Bluetooth no longer working on Intel Surface Laptop 4/AX201

[jchv]

I have an Intel Surface Laptop 4 which has a Bluetooth adapter, 8087:0026 Intel Corp. AX201 Bluetooth, using the btusb driver. On the 6.6.13 kernel, the firmware seems to fail to load:

Bluetooth: hci0: Failed to load Intel firmware file intel/ibt-19-0-4.sfi

It was working properly in 6.6.10, so I think it broke in one of the recent updates to nixos-hardware.

I'm not sure where exactly the issue lies, but it seemed worthwhile to leave a report somewhere so that it can be found via search engines. I don't have time to triage at the moment, I will try to look into this soon...

[jchv]

Yeah, I updated to latest nixos-hardware and let it build, and it's still not right. Maybe I'll need to bisect it to figure out exactly what did it.

However, I temporarily worked around the problem by doing the evil thing of remounting the /nix/store as writable and injecting the missing files ibt-19-0-0.sfi and ibt-19-0-4.ddc into my modules dir /nix/store/mzb99aqm1v4s2553n3bkiy6gga028ahs-linux-firmware-20240115-xz and doing sudo modprobe -r btusb && sudo modprobe btusb to reload. In a pinch, this works (though I am curious if there is a less horrid way to patch my way around temporarily) and I'll have to remember to undo this (and fix the purity of my nix store) afterwards when I go to debug this.