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

[Will Deacon <will@kernel.org>]

On Wed, Sep 24, 2025 at 09:09:16AM -0700, Guenter Roeck wrote:
> On 9/19/25 11:40, 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.
> > 
> > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: Marc Zyngier <maz@kernel.org>
> > Cc: Ard Biesheuvel <ardb@kernel.org>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: Hanjun Guo <guohanjun@huawei.com>
> > Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > Cc: Guenter Roeck <linux@roeck-us.net>
> > Link: https://lore.kernel.org/linux-arm-kernel/73701e9f-bee1-7ae8-2277-7a3576171cd4@huawei.com/ [1]
> > Signed-off-by: Will Deacon <will@kernel.org>
> > ---
> > 
> > Cc'ing Guenter as a heads-up in case he needs to turn down his testing
> > to avoid this causing a false regression report.
> 
> Cool, one more architecture to drop. I wonder if I should drop arm64 big endian testing
> for all kernel releases. That would simplify my test infrastructure substantially,
> and it would avoid useless regressions due to bitrot for older kernel releases
> if no one is using it anyway. Thoughts ?

It's entirely up to you, but I'd suggest leaving it running until 6.18
is out and then turning it all off if nobody has chimed in to say
they're using this stuff.

Will