Hi guys, I got a SPIdev overlay to work on the rock S0, figured I'd just share it here for the record, since I could have used this info myself (I spent days trying to figure it out since I had no experience with device trees or whatnot).
Basically, download the attached .dts file, then run
sudo armbian-add-overlay rk3308-spi2-spidev.dts
I also edited /boot/armbianEnv.txt and added this line, but I'm unsure if that's actually necessary?
param_spidev_spi_bus=2
This worked on Armbian 24.5.1 Noble, creating /dev/spidev2.0. You can verify that it works using this tool: https://github.com/rm-hull/spidev-test
The dts file is based on this one from radxa, however changed to "fragment@" syntax like other armbian overlays: https://github.com/radxa-pkg/radxa-overlays/blob/main/arch/arm64/boot/dts/rockchip/overlays/rk3308-spi2-spidev.dts
Maybe this will also work on Rock Pi S, but haven't tested.
rk3308-spi2-spidev.dts