[PATCH] powerpc/64s: power4 nap fixup in C

[Nicholas Piggin]

Excerpts from Andreas Schwab's message of March 30, 2021 2:23 am:
> On Mär 29 2021, Andreas Schwab wrote:
> 
>> On Mär 29 2021, Michael Ellerman wrote:
>>
>>> Nicholas Piggin <npiggin at gmail.com> writes:
>>>> There is no need for this to be in asm, use the new intrrupt entry wrapper.
>>>>
>>>> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
>>>> ---
>>>> Hopefully this works on a real G5 now, but I couldn't reproduce the
>>>> problem with QEMU.
>>>
>>> It still prevents my G5 from booting.
>>
>> I see differing failures.  What's common is that there is a pause of
>> about 60 seconds before the crash occurs.  It looks like the crash
>> occurs in power4_idle_nap+0x30/0x34.  Unfortuately, the BootX console is
>> too small to see enough.
> 
> I was now able to see the messages on the VGA console, and the problem
> is actually that the cpus are starting to stall.

This is strange, I haven't been able to figure out what is wrong.

I've been looking at QEMU code and now I'll have to try find a POWER4/5
or PPC970 manual to see what exactly this MSR[POW] thing does and make 
sure QEMU matches it.

Progress might be slow. Worst case I guess we revert if it can't
be fixed before next merge window.

Thanks,
Nick