Re: [Qemu-devel] [PATCH 00/15] qdev: make reset semantics more clear and consistent, reset qbuses under virtio devices

[Peter Maydell]

On 7 January 2013 20:20, Anthony Liguori <address@hidden> wrote:
> Peter Maydell <address@hidden> writes:
>> On 7 January 2013 19:10, Anthony Liguori <address@hidden> wrote:
>>> I think reset really ought to just be a bus level concept with
>>> individual implementations for each bus.
>>
>> I'm not sure I really agree here, especially since QOM/qdev are
>> moving away from the idea that there is a single bus tree and every
>> device is on a single bus.
>
> I don't mean a BusState level concept, I mean a PCIBus concept.
>
> There is clearly such a thing as a PCI bus reset.  In fact, there are
> multiple types of PCI bus resets.  There should be a PCIBus method that
> calls out to PCIDevices on the bus.
>
> But that isn't something that should be fitted into generalized to a
> BusState::reset method.

Ah, I see what you mean now -- yes, definitely.

>> If we want to model reset properly we should model actual reset
>> lines (and/or power-cycling). If we don't care we can continue with
>> whatever fudge we like :-)
>
> Yes, and that's basically what qemu_system_reset() is.  Of course, we
> model it like everything is directly connected to a single power source
> which is true 99% of the time.  That's why we've gotten away with it for
> so long.

I think the bit that's most creaky here is what you do about devices
that want to assert outgoing irq/whatever lines immediately on powerup.

-- PMM