In the meantime I successfully installed Linux-libre kernel version 5.3 from
https://jxself.org/linux-libre/ – Unfortunately, my onboard Bluetooth
adapter is still not usable.
I identified the onboard adapter as
Device 'Bluetooth Device'
ID USB 0489:e04e
Class e0-01-01
Type bluetooth
Vendor Foxconn / Hon Hai
Name Bluetooth Device
See also https://linux-hardware.org/index.php?id=usb:0489-e04e
They say this Bluetooth device should be supported by mainline kernel
versions 3.2 and newer. I confirm that I have the needed kernel modules ath3k
and btusb both loaded. But I cannot say if its support was removed from
Linux-libre kernel.
So I still have to use an external USB Bluetooth adapter… Pity :-(
