Found the commit for: 5.3.7 64-bits kernel doesn't boot on G5 Quad

[Romain Dolbeau]

Le dim. 10 nov. 2019 à 11:45, Romain Dolbeau <romain at dolbeau.org> a écrit :
> Any suggestion, advice, or patch to try welcome :-)

>From my bisect, I figured that
0034d395f89d9c092bb15adbabdca5283e258b41 was the likely culprit, but
that the bug was masked by the printk() issues that were fixed later:
commit 2ac5a3bf7042a1c4abbcce1b6f0ec61e5d3786c2 mentions "Report on
Power: Kernel crashes very early during boot". Once that was merged,
the current bug appears instead of the early crash.

So what I did was:

1) checkout 0034d395f89d9c092bb15adbabdca5283e258b41
2) merge printk-for-5.2 & printk-for-5.2-fixes from pmladek/printk,
hoping to remove the printk issue ; there was only fairly trivial
conflicts

-> the resulting kernel displays the same bug as Debian's and vanilla
5.3 and HEAD, which is what I hoped for.

However, the merges did pick up quite a few commits, so I then:

3) did a revert of only 0034d395f89d9c092bb15adbabdca5283e258b41 ;
that did not cause conflicts (on HEAD, this causes a lot of conflicts
I don't know how to resolve).

-> the resulting kernel works fine ! :-)

So it seems to me that 0034d395f89d9c092bb15adbabdca5283e258b41
introduced the bug that crashes the PowerMac G5 (as/could anyone
tried/try on some other PPC970-based system, like a JS20 ? to see if
it's PowerMac-specific or not).

If anyone has an idea on how to fix this, that would be very welcome,
as I'm way out of my depth in the PPC64 MMU code.

Cordially,

-- 
Romain Dolbeau