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

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Date:   Wed, 9 Mar 2022 17:38:19 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Vladimir Murzin <vladimir.murzin@....com>
Cc:     Robin Murphy <robin.murphy@....com>,
        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>,
        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 5:21 PM Vladimir Murzin <vladimir.murzin@....com> wrote:
> On 3/9/22 4:17 PM, Arnd Bergmann wrote:
> > 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.
> >
>
> I'd appreciate if you keep them since I run Cortex-R52...

Ok, no problem.

Any opinion on removing CPU_ARM{7TDMI,740T,940T,946E}?

       Arnd