[Skiboot] [RFC PATCH] Use two VSX registers to do initial copy of skiboot

[Stewart Smith]

Benjamin Herrenschmidt <benh at kernel.crashing.org> writes:
>> benh, can we use the ipl-params/ipl-params/cec-major-type property to
>> mark "cold" boots as having zeroed memory, and hence skip some of these?
>> I'd like to do this at run time, rather than compile time .
>
> I don't know whether we have any guarantee from hostboot that we have
> zeroed memory. In fact we don't ... HB itself has left remains behind.

Hrm... that's true.

> We'll need a specific type to represent a sim env. with initial zeroed
> memory.
>
> Another bunch of things to consider:
>
>  - Remove useless clearing unconditionally. For example, stacks. We only
> need to clear the cpu_thread structure at the bottom and the last
> backlink.

May be useful to (like mem poisoning) poison the stacks on boot too, may
find something exciting and annoying to debug!

>  - Make clearing more efficient. Stewart gave it a good try but what
> about using dcbz ?

yeah, that's probably what we should end up doing. I was just looking
into the implementation that ended up in linux, I'm tempted to try
something with dcbz, yeah. Or, even better, I go to the pub early and
Mikey does it and sends me patches :)

>  - Link skiboot at 0x3000_0000 so when pre-loaded there, it doesn't need
> to relocate itself (skip not just copy but also relocation phase).

That could be useful, yeah.