Get more information about Allwinner F-Series

[soFPG]

I recently stumbled upon this news from late 2018: https://lore.kernel.org/patchwork/patch/877044/

As far as I understand correctly, they added support for the (very) old F-Series ARM7 & ARM5 based CPUs from Allwinner (http://linux-sunxi.org/Allwinner_SoC_Family).

Google lists only 5 pages of search results for "f1c100a". Among these results is not a reference manual - only a 39 pages long "datasheet" (http://dl.linux-sunxi.org/F1C100/Allwinner_F1C100_datasheet_20110331.pdf).

I don't get how anyone would adapt the linux kernel to a processor with only 39 pages of documentation - no register description whatsoever? How is that possible? How do I get my hands on the reference manual from Allwinner (if I don't want to buy those chips in million quantities)?