Looking at - https://git.trustedfirmware.org/trusted-firmware-m.git/tree/app/main_ns.c#n90
**tfm_ns_wait_for_s_cpu_ready() -> tfm_platform_ns_wait_for_s_cpu_ready()** return a `PLATFORM_MAILBOX_SUCCESS` which seems to be very low level code, shouldn't it be `TFM_SUCCESS` ?
There may be some platforms other than PSoC6, which doesn't require tfm_ns_wait_for_s_cpu_ready() implementation. "PLATFORM_MAILBOX_SUCCESS" is a low-level error code and should be replaced by "TFM_SUCCESS".