I bisected today.

1. git clone https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git -b powerpc-6.19-1 a

2. cd a

3. git log

Output:

commit 9b36c7fc5aa5f2c6e6eeb9f312fdfe61b4291c9f (HEAD, tag: powerpc-6.19-1, origin/next-test, origin/next)

...

4. git bisect start

5. git bisect good f850568efe3a7a9ec4df357cfad1f997f0058924

Merge tag 'i2c-for-6.18-rc5'

6. git bisect bad 9b36c7fc5aa5f2c6e6eeb9f312fdfe61b4291c9f

macintosh/via-pmu-backlight: Include <linux/fb.h> and <linux/of.h>

7. git bisect bad

8. git bisect bad

9. git bisect good

10. git bisect bad

11. git bisect good

2997876c4a1a5864baa13d7393c2b68cf5b51183 is the first bad commit
commit 2997876c4a1a5864baa13d7393c2b68cf5b51183
Author: Christophe Leroy [off-list ref]
Date:   Thu Sep 11 14:30:12 2025 +0200

    powerpc/32: Restore clearing of MSR[RI] at interrupt/syscall exit

    Commit 13799748b957 ("powerpc/64: use interrupt restart table to speed
    up return from interrupt") removed the inconditional clearing of
    MSR[RI] when returning from interrupt into kernel. But powerpc/32
    doesn't implement interrupt restart table hence still need MSR[RI]
    to be cleared.

    It could be added back in interrupt_exit_kernel_prepare() but it is
    easier and better to add it back in entry_32.S for following reasons:
    - Writing to MSR must be followed by a synchronising instruction
    - The smaller the non recoverable section is the better it is

    So add a macro called clr_ri and use it in the three places that play
    up with SRR0/SRR1. Use it just before another mtspr for synchronisation
    to avoid having to add an isync.

    Now that's done in entry_32.S, exit_must_hard_disable() can return
    false for non book3s/64, taking into account that BOOKE doesn't have
    MSR_RI.

    Also add back blacklisting syscall_exit_finish for kprobe. This was
    initially added by commit 7cdf44013885 ("powerpc/entry32: Blacklist
    syscall exit points for kprobe.") then lost with
    commit 6f76a01173cc ("powerpc/syscall: implement system call
    entry/exit logic in C for PPC32").

    Fixes: 6f76a01173cc ("powerpc/syscall: implement system call entry/exit logic in C for PPC32")
    Fixes: 13799748b957 ("powerpc/64: use interrupt restart table to speed up return from interrupt")
    Signed-off-by: Christophe Leroy [off-list ref]
    Signed-off-by: Madhavan Srinivasan [off-list ref]
    Link: https://patch.msgid.link/66d0ab070563ad460ed481328ab0887c27f21a2c.1757593807.git.christophe.leroy@csgroup.eu

 arch/powerpc/kernel/entry_32.S  | 18 +++++++++++++++++-
 arch/powerpc/kernel/interrupt.c |  2 +-
 2 files changed, 18 insertions(+), 2 deletions(-)

12. git revert 2997876c4a1a5864baa13d7393c2b68cf5b51183

After reverting the first bad commit, the kernel boots without any problems.