Booting OS on PowerPC

[Paul Mackerras]

Segher Boessenkool writes:

> Perhaps I should apologize for making it sound like his answer
> was fully incorrect; that was unintended, I meant more something
> like "incomplete".
> 
> Anyway...  The question didn't say PAPR, it even said PowerPC :-)
> But I just checked, and the PAPR also doesn't require GPR3 and
> GPR4 to be zero.

It does, in section C.10.2.

Anyway, I was just trying to clarify which domain Milton's answer
related to, and that it was correct for that domain.

Part of the confusion comes from the fact that we don't have a single
transfer of control (i.e. from OF to the kernel); we have at least two
(OF -> yaboot -> kernel or OF -> zImage -> kernel) and possibly three
(OF -> yaboot -> zImage -> kernel), and slightly different conventions
can apply at each transfer.

> I also checked the kernel (the converged arch/powerpc one); GPR6
> and GPR7 are unused.  GPR3 and GPR4 are used for passing an initrd,
> which is used by yaboot (at least by my ancient 1.3.12 copy).  This
> mechanism is a bit fragile (relying on GPR4 never to be 0xdeadbeef
> when GPR3 and GPR4 are not an initrd; and the real vs. virtual hack);
> perhaps yaboot should set the linux,initrd-* properties in /chosen
> itself?

That would be a good idea.

Paul.