Re: [PATCH 00/12] arm64: Remove unused big-endian support

[Will Deacon]

Hi Arnd,

On Tue, Aug 11, 2026 at 05:11:47PM +0200, Arnd Bergmann wrote:
> On Tue, Aug 11, 2026, at 16:01, Will Deacon wrote:
> > Big-endian support on arm64 (CONFIG_CPU_BIG_ENDIAN) has depended on
> > BROKEN since 1cf89b6bf660 ("arm64: Kconfig: Make CPU_BIG_ENDIAN depend
> > on BROKEN") and has already seen some clean-up patches removing some of
> > the unused support code (e.g. 5276ea17a23c ("lib/crc: arm64: Assume a
> > little-endian kernel")).
> >
> > Finish the job, and remove the remaining big-endian support code from
> > arm64. Note that the SETEND emulation for 32-bit tasks remains and so
> > some of the mixed-endian EL0 helpers are retained.
> 
> I had not expected the removal to come this soon, but I'm not
> complaining about that. I assume you are planning this for 7.4,
> leaving 7.3-LTS to still have the code in case someone wants to
> still use it, right?

Yes, this is for 7.4.

> Not sure if you saw
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/arch/arm/mm/Kconfig?id=fe91e4e9da70765420538d9cbcf6d9a970237a8d
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/arch/arm/mach-ixp4xx/Kconfig?id=2262f02ac2aa545560a7f182c8e6b5c98e72763c
> 
> so for 7.3, we have marked big-endian mode in arm32 as deprecated
> as well, and also managed to get ixp4xx working again in little-endian
> mode, which was slightly broken for a few years. It may be good to
> add a reference to your series for context.

Thanks, I'll do that!

> My suggestions there was to possibly remove arm32 big-endian mode at
> the same time as on arm64, but that does feel a little rushed if
> ixp4xx only has one release of supporting both, and removing be8
> but leaving be32 for a little while longer is probably not worth it.

Yeah, maybe give it another LTS on the arm32 side? I think arm64 going
first is ok, though.

> > I've broken this down into fairly coarse chunks, as it seemed a lot
> > easier to manage than one giant patch (even with the Kconfig being
> > effectively disabled already) and not all of it is just mindless
> > deletion. Despite that, I'm anticipating the whole thing going via the
> > arm64 tree.
> 
> I would have done even larger patches, this does already feel fairly
> fine-grained to me ;-). I had a look at the individual patches to make
> sure this all makes sense, and I found nothing wrong here.

If it was just a sed script or similar, I think I'd would've done a giant
patch, but some of it is surprisingly error-prone (e.g. when you have a
file with a load of '#ifdef CPU_BIG_ENDIAN' and then an '#ifndef
CPU_BIG_ENDIAN' hiding in the middle of it all).

> For a 7.4 (or later) merge:
> 
> Acked-by: Arnd Bergmann <arnd@xxxxxxxx>
> 
> There are also a few arm64 specific drivers that I think no
> longer need a dependency, but none of that is important:

I think there might also be some logic in the SMMUv3 driver which could
go. Perhaps I'll add a driver patch on the end of the next version to
pick this up.

Cheers,

Will