Mac Mini G4 hang on boot with git master

[Mark Cave-Ayland]

On 15/03/2019 13:37, Mark Cave-Ayland wrote:

> Hi all,
> 
> I've just done a git pull and rebuilt master on my Mac Mini G4 in order to test
> Michael's merge of my KVM PR fix, and unfortunately my kernel now hangs on boot :(
> 
> My last working git checkout was somewhere around the 5.0-rc stage, so I suspect it's
> something that's been merged for 5.1.
> 
> The hang occurs just after the boot console is disabled which makes me wonder if
> something is going wrong during PCI bus enumeration. Does anyone have an idea as to
> what may be causing this? I can obviously bisect it down, but on slow hardware it can
> take some time...

This was a weird one: bisecting directly from git master gave a nonsense result,
however by manually rebasing Michael's PR onto my last known good commit from master
I was able to finally pin it down to this commit:


7a0d6955f3f7a4250da63d528bfff7a9c91b5725 is the first bad commit
commit 7a0d6955f3f7a4250da63d528bfff7a9c91b5725
Author: Christophe Leroy <christophe.leroy at c-s.fr>
Date:   Thu Feb 21 10:37:55 2019 +0000

    powerpc/6xx: Store PGDIR physical address in a SPRG

    Use SPRN_SPRG2 to store the current thread PGDIR and
    avoid reading thread_struct.pgdir at every TLB miss.

    Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>
    Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>


ATB,

Mark.