[Skiboot] [RFC 1/1] OPAL : Support spr save-restore using new opal call

[Nicholas Piggin]

On Fri, 20 Jul 2018 16:30:51 +0530
Abhishek Goel <huntbag at linux.vnet.ibm.com> wrote:

> In an attempt to make the powernv idle code backward compatible,
> and to some extent forward compatible, add support for pre-stop entry
> and post-stop exit actions in OPAL. If a kernel knows about this
> opal call, then just a firmware supporting newer hardware is required,
> instead of waiting for kernel updates.
> This opal support for stop can be indicated by a compatibility string
> in the newly proposed device-tree format (Ref:
> https://patchwork.ozlabs.org/patch/923120/). Thus the kernel can
> enable a stop state, when the opal support for it exists, even if the
> kernel support doesn't exist.

I'm hoping rather than a save API it should just be an enter-idle
call, and it would expect another call in response to a powersave
wakeup (or it could return in the case of EC=0 type idle).

The problem is we may need a new special OPAL call API for
the wakeup case because that would be re-entrant. IMO we also
need something similar for OPAL machine check handling, so we
should think about it and see if something can fit both.

I'd like Linux not to have to know about any saving of core
vs thread SPRs or even PSSCR or STOP meanings. Just use an
idle state number it got from dt.

Thanks,
Nick