MMIO access without going through HAL/drivers

I have noticed that some code accesses memory-mapped I/O (MMIO) without going through Hardware Abstraction Layer (HAL) or drivers. This type of access may have several drawbacks, including poor portability and reusability.

I would like to open this issue to investigate why some MMIO access does not follow the conventional path through HAL or drivers. Are there specific scenarios where non-conventional MMIO access is preferred or a must (e.g. because, for example, SDK does not provide the necessary API)? Is it possible to fix the code by accessing MMIO conventionally (i.e. through HAL/drivers)?

Code snippets with MMIO access that does not go through HAL or drivers:
https://github.com/apache/nuttx/blob/f0825c240259a53753ee5ca38c7e2e4bf09a7d07/sched/init/nx_bringup.c#L267