Rob Landley writes:

Just to correct a few misconceptions:

2) PowerPC uses a device tree supplied by the hardware to identify the 
available hardware, even for stuff living on PCI busses which it could 
theoretically probe for but doesn't.

The device tree doesn't have to include anything that can be probed
for.  On some platforms (e.g. pSeries) we choose to use the device
tree rather than probing, but on most other platforms we probe.

I'd be following this more closely if compiling a device tree didn't currently 
require an external utility (dtc or some such) that doesn't come with the 
Linux kernel.  No other target platform I've built kernels for requires such 
an environmental dependency.

No?  You haven't built kernels for other platforms that have external
dependencies such as perl, gcc, make, binutils, etc.? :)

 (This is a problem both for hardwiring the 
device tree into the kernel and for building a new boot rom from the linux 
kernel's ppc boot wrapper that would contain such a device tree to feed to 
the kernel.)

It's only really been a problem for ps3 so far, since the embedded
guys don't seem to have any difficulty with installing dtc.  We are
looking at what to do for ps3 and prep, and the answer may well
involve bundling dtc in the kernel source (it's not too big, around
3400 lines).

Paul.