linux-kernel - Re: [PATCH] ARM: Make sure CPU

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Message-Id: <7d0b68d4-6798-43a5-a6ca-99807bc183c5@app.fastmail.com>
Date: Fri, 03 Oct 2025 01:02:58 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Franz-Josef Haider" <fj.haider@...look.com>,
 "Linus Walleij" <linus.walleij@...aro.org>
Cc: "Russell King" <linux@...linux.org.uk>,
 "Ard Biesheuvel" <ardb@...nel.org>,
 "Russell King" <rmk+kernel@...linux.org.uk>,
 "Eric Biggers" <ebiggers@...nel.org>,
 "Nathan Chancellor" <nathan@...nel.org>,
 "Steven Rostedt" <rostedt@...dmis.org>, "Kees Cook" <kees@...nel.org>,
 "Dave Vasilevsky" <dave@...ilevsky.ca>, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, trivial@...nel.org
Subject: Re: [PATCH] ARM: Make sure CPU_ARM940T kernel can be built.

On Thu, Oct 2, 2025, at 17:34, Franz-Josef Haider wrote:
> On 10/1/25 23:52, Arnd Bergmann wrote:
>
> Ok if the support for ARMv4T NOMMU has been removed, then maybe we can 
> leave this as resolved.
>
> It's actually just for a hobby project, nothing important. I just 
> thought these two patches might be helpful to other people who 
> encounter a similar issue on similar cpus, but if the support for 
> ARMv4T NOMMU has been dropped then there is no point maybe.
>
> Here are the patches for 6.2 in any case but it's very much a hacky 
> WIP, and there is some stuff in there that's not needed anymore on top 
> of later commits. https://github.com/krnlyng/linux-ipod/commits/n2g-wip
> I also have a version on top of a recent (~29 SEPT 2025) commit locally 
> if that is interesting too.

Looking at your tree, I find that the ARMv4T NOMMU support is not
even that bad to put back, especially since commit 84fc86360623
("ARM: make ARCH_MULTIPLATFORM user-visible") made it possible to
add a 'depends on !ARCH_MULTIPLATFORM' in the platform specific
code.

I still think that this specific oneline patch is not helpful,
but the other one you sent is technically still a correct fix
and we should either merge that or drop the remnants of the
ARM740T/940T/946E code now that we know it's broken.

Similarly, the later ARM1176 based code that you based your
patches on does look worth cleaning up and merging if there are
still users.

For the specific s5l870x (arm940) SoC support, I see what you
mean with missing cleanups, but more importantly I think that
we will want to drop nommu support from arch/arm/ in a few years
as the remaining users all tend to fall into a similar class
as yours where the developers work on them for the fun of it
but without anyone else depending on it to run on the latest
kernels. Since there is a significant cost in continuing to
test and fix the special cases for nommu support overall, I
would prefer to draw the line at S5L8720 support and not merge
S5L8702 or earlier.

      Arnd