Re: [Qemu-devel] [PATCH 1/7] Introduce a new bus "ICC" to connect APIC

[Anthony Liguori <anthony@codemonkey.ws>]

On 02/24/2012 07:40 AM, Paolo Bonzini wrote:
> On 02/24/2012 02:30 PM, Andreas Färber wrote:
>> SysBus is supposed to go away in Anthony's upcoming 4th QOM series, so
>> I'd rather not base a new series on that.
>
> Not sure about that.  I haven't understood well the scope of the series,
> but I think it only converted buses to QOM, it didn't kill them.
> Perhaps SysBus was special, in which case it would become automatically
> hotpluggable: just create a new QOM object.
>
>> The issue with TYPE_DEVICE is that we don't want to leak that into the
>> user emulators (would break the build), and any infrastructure only
>> available to qdev should gradually be made accessible to all objects
>> (Paolo has done some work in that direction wrt properties).
>
> I haven't, but it would be next on the list of things to do.
>
>> So the main remaining difference between Object and Device is the
>> GPIO IRQ support. Anthony wanted to introduce Pin objects to replace
>> qemu_irq.
>
> Aiming at "replacing" is a bad idea unless you can do it fast and
> painlessly.  Adding gpio_in and gpio_out property types would be more
> useful and would let you expose qemu_irq as QOM.

I agree with you in principle, but in practice, there is not obvious way to 
serialize gpio_in/gpio_out via Visitors.  Finding some way to do it as an 
integer is clearly wrong IMHO.

I think a simple Pin object with the following interfaces:

/**
  * Connect a pin to a qemu_irq such that whenever the pin is
  * raised, qemu_irq_raise() is called too on irq.
  */
void pin_connect_qemu_irq(Pin *obj, qemu_irq irq);

/**
  * Returns a qemu_irq such that whenever qemu_irq_raise() is
  * called, pin_set_level(obj, true) is called.
  */
qemu_irq pin_get_qemu_irq(Pin *obj);

Let's you incrementally refactor objects to use Pins while maintaining the 
existing qemu_irq infrastructure.

Regards,

Anthony Liguori

>  You can then change
> the existing qdev.c functions to operate on those new property types.
>
> Paolo