Subject: Re: [RFC] Device tree for new desktop platform in arch/powerpc

From: Segher Boessenkool <[email-masked]>
Date: Thu, 21 Jun 2007 16:38:49 +0200

>> You probably also want
>> an interrupt-parent property in the isa bridge node pointing back to 
>> the
>> 8259 so it becomes the default for all ISA devices.
> What about PCI devices? Wouldn't it better to define the 
> interrupt-parent property in the PCI bus node?

Devices on an ISA bus have their interrupts encoded according
to the ISA bus binding; this is exactly the format that the
ISA interrupt controller (the 8259) expects, so by setting
the interrupt-parent on the bus node to point to the 8259 (and
not doing interrupt mapping in the ISA child nodes) all works
exactly as planned.

Devices on a PCI bus have their interrupts encoded according
to the PCI bus binding; this is a very much different format
so you better have a real mapping (probably in the PCI host
bridge) translating it to ISA interrupts (and pointing it there),
if that's how the interrupts are routed on your box.

I hope this helps, it's a bit hard to explain without whiteboard :-)

Segher