PPC32: Boot regression on Nintendo Wii, after create_branch rework in 5.8

["Jonathan Neuschäfer" <j.neuschaefer@gmx.net>]

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Hi,

I recently booted my Wii again, and I noticed a regression at boot time.
Output stops after the "Finalizing device tree... flat tree at 0xXXXXXX"
message. I bisected it to this commit in the 5.8 development cycle:

commit 7c95d8893fb55869882c9f68f4c94840dc43f18f
Author: Jordan Niethe <jniethe5@gmail.com>
Date:   Wed May 6 13:40:25 2020 +1000

    powerpc: Change calling convention for create_branch() et. al.

    create_branch(), create_cond_branch() and translate_branch() return the
    instruction that they create, or return 0 to signal an error. Separate
    these concerns in preparation for an instruction type that is not just
    an unsigned int.  Fill the created instruction to a pointer passed as
    the first parameter to the function and use a non-zero return value to
    signify an error.

    Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Reviewed-by: Alistair Popple <alistair@popple.id.au>
    Link: https://lore.kernel.org/r/20200506034050.24806-6-jniethe5@gmail.com

 arch/powerpc/include/asm/code-patching.h |  12 +--
 arch/powerpc/kernel/optprobes.c          |  24 +++---
 arch/powerpc/kernel/setup_32.c           |   4 +-
 arch/powerpc/kernel/trace/ftrace.c       |  24 +++---
 arch/powerpc/lib/code-patching.c         | 134 ++++++++++++++++++-------------
 arch/powerpc/lib/feature-fixups.c        |   5 +-
 6 files changed, 119 insertions(+), 84 deletions(-)


Do you have any hints on how to debug and/or fix this issue?


Best regards,
Jonathan Neuschäfer

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