Where to find the documentation explaining some hps I/O function?

Yes, documentation is very big and helpful on 20% for unpractised beginners, is no reply on question "why?" and "why just so?", and only "take that we give and be glad!" :)

I ask Altera to add in SoC EDS distribution all used pdf-s with creating HWLIB or direct links to it on sites of owners with comment in .c, which .pdf-s used for developing.

You must say concrete point in HWLIB, where is understanding.

Mainly will need search in arm.com (infocenter.arm.com) and ug_embedded_ip.pdf from Altera.

Let in alt_interrupt.c many comments "See GIC 1.0", which not found on ARM site :)

P.S. Or best way -- in chorus ask Altera for write normal HWLIB documentation with man participation, not through heartless Doxygen ! :)

...Or independently write it on Wiki... Suddently somebody understand something... :)