Re: [Qemu-devel] [PATCH RFC 0/3] basic support for composing sysbus devices

[Anthony Liguori]

On 06/10/2011 08:50 AM, Peter Maydell wrote:
> On 10 June 2011 14:43, Jan Kiszka<address@hidden>  wrote:
> > On 2011-06-10 15:10, Peter Maydell wrote:
> > > This makes the wiring of this signal look like a property of the
> > > isa-serial device, which is a bit odd, since it's just as much
> > > a property of the piix3. Actually it's neither, it's a property
> > > of the machine model, and you might actually want a syntax a bit
> > > more like:
> > >
> > >   piix3 = piix3(property=value, property=value...);
> > >   serial = isa-serial(property=value...);
> > >   connect(serial.irq, piix3.irq[3]);
> >
> > In fact, in the ISA case, it is a device property: The device, and only
> > the device decides which IRQ to use - from the bus it is attached to. So
> > attaching an ISA device to the bus of an ISA bridge like the PIIX3 and
> > selecting local IRQ 3 are the steps we can already express today.
>
> Ah, in that case Anthony's suggestion of
>    -device piix3,id=piix3 -device isa-serial,id=serial,irq=piix3.irq[3]
> wrong in a different way -- the isa-serial shouldn't care
> what other device is providing the ISA bus it is sitting on,

If it really makes you feel bad, you could also do:

 -device piix3,id=piix3
 -device wire,id=wire,in=piix3.irq[3]
 -device isa-serial,id=serial,irq=wire.out

Regards,

Anthony Liguori

> it just has a property of which ISA irq line it is using
> (and rely on an isa bus abstraction to wire things up at
> the machine model level). [As you say, this works now.]
>
> But I think that's a non-typical case compared to the usual one
> of "these wires are just hardwired this way by the machine".
>
> -- PMM