reserved-memory nodes created by OpenSBI

[Oleksii Kurochko]

Hello, dear community,

I would like to ask you about reserved-memory nodes, which are created
by OpenSBI here:
https://github.com/riscv-software-src/opensbi/blob/v1.2/lib/utils/fdt/fdt_fixup.c#LL198C5-L198C30)/

The questions are the following:
1. What is the purpose of extending dts by reserved-memory nodes? I
assume that it is necessary to reserve some memory ranges for OpenSBI.
2. Why OpenSBI needs to have a preserved memory?
3. The memory-reserved ranges are overlapped with Linux's memory node
range. Is it OK that OpenSBI's memory-reserved node ranges and Linux's
memory node ranges overlap?

Thanks.

~ Oleksii