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Subject: Re: [PATCH] [POWERPC] Fix QEIC->MPIC cascading
From: Haiying Wang <Haiying.Wang@freescale.com>
To: Timur Tabi <timur@freescale.com>
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Date: Thu, 20 Sep 2007 15:03:43 -0400
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On Thu, 2007-09-20 at 13:16 -0500, Timur Tabi wrote:
> Anton Vorontsov wrote:
> 
> > I don't know (didn't look) why this works for 83xx w/o ack()...
> > maybe IPIC don't need this. Or maybe there is a bug hiding.
> 
> Scott W told me that me that the IPIC doesn't have the concept of EOI ack.  It 
> just has IRQ masks.

That's true for IPIC, but MPIC has the concept of EOI ack - "An
interrupt is considered in-service from the time its vector is read
(through an IACK cycle) until the end of interrupt (EOI) register is
written. generating what the PIC considers an EOI signal."

On MPC8568, QEIC is a interrupt source of MPIC, so it must send a EOI
signal after the interrupt is served. otherwise, the QEIC interrupt is
always in-service.

Haiying