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

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Message-ID:
 <VI0P195MB27396082C4B72FDCDF18E775EDF1A@VI0P195MB2739.EURP195.PROD.OUTLOOK.COM>
Date: Fri, 24 Oct 2025 16:51:00 +0300
From: Franz-Josef Haider <fj.haider@...look.com>
To: Arnd Bergmann <arnd@...db.de>, 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 10/3/25 02:02, Arnd Bergmann wrote:
> 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

Ok, I think it would make sense to merge the other patch just for correctness sake or drop the ARM940T code entirely, but ofc it's not my decision to make.
I will ask the person who did the S5L8720 parts whether they want to cleanup&upstream the changes (I only did the S5L8702 parts).

Thanks and best regards,
Franz-Josef