How do external irq's get mapped?

[Jon Loeliger]

On Fri, 2007-04-27 at 12:03, Sergei Shtylyov wrote:
> 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)

And remember, Ben distorted the IRQ World right about
somewhere in that time frame too.

Kumar, can you remind us?

> > 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...

Which might be a different way of saying "You should try the
current top of git or 2.6.21." :-)

jdl