[PATCH v3 4/4] powerpc/64s: idle ESL=0 stop can avoid MSR and save/restore overhead

[Nicholas Piggin]

On Wed, 30 Aug 2017 21:25:59 +1000
Michael Ellerman <mpe at ellerman.id.au> wrote:

> Nicholas Piggin <npiggin at gmail.com> writes:
> 
> > When stop is executed with EC=ESL=0, it appears to execute like a
> > normal instruction (resuming from NIP when woken by interrupt).
> > So all the save/restore handling can be avoided completely. In
> > particular NV GPRs do not have to be saved, and MSR does not have
> > to be switched back to kernel MSR.
> >
> > So move the test for "lite" sleep states out to power9_idle_stop.
> >
> > Reviewed-by: Gautham R. Shenoy <ego at linux.vnet.ibm.com>
> > Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> > ---
> >  arch/powerpc/kernel/idle_book3s.S | 35 ++++++++++++++++++++++++-----------
> >  1 file changed, 24 insertions(+), 11 deletions(-)  
> 
> This is blowing up for me on mambo:

Oh this is a known bug in mambo that does not match the hardware.

You need >= Mambo.7.8.21, or this firmware patch to work around
the issue for old mambos.

mambo.git 58d3162f4d6204fc077ff4a6ba47e4d1e19d5120

https://lists.ozlabs.org/pipermail/skiboot/2017-August/008768.html

Thanks,
Nick