Questions on interrupt vector assignment on MPC8641D

[david.hagood at gmail.com]

> On Tue, 21 Sep 2010 17:37:15 -0400
> The MPIC interrupt numberspace in the device tree (which is not
> virtual; it is a private numberspace to MPIC) is based on the offset of
> the registers for that interrupt source. External interrupts start at
> zero (which is valid), internal at 16, and special things like MSIs at
> higher numbers (I don't think it's quite 256).

OK, so I'm slowly wrapping my head around this (OT: Has anybody considered
sending this information to the folks doing the Linux Device Drivers
books? They are just a bit x86 centric right now...).

As I understand, what I have to do is somehow get a device_node *, then
make a call to irq_of_parse_and_map() to convert that into a system IRQ.

What I am doing right now is:
device_node *mpic = of_find_node_by_type(0,"open-pic");
irq = irq_of_parse_and_map(mpic,256);

While I get a pointer from of_find_node_by_type, when I try to map IRQ
#256 via the irq_of_parse_and_map function, I get a zero back from it.

So I guess my questions would be:
1) should I be frobbing the PIC for this, or should I be looking up some
other device?
2) How do I know for certain that 256 is the right value for the first MSI
signaled via MSIR0?