Subject: Re: Request review of device tree documentation

From: Benjamin Herrenschmidt <[email-masked]>
Date: Sat, 12 Jun 2010 20:48:04 +1000

On Sat, 2010-06-12 at 20:45 +1000, Benjamin Herrenschmidt wrote:
> On Fri, 2010-06-11 at 22:19 -1000, Mitch Bradley wrote:
> > It seems that many of the differences at the CPU level can be determined 
> > by looking at "coprocessor" registers.  For what purpose(s) do we need 
> > to identify the core?  That will inform our choice of a core ID schema.
> 
> The primary thing I see would be architecture version compliance,
> though this is better carried additionally via a binary field in
> the header or a GPR at the entry point, to help the initial asm
> code to setup the MMU etc... before getting into C code.

Also, if you're going to revive a "real" OF port to ARM (with client
interface etc...), should we start considering moving some of powerpc's
prom_init.c to a generic place ?

IE. prom_init is a trampoline that uses the client interface to
essentially create a flatten device-tree and enter the kernel via the
common "epapr" style entry point.

The main drawback is that it doesn't allow to keep OF alive along with
the OS, but then, only sparc does that successfully and I'm not sure
it's something that would be practical to do on ARM either.

Cheers,
Ben.