I think that it is specifically the interaction between ihidev and ACPI. The hardware devices themselves are PS/2, with a vendor-specific extension to PS/2 activated by a special handshake, plus I2C. (On machines from 2024 that come with 9 USB root hubs; such is the inertia of laptop design.)
* https://gnats.netbsd.org/60897
I think that it is specifically the interaction between ihidev and ACPI. The hardware devices themselves are PS/2, with a vendor-specific extension to PS/2 activated by a special handshake, plus I2C. (On machines from 2024 that come with 9 USB root hubs; such is the inertia of laptop design.)