gpoulios commented on PR #16729:
URL: https://github.com/apache/nuttx/pull/16729#issuecomment-3077365957
@xiaoxiang781216 you merged it right before I was about to send this:
The problem I see now is that I overlooked that most arm defconfigs do not
explicitly enable `CONFIG_ARCH_USE_MMU`, and it defaults to `n`. The only
configs that enable it are:
- `avaota-a1:nsh`
- `qemu-armv8a:knsh`
- `imx93-evk:knsh`
- `imx93-evk:koptee`
Then most boards (even some of the above) just go on and initialize the MMU
without guarding on any kconfig
([eg](https://github.com/apache/nuttx/blob/4a765b557ffc0f7b6471483b266869016161be2f/arch/arm64/src/qemu/qemu_boot.c#L162)).
And that is even though the
[pgalloc()](https://github.com/apache/nuttx/blob/4a765b557ffc0f7b6471483b266869016161be2f/include/nuttx/arch.h#L781)
and
[sbrk()](https://github.com/apache/nuttx/blob/4a765b557ffc0f7b6471483b266869016161be2f/include/unistd.h#L375)
still depend on `CONFIG_ARCH_USE_MMU` being set!? What a mess.
So for OP-TEE driver, that means users of the OP-TEE driver on other configs
will enter the cache maintenance blocks even though they don't need to.
Ideally, we would want:
1. all arm configs to explicitly set `CONFIG_ARCH_USE_MMU=y`
2. wrap all calls to `arm{64}_init_mmu(true);` around `CONFIG_ARCH_USE_MMU=y`
3. fix
[this](https://github.com/apache/nuttx/blob/4a765b557ffc0f7b6471483b266869016161be2f/arch/arm64/src/common/arm64_cpustart.c#L224-L226)
to wrap around `CONFIG_ARCH_USE_MMU` instead of `CONFIG_ARCH_HAVE_MMU`.
That might be quite invasive though. But still, current use of
`CONFIG_ARCH_HAVE_MMU` vs `CONFIG_ARCH_USE_MMU` in nuttx arm(64) is wrong, even
semantically wrong (`HAVE` is always assumed to be `USE=y`, and `USE` is not
used almost at all). And this is inconsistent with the use of `USE_MMU` in
other architectures
([x86-64](https://github.com/apache/nuttx/blob/4a765b557ffc0f7b6471483b266869016161be2f/arch/x86_64/src/common/CMakeLists.txt#L57),
[risc-v](https://github.com/apache/nuttx/blob/4a765b557ffc0f7b6471483b266869016161be2f/arch/risc-v/src/common/CMakeLists.txt#L119)).
If you think it's a good idea to fix how `CONFIG_ARCH_USE_MMU` is used in
arm(64) I could give it a go.
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