Looking at the 5.10.4 Linux kernel source for the BL808 SoC here:
https://github.com/bouffalolab/bl808_linux
I see it's carrying this patch that was rejected upstream to add support for non IO coherent SoCs:
https://lore.kernel.org/lkml/1555947870-23014-1-git-send-email-guoren@kernel.org/
I couldn't find any information in the BL808 Reference Manual (v1.1) that described the coherency model, but I assume this means the D0 CPU does not support DMA coherency?
