System memory in jz4780

Hi, NetBSD developers. I have a question, maybe you could answer it.
It relates to Ingenic jz4780 SoC found in CI20 board.
It has TCSM - tightly coupled shared memory, from where ROM code's
payload runs before it initializes SDRAM. The payload is u-boot for
example. Processor address of TCSM is f4000000. It's kseg3, a mapped
segment. The question is how it works at the time the payload runs?
Architecturally it only could run if this area had appropriate tlb
entries. I've checked all the 32 tlb entries and didn't find there
anything valid. Don't you know how this works? Has Ingenic introduced
yet another unmapped region in the above part of kseg3?
Does NetBSD use these virtual addresses (>= f4000000)? Do they work?
And yet another question. Suppose I map SDRAM this way - BASE (in
DDRC) is 0x00 and MASK is 0x80. This means I have addresses from
0-7fffffff (2 GB) for SDRAM and since there is only 1GB of SDRAM, the
whole space will be split into two subspaces - lower and higher
aliases. Namely - [0 - 3f ff ff ff] and [40 00 00 00 - 7f ff ff ff].
Physical addresses of the range between 10 00 00 00 - 1f ff ff ff are
reserved for ROM, I/O and other. This is 256 MB. If I used the higher
aliases for this range (thus 50 00 00 00 - 6f ff ff ff) for SDRAM
accesses, would they get into SDRAM? They should, but I am not sure,
the specification isn't clear. How NetBSD does overcome this 256MB
reserved sub-range of the system space when referencing SDRAM physical
pages?