linux-kernel - Re: [PATCH 2/2] ARM: remove support for NOMMU ARMv4/v5

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Date:   Wed, 9 Mar 2022 17:17:21 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Russell King <linux@...linux.org.uk>,
        Linus Walleij <linus.walleij@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        kernel test robot <lkp@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mark Rutland <mark.rutland@....com>,
        Vladimir Murzin <vladimir.murzin@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        Anshuman Khandual <anshuman.khandual@....com>
Subject: Re: [PATCH 2/2] ARM: remove support for NOMMU ARMv4/v5

On Wed, Mar 9, 2022 at 4:48 PM Robin Murphy <robin.murphy@....com> wrote:
>
> On 2022-03-09 14:40, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@...db.de>
> >
> > It is possible to build MMU-less kernels for Cortex-M base
> > microcrontrollers as well as a couple of older platforms that
> > have not been converted to CONFIG_ARCH_MULTIPLATFORM,
> > specifically ep93xx, footbridge, dove, sa1100 and s3c24xx.
> >
> > It seems unlikely that anybody has tested those configurations
> > in recent years, as even building them is frequently broken.
> > A patch I submitted caused another build time regression
> > in this configuration. I sent a patch for that, but it seems
> > better to also remove the option entirely, leaving ARMv7-M
> > as the only supported Arm NOMMU target for simplicity.
>
> In that case, it would probably make sense to garbage-collect all the
> configs, setup code and other stuff relating to older MMU-less CPU cores
> like ARM1156, ARM940, etc. at the same time.

Right, good idea. These are only selected by CONFIG_ARCH_INTEGRATOR,
but that in turn doesn't build for CONFIG_MMU=n because it depends on
ARCH_MULTIPLATFORM. I'll send a patch for these.

I also went back and forth between removing the #ifdefs in
arch/arm/mm/proc-*.S for this patch, though I did not do that in the end.
We may still want them at least for proc-v7.S because that is a small
chance that someone will want to support Cortex-R.

        Arnd