Message-Id: <96558a17-8c90-4092-a0b0-e128574f3d89@app.fastmail.com>
Date: Wed, 21 Aug 2024 07:51:04 +0000
From: "Arnd Bergmann" <arnd@...db.de>
To: "Alexander Dahl" <ada@...rsis.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 "Russell King" <linux@...linux.org.uk>,
 "Linus Walleij" <linus.walleij@...aro.org>,
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 "Nicolas Ferre" <nicolas.ferre@...rochip.com>
Subject: Re: [RFC} arm architecture board/feature deprecation timeline

On Wed, Aug 21, 2024, at 06:15, Alexander Dahl wrote:
> Am Wed, Jul 31, 2024 at 07:29:29PM +0200 schrieb Arnd Bergmann:
>> === ARMv5 ===
>> 
>> About one third of all supported platforms use ARMv5,
>> but most of these are near their end of support. Notably
>> there are still new SAM9 variants from Microchip that are
>> meant as backward-compatible replacements for their
>> older variants.
>> 
>> Debian still supports these, but the lack of FPU and
>> atomics makes this harder, so I expect this to become
>> an unofficial port in the future.
>
> FWIW, these are not only replacements, but actually new boards are
> designed with SAM9X60 for example.

Right, but I would assume that most of those board
designs using it are done because someone needs an
ARMv5 design in order to run a certain piece of
software, or because they are already invested in
Microchip's SAM9 ecosystem in other products.

For someone starting from scratch, there would be few
reasons to pick a SAM9 over e.g. an STM32MP1 with a
Cortex-A7 that is more capable in most ways but half
the cost.

> Not all have .dts files in mainline kernel, though.  Would that
> improve or change things with regard to long term platform support, if
> the .dts files were upstream?

I think upstreaming the dts files is mostly an advantage for
maintaining the specific boards, as it allows easier
integration into CI test environments and lets developers
see which drivers are used by a platform. Having at
least a couple of products with full dts files in addition
to the reference boards does help though.

For the at91 platform support itself in the kernel,
I don't see a real risk at the moment. There are a few
areas that make ARMv5 support risky in the long run:

- Debian support for the softfloat "armel" port will
  likely be moved into an inofficial port in the future,
  which in turn makes it harder for average kernel
  developers to test things. 

- There are discussions about making SMP support
  mandatory for all architectures in the kernel.
  If it gets to this, ARMv4T and ARMv5 support may
  need to end, unlike ARMv6K and up.

- Even longer in the future, all 32-bit kernel
  support will end. I don't expect this to happen
  for another 15 years, but the writing is on the
  wall.

      Arnd

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