There are some kernels for this NAS on the web (binaries and configs), but everything I could find was super old (like kernel 3.6.9 old). Because I’ve been able to successfully build current longterm version of Linus tree kernel, here is me sharing my solution.
It is based on this instruction. The kirkwood_defconfig was merged with mvebu_v5_defconfig so we are using the second one instead. I’ve pushed my config, patches and cross-compilation script to my github: https://github.com/sc0ty/nsa310-kernel. There is everything explained in README.md, I won’t repeat myself here. I’ll try to keep this repository up to date with Linus kernel as long as I am using this NAS myself.
And here are binaries (uImage with modules):