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Subject: Re: [RFC] PPC: MPIC: necessary readback after EOI?
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Scott Wood <scottwood@freescale.com>
Date: Wed, 07 Jan 2015 15:44:36 +0100
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On Mon, 2015-01-05 at 12:10 -0600, Scott Wood wrote:
> It would have been nice if a code comment explained why it was doing the
> readback...  I don't see any particular need to wait for EOI completion
> here (unlike when masking).

The EOI is what causes the MPIC to drop it's EE output to the CPU, if the
EOI is processed too slowly & asynchronously (posted write + 33Mhz MPIC)
we observe cases of spurrious interrupts. We had some macs basically getting
a spurrious irq for every MPIC interrupts...

Cheers,
Ben.