Ghost Bluetooth on Linux: how btusb wedges the MediaTek MT6639 trying to load firmware that isn't there.
I bought an ASUS ProArt X870E-Creator WiFi and Wi-Fi worked on the first boot. Bluetooth did not. No adapter ever showed up, and worse: the device was not in lsusb at all. Not failing, not erroring — absent. My first guess was the obvious one, and it was half right: the Bluetooth firmware for this chip does not ship in linux-firmware. What I did not expect is that the missing firmware is not what breaks the hardware. What breaks it is what the driver does about it. ...