[RFC PATCH 04/19] powerpc: wii: device tree

[Segher Boessenkool]

>> There you can find the hardware interface that supports the IPC  
>> mechanism.
>> It is made up of a pair of registers to pass data between the  
>> processors and a
>> pair of control/flags registers.
>> The hardware can interrupt the PowerPC side when there is data  
>> available for it.
>
> Ok. So the right way to do that would be to have a node purely
> representing the HW IPC, unrelated to whatever is running on the
> secondary processor.

Or you can keep it implicit in the Hollywood control registers.
It is one 512-byte block with lots of things thrown together (and
then mixed up real good).

> However, it's ok to have -below- that node, a set of device nodes or a
> node with properties or whatever representing the FW in there and the
> function it exposes.

That's not really useful though, it's easy to probe for.

> What might do however is to have a way for that FW itself to  
> provide you
> with the nodes and properties for the functions it provides :-)

You get a pointer at the very last word of memory.  It point to an
info header that has everything you need to know (most importantly,
a version identifier).

> Of course that wouldn't work with FW we don't have control on. Can  
> Linux
> run on the wii with the original N. FW on the aux. processor ?

It _can_, but there are no advantages to doing that, and lots and  
lots of
disadvantages, so the plan is to not add support for that in mainline.

> Can we
> detect what is running there ? Do we care ?

You can detect this for anything that uses a mini-compatible interface.
You shouldn't care for anything else ;-)


Segher