On Wed, Jul 31, 2024 at 7:29 PM Arnd Bergmann [off-list ref] wrote:

=== ARMv4 ===

This is used for both StrongARM and FA526 CPUs, which are still
used on a small number of boards. Even the newest chips (moxa
art, ) are close to 20 years olds but were still in use a few years
ago. The last Debian release for these was Lenny (5.0).

Dropping compiler support now would be appropriate IMHO, and
we can drop kernel support in a few years.

I am actively using the Gemini as my NAS with OpenWrt and there
are several users of it in the OpenWrt community.

I don't know if there are enough of us to keep ARMv4 support in
GCC, but ARMv4 support has been added to CLANG (along
with ARMv4t), and I have tested to compile kernels for these
devices with CLANG (for testing CFI!) and they work fine, so if
GCC drops it, we can still build them with CLANG where it apparently
isn't a maintenance burden given that it was recently added.

Maybe CLANG has a more adaptive backend?

=== Highmem ===

Most Arm machines are fine without highmem support and can
use something like CONFIG_VMSPLIT_2GB to address up to 2GB
of physical memory. Machines larger than only popped up
around the time of the Cortex-A15 in 2012 and for the most
part got replaced by 64-bit chips within a short time.
In addition, there are also a handful of Cortex-A9 and
Marvell CPU based machines that have either more than 2GB
of RAM or a very sparse memory map that requires highmem
support.

Linus Walleij has done some work towards being able to use
up to 4GB of RAM with LPAE (Cortex-A7/A15 and later)
machines, which I think still needs to be finished before
we can remove support for highmem.

This is either really hard, or I'm a bad developer. But I keep
churning it.

=== Gemini, Moxart ===

These both use the Faraday FA526 CPU core that like
StrongARM implements ARMv4 rather than ARMv4T with thumb.

The chips are also over 20 years old, but the kernel
code has been updated and is not a maintenance burden
by itself, so there is no value in removing these
machines until StrongARM is also gone.

On the other hand, removing both FA526 and StrongARM
platforms means we can probably remove ARMv4 (non-T),
OABI and NWFPE support more quickly if we want, or
we can wait until a few years after gcc drops ARMv4.

OpenWRT lists the gemini platform as supported in
https://openwrt.org/docs/techref/targets/gemini, but
none of the individual machines have builds for the
current release.

Need input from Linus Walleij.

Yeah we use these devices. I don't know what counts as big
enough community to be considered, it's at least not just
me.

Gemini builds are in the official OpenWrt repos:
https://downloads.openwrt.org/releases/23.05.4/targets/gemini/generic/

Yours,
Linus Walleij