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Date: Mon, 16 Jul 2007 17:18:52 -0500
From: Scott Wood <scottwood@freescale.com>
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To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [RFC][PATCH 6/8] Walnut DTS
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Cc: linuxppc-dev@ozlabs.org, Yoder Stuart-B08248 <stuart.yoder@freescale.com>
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Benjamin Herrenschmidt wrote:
> No, interrupt maps are useful in devices with no children in some corner
> cases. Remember that a map doesnt need to use the address part of the
> source specifier, thus it can be used to do a pure domain->domain
> conversion of the irq numbers, what sort of thing. The map has the added
> advantage that today, it's the only mechanism that allows you to specify
> different interrupt-parents through the same nexus, which is useful for
> 4xx.

OK...  but if you're doing a pure IRQ number conversion, the only useful 
#address-cells would be zero, which makes it a reasonable default IMHO 
(unlike the arbitrary 2 for regular traversal).

-Scott