linux-kernel - Re: Old platforms: bring out your dead

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Date:   Wed, 13 Jan 2021 12:02:29 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Krzysztof Adamski <krzysztof.adamski@...ia.com>,
        Oleksij Rempel <o.rempel@...gutronix.de>,
        Baruch Siach <baruch@...s.co.il>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Daniel Tang <dt.tangr@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Jamie Iles <jamie@...ieiles.com>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Jonas Jensen <jonas.jensen@...il.com>,
        Marc Gonzalez <marc.w.gonzalez@...e.fr>,
        Hartley Sweeten <hsweeten@...ionengravers.com>,
        Lubomir Rintel <lkundrak@...sk>,
        Neil Armstrong <narmstrong@...libre.com>,
        Shawn Guo <shawnguo@...nel.org>, Alex Elder <elder@...aro.org>,
        Alexander Shiyan <shc_work@...l.ru>,
        Koen Vandeputte <koen.vandeputte@...ntric.com>,
        Hans Ulli Kroll <ulli.kroll@...glemail.com>,
        Vladimir Zapolskiy <vz@...ia.com>,
        Wei Xu <xuwei5@...ilicon.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Mark Salter <msalter@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Subject: Re: Old platforms: bring out your dead

On Wed, Jan 13, 2021 at 11:31 AM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
>
> On Sat, Jan 9, 2021 at 12:58 AM Arnd Bergmann <arnd@...nel.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