How do external irq's get mapped?

[Charles Krinke]

-----Original Message-----
From: Sergei Shtylyov [mailto:sshtylyov at ru.mvista.com] 
Sent: Friday, April 27, 2007 10:04 AM
To: Charles Krinke
Cc: Jon Loeliger; Randy Brown; Chris Carlson; Kevin Smith;
linuxppc-embedded at ozlabs.org
Subject: Re: How do external irq's get mapped?

Hello.

Charles Krinke wrote:

> Let me try a more simplified IRQ question a different way by only
> referring to the 8541.

> There are 12 external interrupt sources, irq[0..11] and as I
understand
> it, they all go through one vector, ExternalInput set in
> head_fsl_booke.S and this vector resolves to "do_IRQ()", which I
believe
> is in arch/powerpc/kernel/irq.c (not arch/ppc/kernel/...).

> I am striving to understand how mapping of these external pins
> irq[0..11] gets to IRQ numbers as shown with "cat /proc/interrupts".

    IIUC, the external IRQ #'s should follow those occupied by 32
internal IRQs.
    But those shown in that file are "virtual" numbers, i.e. they got
re-mapped by the kernel as it sees fit (basically, it tries to assign
the same # to IRQs above 15 and remaps those below)

> Could someone point me at some references I can read to understand
this
> nuance of the 8541 in a linux-2.6.17.11 kernel, please.

   I'm not sure arch/powerpc/ in 2.6.17 had the complete MPC8541
support...

WBR, Sergei

So would this mean that the external IRQ0 pin would map to irq #32 and
not irq #16 and the external IRQ11 pin would map to irq #43 and not irq
#27? So that if I want IRQ0, I would set my irq member of the pci_dev
struct to 32?

Charles