This happens on my machine as well. I'm running buster with 4.16 kernel and firmware-realtek is installed. It seems that this file should be in the package but it hasn't been include for some reason, even though it is available from https://githu b.com/lwfinger/rtl8723au_bt/.
Installing the file on /lib/firmware/rtl_bt/ solves the issue. On Fri, 23 Mar 2018 19:02:48 +0100 "Rathorian" <cont...@rathorian.fr> wrote: > Package: firmware-realtek > Version: 20161130-3 > Severity: important > > Dear Maintainer, > > Every time I start Debian, I get an error message saying: > "bluetooth hci0: firmware: failed to load rtl_bt/rtl8821a_config.bin" > > I have also tried to install the package since stretch-backports, without > any success. > > Cordially > Rathorian > > -- System Information: > Debian Release: 9.4 > APT prefers stable-updates > APT policy: (500, 'stable-updates'), (500, 'stable') > Architecture: amd64 (x86_64) > > Kernel: Linux 4.9.0-6-amd64 (SMP w/4 CPU cores) > Locale: LANG=fr_FR.utf8, LC_CTYPE=fr_FR.utf8 (charmap=UTF-8), > LANGUAGE=fr_FR.utf8 (charmap=UTF-8) > Shell: /bin/sh linked to /bin/dash > Init: systemd (via /run/systemd/system) > > firmware-realtek depends on no packages. > > firmware-realtek recommends no packages. > > Versions of packages firmware-realtek suggests: > ii initramfs-tools 0.130 > > -- no debconf information > -- -- []s, Francisco M Neto