[TUHS] the device tree, hardware, and kernels.

[segaloco via TUHS]

On Monday, April 6th, 2026 at 15:50, Dan Cross via TUHS <tuhs at tuhs.org> wrote:

> I can kind of see it.  For a small SBC where devices are physically
> soldered onto the board, there's not a lot of expansion to be done:
> the device tree itself is pretty much static.  If you just plop it
> into an flash device or something, you can skip the full PROM
> monitor/Forth interpreter/option ROM thing.
>

Well and the prevailing SBC ecosystems aren't nearly as standardized as PC has historically been.  These devices don't have some least common denominator "I'm an 8086 with bus characteristics <xyz>" so the kernel needs a little more help.  DTB to me is better than having to go twiddling baked in kernel addresses at build time, then you really do need a kernel-per-machine rather than being able to spin a "defconfig" kernel that'll hopefully at least give you serial TTY on whatever you're messing with.  Plus, sometimes this means if you already have kernel support for device *xyz* in your current image and add one such device at some I/O address, you just have to rebuild your dtb rather than the kernel hiding all of that info deep inside.  Much lower risk to roll back a dtb than a whole kernel too.

Annoyingly it makes provision of quality documentation on memory maps and bus architecture a little worse, seems like you just have to "trust the dts" in many cases these days...

- Matt G.