Re: [PATCH] arm64: Kconfig: Make CPU_BIG_ENDIAN depend on BROKEN

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

On Fri, Sep 19, 2025 at 07:40:25PM +0100, Will Deacon wrote:
> Big-endian arm64 configurations are vanishingly rare, yet we still claim
> to support them in Linux despite very limited testing or visible
> interest. Supporting big-endian adds unnecessary burden to reviewers and
> contributors which, without any known active users, is hard to justify.
> For example, recent work to improve our futex routines and to implement
> nested virtualisation support is non-trivially complicated by having to
> support both big- and little-endianness.
> 
> Back in 2019 [1], it was claimed that Huawei were using arm64 big-endian
> machines in their telecommunication products but I don't know whether
> that's still the case and certainly haven't seen any patch contributions
> to help support or maintain it.
> 
> Make CPU_BIG_ENDIAN depend on BROKEN as an initial deprecation step
> towards its removal.

As of this month (September 2025) there's a new community project [1,2]
to revive aarch64_be. Jens Reidel (CC'd) and I are involved in it. We've
been fixing several aarch64_be-related bugs, but mostly[3] in userspace,
because the kernel support is pretty solid.

So, just so it doesn't go unmentioned, there is interest in keeping
big-endian ARM64 alive.

Best regards,
J. Neuschäfer

[1]: https://aarch64.be/ (binary packages)
[2]: https://codeberg.org/neuschaefer/porting/src/branch/main/aarch64_be.md
     (status and documentation)
[3]: https://lore.kernel.org/lkml/20250726235646.254730-1-adrian@mainlining.org/