7447A strange problem with MSR:POW (WAS: can't boot 2.6.17-rc1)

[Benjamin Herrenschmidt]

On Tue, 2006-04-18 at 15:45 +1000, Paul Mackerras wrote:
> Benjamin Herrenschmidt writes:
> 
> > Looks good to me except that we need the same for ppc64 since the 970
> > theorically has the same problem...
> 
> OK, does this look OK to everyone, before I send it off to Linus?  I
> now use a bit in the thread_info rather than using the HID0 bits
> themselves to indicate that we're napping, since the m[ft]spr might be
> slow.  I added a `local_flags' field to the thread_info struct for
> things that are only changed by the task itself and therefore don't
> need to be accessed atomically.
> 
> This version does the same sort of change for the 970 as for 6xx.

Hrm...

The 970 version bloats the exception prolog significantly... I
understand now why you were talking about putting the code in the exit
path on irc ... I don't like it that way.... Also, if you want to keep
it, maybe use a separate CONFIG_PPC_970STYLE_NAP or something that gets
selected by platforms that can do it ?

I suppose a PACA field would be less inefficient but still sucks... the
exception return to userland code path already accesses thread_info and
definitely looks like a better place to put it... as long as we never
have to add dodgy workarounds when getting out of NAP like we do on 6xx.

Ben.