Subject: Re: [PATCH 2/5] powerpc: Generic device tree for all AmigaOne boards

From: Benjamin Herrenschmidt <[email-masked]>
Date: Mon, 12 Jan 2009 16:12:18 +1100

> Yes, all AmigaOne boards have physical PCI slots (at least 1). The different
> interrupt routing wasn't a problem so far, as the firmware writes the IRQ number
> to the interrupt line register of every PCI device.

The code in the kernel that retreives the interrupt that way is clearly
marked as a fishy workaround for bogus firmwares :-)

But I'm not going to reject things based on that, it will work for
simple board using really only legacy interrupts like yours...

> Currently the kernel reads the IRQ number from this register, if there is no
> interrupt mapping property. I know that it's not a good idea to rely on kernel
> fallback behavior, but it makes a lot of things easier in this case.

Sort-of. As long as it's really 8259 interrupts, I suppose it's
acceptable.

> > For the flattened device tree, I think we've settled on the convention
> > that every node with an IRQ connection should have both the
> > interrupt-parent and interrupts properties.  (ie. don't rely on the
> > parent node's interrupt-parent property.)
> Even for ISA devices?

I disagree with Grant here. Especially in simple ISA cases like that,
there's really no point in bloating the device-tree.

> > Can this PCI device be probed?  Typically PCI devices don't get added
> > to the flattened device tree because PCI is a probeable bus.
> Yes, it can be probed. I thought it would be a good idea to include it,
> because the IDE controller operates in legacy mode. I planned to specify the
> two legacy interrupts in this node (as you can see), but the kernel didn't like
> them.

Well, the kernel just didn't make use of them I'd say :-) But that can
probably be fixed with the appropriate hacks. 

Cheers,
Ben.