config: Allow Mbed to implement TIMING_C

[Patater]

Description

Mbed OS now provides POSIX-like time functions, although not alarm() nor
signal(). It is possible to implement MBEDTLS_TIMING_ALT on Mbed OS, so
we should not artificially prevent this in check-config. Remove the the
check that prevents implementing MBEDTLS_TIMING_ALT on Mbed OS.

Note that this limitation originally was added in the following commit,
although there isn't much context around why the restriction was
imposed: 63e7eba ("Add material for generating yotta module"). In
2015, Mbed OS was quite a different thing: no RTOS, no threads, just an
asynchronous event loop model. I'd suppose the asynchronous event loop
model made it difficult before to implement MBEDTLS_TIMING_C on Mbed OS,
but that is no longer the case.

Fixes #4633

Signed-off-by: Jaeden Amero [email protected]

Status

READY

Requires Backporting

When there is a bug fix, it should be backported to all maintained and supported branches.
Changes do not have to be backported if:

• This PR is a new feature\enhancement
• This PR contains changes in the API. If this is true, and there is a need for the fix to be backported, the fix should be handled differently in the legacy branch

Yes

• development_2.x

Others branches if desired, although likely not useful because Mbed OS doesn't integrate versions other than the latest 2.x at the moment and this bug fix is only relevant for Mbed OS.

Migrations

NO

Additional comments

Any additional information that could be of interest

Todos

• [ ] Tests Removing unnecessary check-config check
• [ ] Documentation
• Changelog updated
• Backported

Steps to test or reproduce

Implement MBEDTLS_TIMING_ALT for Mbed OS, and get blocked by this legacy check which doesn't make sense anymore.

[Patater]

Thanks for the quick review. Backport raised to development_2.x at #4635

[stevew817]

Am I the only one who finds it strange to see an mbed-specific check in an otherwise target-agnostic file? Shouldn't this rather be checked by the adaptation layer calling mbed TLS from mbed OS?