Re: [Qemu-devel] [PATCH v2] sysbus: add irq_routing_notifier

[Eric Auger]

On 04/27/2015 04:39 PM, Peter Crosthwaite wrote:
> On Mon, Apr 27, 2015 at 6:37 AM, Paolo Bonzini <address@hidden> wrote:
>>
>>
>> On 27/04/2015 14:20, Eric Auger wrote:
>>> On 04/27/2015 12:39 PM, Paolo Bonzini wrote:
>>>>
>>>>
>>>> On 27/04/2015 10:26, Eric Auger wrote:
>>>>>>> One of my long term goals is to try and get rid of sysbus IRQ
>>>>>>> abstraction completely in favor of just qdev gpios. This means
>>>>>>> features that apply to GPIOs automatically apply to IRQs and vice
>>>>>>> versa. Can your notifier hook be pushed up to the qdev GPIO level to
>>>>>>> make it more globally usable and avoid a new feature to sysbus IRQs?
>>>>> Yes sure, I am going to put the notifier in DeviceClass then.
>>>>
>>>> I've thought too about this, and I'm not sure about it.
>>>>
>>>> It would mean you have to pass the gpio name (e.g.
>>>> SYSBUS_DEVICE_GPIO_IRQ) to the hook, and in the case of sysbus IRQs this
>>>> would leak the SYSBUS_DEVICE_GPIO_IRQ abstraction to the implementors of
>>>> the hook.
> 
> That's OK IMO. SYSBUS_DEVICE_GPIO_IRQ was never intended to be
> private. The semantics of it are something like "If you don't have
> anything better to name your IRQ pin use this".
> 
> This adds the requirement on machine level code that you can't
> consistently use sysbus_connect_irq for intc connection. But machines
> should be able to connect any wires between any cores without having
> to special case interrupts or chip-selects, resets or whatever. So the
> name of the GPIO has to be exposed to the callback hook registration
> if we want to break down this GPIO special casing. Names of interrupt
> pins are system-level knowledge so I think this is all OK.
> 
>>> Hi Paolo,
>>>
>>> Currently my notifier has the following proto:
>>>     void (*connect_gpio_out_notifier)(DeviceState *dev, qemu_irq irq);
>>>
>>> It is sufficient for my need.
>>>
>>> is it really mandated to pass other qdev_connect_gpio_out_named args,
>>> ie. name & n?
>>
>> It's an ugly situation.  If you look at qdev_connect_gpio_out_named, it
>> is really a thin wrapper around object_property_set_link.  Just like
>> Peter wasn't too happy with changing sysbus_connect_irq, the same
>> objection would apply here.  Callers of object_property_set_link should
>> call the notifiers, not just those that use qdev_connect_gpio_out_named.
>>
>> This is why I originally asked you to look into using the check callback
>> instead.
>>
> 
> Is this still feasible? Pushing it up to the higher again to the QOM
> level? I think this would be an ideal backend to the problem even if
> we still go with a code-friendly sysbus frontend.

Peter, Paolo,

After your feedbacks, I feel I need to spend some more time on the
original check() track. I would prefer not to introduce any patch that
will make issue in the future.

Thanks

Eric

> 
> Regards,
> Peter
> 
>> This is why I think it's better to keep the sysbus patch.
>>
>> Paolo
>>