From mboxrd@z Thu Jan  1 00:00:00 1970
From: tglx@linutronix.de (Thomas Gleixner)
Date: Wed, 2 Mar 2011 18:10:20 +0100 (CET)
Subject: [PATCH 6/6] ARM: nmk: update GPIO chained IRQ handler to use
	EOI in parent chip
In-Reply-To: <001301cbd8ef$29403c10$7bc0b430$@deacon@arm.com>
References: <1298900022-21516-1-git-send-email-will.deacon@arm.com>
	<1298900022-21516-7-git-send-email-will.deacon@arm.com>
	<20110228140327.GA1937@n2100.arm.linux.org.uk>
	<001401cbd772$a1f93ae0$e5ebb0a0$@deacon@arm.com>
	<alpine.LFD.2.00.1102281949050.2701@localhost6.localdomain6>
	<20110228214445.GD1937@n2100.arm.linux.org.uk>
	<alpine.LFD.2.00.1103011140560.2701@localhost6.localdomain6>
	<20110301201904.GA27107@n2100.arm.linux.org.uk>
	<alpine.LFD.2.00.1103012133530.2701@localhost6.localdomain6>
	<001301cbd8ef$29403c10$7bc0b430$@deacon@arm.com>
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To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Wed, 2 Mar 2011, Will Deacon wrote:

> Hi Thomas,
> 
> > Can you please take the time and explain me the difference of the
> > following:
> > 
> > irqchip1.c
> > 
> > struct irq_chip1;
> > 
> > handle_primary_irq(int irq, struct irq_desc *desc)
> > {
> > 	chip->irq_ack();
> > 	desc->demux();
> > }
> > 
> > init()
> > {
> > 	irq_set_chip(PRIMARY_IRQ, &irq_chip1);
> > 	irq_set_primary_handler(PRIMARY_IRQ, handle_primary_irq);
> > }
> 
> I think with this approach you get the exact opposite problem; that
> is the primary irq_chip doesn't know which IRQs are going to be
> demuxed so it cannot know at init time which IRQs need their primary 
> handler set. Is the idea that you set_primary_handler for all IRQs,
> stash that in the descriptor somewhere and then replace handle_irq
> with the primary handler when a demux handler is registered?
> 
> I guess I'm missing something here,

No, I missed that. Darn, yes this would need storing the
primary_handler in some separate pointer or having a callback into the
chip implementation to make this fully distangled.

Grmbl.

	tglx