cmake: Bump minimum cmake to 3.20.0

[ceolin]

Zephyr uses cmake 3.20.0 as the minimum version for a long time. Set the same requirement here to avoid possible issues in future.

[tomi-font]

Can we start marking those local patches (in the commit title) just as you did for the update to 3.6.4?

[ceolin]

Can we start marking those local patches (in the commit title) just as you did for the update to 3.6.4?

I want to document it first. It is better to come up with some agreement regarding tag names. We have discussed it in the security committee and there is a consensus about using it.

[valeriosetti]

I'm not against this change, but I have a question/doubt about the its goal.

In Zephyr we're currently building Mbed TLS by individually selecting source files to be included into the build (this happens in https://github.com/zephyrproject-rtos/zephyr/blob/main/modules/mbedtls/CMakeLists.txt) so from the Zephyr's perspective this change is irrelevant unless we plan to change the Mbed TLS' integration pattern to use CMake's add_subdirectory() instead. Is that the plan behind this change?

TF-M instead builds Mbed TLS using add_subdirectory() in the CMakeLists file, however TF-M main CMake file already sets the minimum version to 3.21, so I don't see the advantage also from this point of view.

[tomi-font]

I'm not against this change, but I have a question/doubt about the its goal.

In Zephyr we're currently building Mbed TLS by individually selecting source files to be included into the build (this happens in https://github.com/zephyrproject-rtos/zephyr/blob/main/modules/mbedtls/CMakeLists.txt) so from the Zephyr's perspective this change is irrelevant unless we plan to change the Mbed TLS' integration pattern to use CMake's add_subdirectory() instead. Is that the plan behind this change?

TF-M instead builds Mbed TLS using add_subdirectory() in the CMakeLists file, however TF-M main CMake file already sets the minimum version to 3.21, so I don't see the advantage also from this point of view.

I believe the goal is just to silence the warning caused by this when compiling TF-M indeed: zephyrproject-rtos/zephyr#92679

[tomi-font]

Force pushed to reference the Zephyr issue in the commit message.

[valeriosetti]

Force pushed to reference the Zephyr issue in the commit message.

Thanks! It looks clearer now to me :)

[frkv]

LGTM