G5 Quad hangs early on 4.20.2 / 5.0-rc2+

[Benjamin Herrenschmidt]

On Tue, 2019-01-15 at 23:49 +0100, Tobias Ulmer wrote:
> Hi,
> 
> both the latest stable 4.20.2 and 5.0 rc2+ hang early on the G5 Quad.
> 
> Surely I'm not the first to run into this, but I couldn't find any
> discussion or bug report. Sorry if you're already aware.
> 
> You can see it hang here (5.0 rc2+, 4.20.2 is nearly identical) until
> the watchdog triggers a reboot:
> 
> https://i.imgur.com/UiCVRuG.jpg
> 
> If I had to make an uneducated guess, it seems to boot into the same
> codepath twice (mpic was already initialized, then it starts again right
> after smp bringup). Maybe on a second CPU?
> 
> To narrow it down a little, my last known good was 4.18.9

I don't think it's an MPIC related problem but it does appear to hang
about when interrupts get turned on.

I have one of these critters in the office, but I'm working remotely
this week so I won't be able to dig into this until next week.

It might help if you could bisect in the meantime.

Cheers,
Ben.