[Question] How to handle devices on non-standard busses

[nik012003]

Hi, I have my tablet's pen working on a downstream branch of linux mainline ( https://gitlab.postmarketos.org/panpanpanpan/sm8150-mainline ) and it will soon get supported by postmarket os and other distros.
The devices uses the spi bus, and is registered as such in the touchscreen/pen driver ( ts->input_dev->id.bustype = BUS_SPI ), without vendor/product ids.
What's the best option here to get it running with libwacom? Should I register it on a fake an I2C/usb bus on the drvier and assign an arbirary vid/pid? Or should I add SPI bus support in libwacom? in that case, how would I handle identification of the device since SPI doesn't really have vendor ids like usb does? systemd/evdev solves this by allowing dmi pattern matching for input devices.

[whot]

Adding spi would be quite trivial, just a few lines of additions where we currently have "usb" or "bluetooth". But without vid/pid that's a bit pointless.

We could extend the DeviceMatch handling for a dmi prefix and then treat the rest of it as modalias. That's more work but should be doable and seems to be what we needhere?

I won't have time to work on this in the near future but at least with the new-ish builder pattern this should be relatively trivial to add now if you want to have a go at that.

[nik012003]

Adding spi would be quite trivial, just a few lines of additions where we currently have "usb" or "bluetooth". But without vid/pid that's a bit pointless.

We could extend the DeviceMatch handling for a dmi prefix and then treat the rest of it as modalias. That's more work but should be doable and seems to be what we needhere?

I won't have time to work on this in the near future but at least with the new-ish builder pattern this should be relatively trivial to add now if you want to have a go at that.

Thank you for your input! I'll give it a shot and implement dmi pattern matching over the next few weeks.