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From:   Arnd Bergmann <arnd@kernel.org>
Date:   Wed, 13 Jan 2021 12:02:29 +0100
Message-ID: <CAK8P3a3gGKyTGPRh=VyJ8SZq-VXk-5ZFNu-WwssZmWVucy4bCQ@mail.gmail.com>
Subject: Re: Old platforms: bring out your dead
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Krzysztof Adamski <krzysztof.adamski@nokia.com>,
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On Wed, Jan 13, 2021 at 11:31 AM Andy Shevchenko
<andy.shevchenko@gmail.com> wrote:
>
> On Sat, Jan 9, 2021 at 12:58 AM Arnd Bergmann <arnd@kernel.org> wrote:
> >
> > After v5.10 was officially declared an LTS kernel,
>
> I have a question here. Maybe I have missed something, but how LTS
> helps in this case? LTS AFAIR has a rule "upstream first". How can you
> provide a patch to be backported if there is no upstream for it
> anymore?

Platform specific bugs are usually not the problem here, and if something
does happen on deleted code, I would expect you can get an exception
to the "upstream first" rule.

What I was getting at here were the things in the second category, the
stuff that is is still maintained and working, but so old that it becomes a
burden for maintainers. If a maintainer knows who all the users are
and what they do with their machines, removing the platform from mainline
would be a chance to get everyone to use the same LTS version so they
can get bugfixes to common kernel code for a few more years and
benefit from everyone else testing the same codebase.

> > * 80486SX/DX: 80386 CPUs were dropped in 2012, and there are
> >   indications that 486 have no users either on recent kernels.
> >   There is still the Vortex86 family of SoCs, and the oldest of those were
> >   486SX-class, but all the modern ones are 586-class.
> > * Alpha 2106x: First generation that lacks some of the later features.
> >   Since all Alphas are ancient by now, it's hard to tell whether these have
> >   any fewer users.
>
> We still have Intel Quark available. I run vanilla from time to time
> on it due to the presence of peripherals I can't find elsewhere on x86
> boards.

While Quark is derived from a i486 pipeline, the kernel treats it as
CONFIG_M586TSC, as it contains fpu, rdtsc, cpuid and cmpxchg8b
instructions but no cmov or mmx. More importantly, you wouldn't find the
vintage i486 peripherals (drivers/ide, drivers/video/fbdev, VLB, ISA,
floppy) but instead have modern stuff like USB, PCIe, and eMMC.

     Arnd