Re: [Qemu-devel] [PATCH] pc: Clean up PIC-to-APIC IRQ path

[Avi Kivity]

On 09/05/2011 11:38 AM, Edgar E. Iglesias wrote:
> >
> >  We shouldn't really use the term IRQ as it's confusing.  I like the term
> >  "pin" better because that describes what we're really talking about.
> >
> >  qemu_irq is designed oddly today because is represents something that is
> >  intrinsically state (whether a pin is high or low) with an edge
> >  notification with the assumption that the state is held somewhere else
> >  (which is usually true).
>
> I don't agree. That's not what qemu_irq represents.
> It represents a wire, a mechanism to drive changes through logic paths
> between state. It is intrinsically stateless.
>
> It may be the case that it is missused in some places, or that it isn't
> always the best thing to use to represent what ever you need to represent,
> so that you want to complement with other mechanisms.
> But universally replacing it with a stateful alternative seems wrong to me.

I agree that qemu_irq is inherently stateless.  But I do think there 
should be a way for the sink to query the line level.  Whether it is 
implemented as a cache of the last qemu_set() level, or with callbacks 
that query the underlying state is not important, but we can't just rely 
on edge triggers.

(real hardware can query a line at any time, yes?)

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