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From: Blue Swirl <blauwirbel@gmail.com>
Date: Sat, 12 Jun 2010 13:44:52 +0000
Message-ID: <AANLkTilFBBEUj30f2E8oyDW3ij5iLUTzfHNBZtb-fOxI@mail.gmail.com>
Subject: Re: [Qemu-devel] [PATCH 09/16] Enable message delivery via IRQs
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To: Paul Brook <paul@codesourcery.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>, Jan Kiszka <jan.kiszka@web.de>, qemu-devel@nongnu.org, Gleb Natapov <gleb@redhat.com>, Juan Quintela <quintela@redhat.com>

On Sat, Jun 12, 2010 at 12:21 PM, Paul Brook <paul@codesourcery.com> wrote:
>> This patch allows to optionally attach a message to an IRQ event. The
>> message can contain a payload reference and a callback that the IRQ
>> handler may invoke to report the delivery result. The former can be used
>> to model message signaling interrupts, the latter to cleanly implement
>> IRQ de-coalescing logics.
>
> I don't like this. qemu_irq is a level triggered interface. Redundant cal=
ls to
> qemu_set_irq should (in principle) be a no-op. =C2=A0If you want message =
passing
> then IMO you should be using something else.

Keeping the optional message and qemu_irq together means that we can
reuse the existing IRQ subsystem. I'd guess something more separated
would need duplicate allocation and delivery support and maybe even
SysBus etc. would need lots of work to support a new class of IRQs.

Also detection of coalesced interrupts depends on reliably detecting
sort of redundant calls to qemu_set_irq. There we don't model real
level triggered hardware exactly but add some extra magic.