Highmem on AXM and K2

[Arnd Bergmann]

On Wed, Apr 15, 2026, at 16:48, Stefan Wiehler wrote:
> Hi Arnd,
>
> I would like to inform you that after some internal discussion, we
> decided not to continue with my experiments to transition from
> VMSPLIT_3G towards VMSPLIT_2G{_OPT} on the K2. The K2 is used in a
> legacy product after all, and the more senior colleagues were quite
> concerned about making such a major change due to various hacks that
> might fall apart along the way.
>
> Therefore, we will go the CIP path by staying with the last SLTS kernel
> with full highmem support. Therefore, we would be very glad if this is
> the case for at least the next SLTS kernel, supposedly to be released in
> 2027, as we should then be able (despite barely) to meet our projected
> EOL of 2037. 

Hi Stefan,

The CIP kernel from 2027 should certainly still support highmem,
though I am in the process of removing highmem usage from drivers
that rarely use a lot of memory, which means you may see a
slightly higher memory consumption, and changing the default to
CONFIG_VMSPLIT_2G_OPT/CONFIG_VMSPLIT_2G means that your configuration
will see less testing in the future.

I don't think there is an immediate problem for your product
using the 2027 LTS kernel, or (most likely) the 2029 version,
but I'm still worried about the boot regression you reported
with CONFIG_VMSPLIT_2G, which means we still have to make sure
K2 works with the new default.

      Arnd