Kernel Regression: Wallstreet (was Re: OldWorld ROM Macintoshes)

The only kernel where I'm seeing a system hang on the Wallsteet 
(framebuffer console blank, backlight on, system doesn't boot) is 
vmlinux-6.6.3+deb14-powerpc. I don't see that failure with any of the 
mainline kernels that I checked.

With mainline kernels, I see two failure modes:

1) The framebuffer console freezes at the BootX screen in Mac OS, but 
Linux still boots and the system can be accessed over the network.
2) X11 initiation fails, but the system reaches a text login at the 
framebuffer console.

There appears to be a kernel regression between v6.2-rc1 and v6.2-rc8:

v6.2-rc1  : X11 works
v6.2-rc8  : failure mode 1

There may be a second issue (or perhaps a fix of failure mode 1 that 
triggered failure mode 2) between v6.4-rc1 and v6.4-rc7:

v6.4-rc1  : failure mode 1
v6.4-rc7  : failure mode 2

I'll send another update in a few days after doing a kernel bisect.

-----

v5.18     : X11 works
v6.1      : X11 works
v6.2-rc1  : X11 works
v6.2-rc8  : failure mode 1
v6.2      : failure mode 1
v6.4-rc1  : failure mode 1
v6.4-rc7  : failure mode 2
v6.4      : failure mode 2
v6.6      : failure mode 2
v6.16     : failure mode 2
v6.17-rc4 : failure mode 2