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Date: Thu, 3 Jun 2010 10:03:01 +0300
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [Qemu-devel] Re: [RFT][PATCH 07/15] qemu_irq: Add IRQ handlers
	with delivery feedback
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To: Jan Kiszka <jan.kiszka@web.de>
Cc: Blue Swirl <blauwirbel@gmail.com>, qemu-devel@nongnu.org, Juan Quintela <quintela@redhat.com>

On Thu, Jun 03, 2010 at 08:59:23AM +0200, Jan Kiszka wrote:
> Gleb Natapov wrote:
> > On Thu, Jun 03, 2010 at 08:23:46AM +0200, Jan Kiszka wrote:
> >> Blue Swirl wrote:
> >>> But how about if we introduced instead a message based IRQ? Then the
> >>> message could specify the originator device, maybe ACK/coalesce/NACK
> >>> callbacks and a bigger payload than just 1 bit of level. I think that
> >>> could achieve the same coalescing effect as what the bidirectional
> >>> IRQ. The payload could be useful for other purposes, for example
> >>> Sparc64 IRQ messages contain three 64 bit words.
> >> If there are more users than just IRQ de-coalescing, this indeed sounds
> >> superior. We could pass objects like this one around:
> >>
> >> struct qemu_irq_msg {
> >> 	void (*delivery_cb)(int result);
> >> 	void *payload;
> >> };
> >>
> >> They would be valid within the scope of the IRQ handlers. Whoever
> >> terminates or actually delivers the IRQ would invoke the callback. And
> >> platforms like sparc64 could evaluate the additional payload pointer in
> >> their irqchips or wherever they need it. IRQ routers on platforms that
> >> make use of these messages would have to replicate them when forwarding
> >> an event.
> >>
> >> OK?
> >>
> > Let me see if I understand you correctly. qemu_set_irq() will get
> > additional parameter qemu_irq_msg and if irq was not coalesced
> > delivery_cb is called, so there is a guaranty that if delivery_cb is
> > called it is done before qemu_set_irq() returns. Correct?
> 
> If the side that triggers an IRQ passes a message object with a non-NULL
> callback, it is supposed to be called unconditionally, passing the
> result of the delivery (delivered, masked, coalesced). And yes, the
> callback will be invoked in the context of the irq handler, so before
> qemu_set_irq (or rather some new qemu_set_irq_msg) returns.
> 
Looks fine to me.

--
			Gleb.