On Fri, Oct 4, 2019 at 4:23 PM Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote:
>
> How is it relevant whether the boot CPU is A5 or A7? These are bL
> little cores that only implement NEON for feature parity with their bl
> big counterparts, but CPU intensive tasks are scheduled on big cores,
> where NEON performance is much better than scalar.
>
> If we need a policy for this in the kernel, I'd prefer it to be one at
> the arch/arm level where we disable kernel mode NEON entirely, either
> via a command line option, or via a policy based on the the types of
> all CPUs.
I don't think there was ever a b.L system with an A5, and most of the
A7+A15 systems did not age well, being high-end phone chips in
2014 that quickly got replaced with A53 parts and that no longer
get kernel upgrades.
The only chips I can think of that one might still care about here
are Exynos 542x (Chromebook 2 EOL 2019, Odroid XU4 ) and
Allwinner A80 (Cubieboard 4).
Just checking for Cortex-A7 being the boot CPU is probably
sufficient, that takes care of the common case of all the
A7-only embedded chips that people definitely are going to care
about for a long time.
Arnd
