Date: Fri, 4 Jul 2008 09:08:03 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: michael@ellerman.id.au
Cc: benh@kernel.crashing.org, Matthew Wilcox <matthew@wil.cx>,
       Arnd Bergmann <arnd@arndb.de>, linux-pci@vger.kernel.org,
       Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>,
       Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
       David Miller <davem@davemloft.net>,
       Dan Williams <dan.j.williams@intel.com>, Martine.Silbermann@hp.com,
       linux-kernel@vger.kernel.org
Subject: Re: Multiple MSI
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> In most cases that I can see the conversion from irq number to irq_desc
> is done in the genirq code, so I don't see why you couldn't just put a
> remapping in there from irq numbers to descs that doesn't use an array. 
> But maybe I'm missing something.

There are a pile of drivers you would also need to fix up that use NR_IRQ
sized tables. There is also the performance concern. The irq->desc
conversion has to be very fast.

It would be better (IMHO) if dev->irq and irq in general was a pointer
whose number for end users was irq->num or similar.
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