linux-kernel - Re: [patch V2 00/18] mm/highmem: Preemptible variant of kmap

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Date:   Sat, 31 Oct 2020 22:33:33 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
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        Michal Simek <monstr@...str.eu>,
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        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
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        linux-xtensa@...ux-xtensa.org, Juri Lelli <juri.lelli@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch V2 00/18] mm/highmem: Preemptible variant of kmap_atomic & friends

On Sat, Oct 31, 2020 at 4:04 PM Christophe Leroy
<christophe.leroy@...roup.eu> wrote:
> > There are also some users on 10+ year old 32-bit netbooks or
> > business laptops, both x86 and Apple G4.
> > The longest-lived 32-bit embedded systems with large memory
> > (other than Arm) are probably NXP QorIQ P20xx/P40xx used in
> > military VME bus systems, and low-end embedded systems based
> > on Vortex86.
> > I'm less worried about all of these because upstream kernel
> > support for ppc32 and x86-32 is already bitrotting and they will
> > likely get stuck on the last working kernel before the
> > TI/Renesas/NXP Arm systems do.
> >
>
> Upstream kernel support for ppc32 is bitrotting, seriously ? What do
> you mean exactly ?

I was thinking more of the platform support: out of the twelve
32-bit platforms in arch/powerpc/platforms/, your 8xx is the only
one listed as 'maintained' or 'supported' in the maintainers list,
and that seems to accurately describe the current state.

Freescale seems to have practically stopped contributing to any of
their 32-bit platforms in 2016 after the NXP acquisition and no longer
employing either of the maintainers. Similarly, Ben seems to have
stopped working on powermac in 2016, which was ten years after
the last 32-bit hardware shipped for that platform.

> ppc32 is actively supported, with recent addition of support of
> hugepages, kasan, uaccess protection, VMAP stack, etc ...

That is good to hear, I didn't know about these additions.
What platforms are people using to develop these? Is this
mainly your 8xx work, or is there ongoing development for
platforms that need highmem?

         Arnd