[Qemu-devel] Re: qdev: Some ISA devices don't handle second instantiation gracefully

[Gerd Hoffmann <kraxel@redhat.com>]

   Hi,

>> They call register_ioport_write(), which aborts via hw_error() when
>> the port is already in use.  This is okay for non-configurable
>> parts of a board emulation, but not okay for a qdev device, unless
>> it has no_user set.
>>
>> Related: when isa_init_irq() finds the requested IRQ already in
>> use, it fails with exit(1).  Maybe register_ioport_write()&
>> friends should do that as well.
>>
>> Or maybe qdev device models should have an "at most one" flag.
>
> There can be multiple of these devices on different ports, but a
> single PIO port can still only be managed by a single device. By
> creating the same device twice without giving it a PIO option, you
> put two devices on the same PIO port which can't work.
>
> As this is a configuration error, I'd guess the best way to deal with
> it is to return an error for register_ioport which makes the qdev
> init fail. Then the respective instantiator can do what is fit. If
> the device is passed in on the cmdline, it'd refuse to create the
> machine and exit. If it's a hotplug event, it would fail to hotplug.

ISA isn't hotpluggable anyway, so just exiting unconditionally here 
isn't a big issue IMHO as effectively only ISA devices are affected by 
this.

register_ioport_write() should exit with a more useful error message 
here instead of calling hw_error() though.

We could also make register_ioport_write() pass up an error and have all 
callers check that.  Not sure this is worth the trouble though.

An "at most one" flag might make sense.  But on a PC all ISA devices 
which exist only once at a fixed address (keyboard, floppy, ...) are 
automagically created so no_user does the trick here.  The other ones 
(serial, ne2k_isa, ...) actually can be created multiple times if you 
configure different iobases using properties.

Dunno what kind of device apple-smc is ...

cheers,
   Gerd