[RFC PATCH v2 1/7] ARM: zte: Add zx297520v3 platform support.

[Linus Walleij]

Hi Stefan,

On Fri, Jan 30, 2026 at 5:38 PM Stefan Dösinger
<stefandoesinger at gmail.com> wrote:
> Andre Przywara suggested switching to 64 bit via the Reset Management
> Register. The RMR seems to do nothing on this hardware (https://
> lists.infradead.org/pipermail/linux-arm-kernel/2026-January/1099787.html is my
> reply in the archives).
>
> We don't have board schematics or datasheets, but I guess AA64nAA32 is
> hardwired to 32 bit. Maybe a GPIO pin can control it, but it doesn't look like
> it. We also know of no way to reset the CPU without resetting the rest of the
> board. (since RMR doesn't seem to work)

How typical. Well maybe this is just a new breed of 32bit machine
after all.

> In my previous research I came across the suggestion to do an eret from EL3 to
> EL3 and set SCR_EL3.RW to 1. We'd obviously need to set ELR_EL3 to point to 64
> bit code. However, I haven't actually seen a working example of that and my
> own attempts just ended up locking up the CPU. I don't know where I came
> across the suggestion the first time.

It would be my intuitive idea as well. After all, ERET is the way we do a lot
of things, such as start processes in user mode. But if it doesn't work,
well then it doesn't :/

I don't have any other ideas than to proceed with a 32bit port.

Yours,
Linus Walleij