced about reset-on-hotunplug. What about a device that 
pulls its IRQ line high on reset?

> > The only relevant circumstances are if the devices raises an IRQ, and is
> > then reset by software while the system is running. It's got nothing to
> > do with piix3, PCI bus interrupt sharing or system reset. If you are
> > seeing problems after a system reset then your bug lies elsewhere.
>
> So you apparently never heard about hardware reset? You never saw buggy
> guests that does not reset HW before reboot?

Clearing device state on full system reset makes sense because the whole point 
is that we're returning the system to its power-on state.
Lowering the IRQ when a single device is reset also makes sense.

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.

Paul