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Date:   Mon, 24 Jul 2023 12:59:56 -0400
From:   William Breathitt Gray <william.gray@linaro.org>
To:     Linus Walleij <linus.walleij@linaro.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        William Breathitt Gray <vilhelm.gray@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Cooper <andrew.cooper3@citrix.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Wei Liu <wei.liu@kernel.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Juergen Gross <jgross@suse.com>
Subject: Re: [patch 00/58] x86/apic: Decrapification and static calls
Message-ID: <ZL6uDN4KmYTk8R1J@fedora>
References: <20230717223049.327865981@linutronix.de>
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On Tue, Jul 18, 2023 at 04:29:23PM +0200, Linus Walleij wrote:
> On Tue, Jul 18, 2023 at 1:14=E2=80=AFAM Thomas Gleixner <tglx@linutronix.=
de> wrote:
>=20
> > This builds and boots on 32bit and 64bit, but obviously needs a larger =
test
> > base especially on those old 32bit systems which are just museum pieces.
>=20
> These things are indeed museum pieces if you think servers, desktops
> and laptops. They will at max be glorified terminals.
>=20
> What we noticed on ARM32 is that it used for:
> 1. Running 32-bit kernels as guests in virtual machines (I don't know if
>   x86 has this problem, sorry I'm ignorant there)
> 2. Embedded systems with very long support cycles
>=20
> For x86 there is PC104, I think William Breathitt Gray knows more about
> those, scope and usage etc. The typical usecase is industrial embedded
> (I've seen quite a few e.g biochemical lab equipment set-ups) which are
> running on a "it works don't fix it"-basis but they are network connected
> so they may need new kernels for security reasons, or to fix bugs.
> https://en.wikipedia.org/wiki/PC/104
>=20
> These things have lifecycles that easily outspans any server, desktop or
> laptop. 30+ years easily. They are just sitting there, making whatever
> blood cleaning agent or medical.
>=20
> I think the automation people have mostly switched over to using
> ARM things such as RaspberryXYZ for new plants, but there is some
> poor guy with the job of keeping all the PC104 plants running on recent
> kernels for the next 20 years or so.
>=20
> Yours,
> Linus Walleij

It's true that there a still a good number of PC104 setups still running
out there in the manufacturing sector. However, it should be noted that
these are typically systems that are configured and set once, left to
run indefinitely doing their specific manufacturing task until the
machines invariably break down from wear a decade or so later.

It's rare for the software of these systems to be updated; where a
machine fails, the owner will usually repair or replace the particular
mechanical component and reload that same ancient software they have
been using for years. The cases where software is updated may be out of
necessity to support a replacement device for a component that is no
longer in production. In these situations, you would find newer PC104
devices to fill that gap: where compatibility is needed with the ancient
core machine featuring only an ISA bus, but which the plant owner
doesn't want to throw away because "it still runs just fine with a
little spit shining."

Perhaps some years ago I would have said there was still demand for
PC104 support, but now with the motherboards of these older systems
finally failing due to age, the owners of these machines are forced to
upgrade to something newer. As mentioned, I've also seen a general trend
in this sector to move towards ARM products, perhaps out of a desire for
lower power consumption or maybe their industrial line of features.
Overall I don't see much future for PC104 in newer kernels because as
the systems using it fail, users are switching to platforms without it.

William Breathitt Gray

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