As https://www.armbian.com/tinkerboard/ has a quite fresh 4.14 Linux kernel (in Armbian Stretch Next Desktop 5.50) I am trying to use that instead of the standard TinkerOS 2.0.7 with a 4.4.103 kernel.
However, Armbian is configured to provide only spidev2.0, while TinkerOS can have spidev0.0, spidev0.1, spidev2.0 and spidev2.1 all enabled at the same time as long as you disable UART4 which shares GPIO header pins with SPI0. In the TinkerOS case, there is a config tool which edits a small and straightforward text file in /boot/ containing lines such as "intf:spi0=on" or "intf:uart4=off". The corresponding Armbian file seems to be /boot/armbianEnv.txt - possibly with overlays=... lines and DTS files. There also is a tool called armbian-add-overlay to load (at runtime?) DTS files...
Given that the diff between the sorted device trees (using dtc to sort them) is 3200 lines, not counting context, compared to 3700 and 2600 lines respectively for the complete device trees of both distros in DTS format, it seems hopeless for me to write a DTS to switch UART4 off and SPI0 on and enable the second CS line on SPI2. But maybe I am missing something here and there is an already existing easy way to switch the following devices on and off?
SPI0, SPI2
PWM2, PWM3
UART1, UART2, UART3, UART4
I2C1, I2C4
PCM_I2S
and possibly other Armbian specific features :-)
I personally had everything except UART2 and UART4 on in the TinkerOS case and am trying to reproduce that in Armbian. The SPI items are my priority.
Another strange issue is that the package repositories contain, among others, the headers and source code of Linux 4.14.34 and 4.14.14 respectively, but I can not find the exact sources needed to rebuild the 4.14.52 kernel used by the current Armbian Stretch 5.50 desktop edition.
In general, the Armbian repositories seem to be quite up to date compared to TinkerOS which only has the sources on Github and still uses quite old 4.4 kernels, but I do need that full SPI connectivity, so I hope that the Armbian forum has some hints for me. Thank you!