Having a bluetooth dongle recognized by our c-91 upgrade can be damn tricky. After buying 3 different models that seemed not to be recognized at all, I got quite nervous and decided to look a bit further into this stuff.
Here is what I've found:
first of all, the driver is not compiled as a btusb module for zenithink kernel, it seems the driver is compiled into the kernel itself,
I got one of my three not-recognized dongles, plugged in and restarted the tablet.
after that I got to android settings and tried to turn bluetooth on, no result as usual, the slider went back to off after few seconds without further notice.
Normally that would make you assume your dongle doesn't work, and you usually give up, but wait... let's go back to old-style linux tools:
At this point you need a terminal emulator for Android, one that can be granted superuser permissions, I use this one:
https://play.google....pal.androidterm
open the terminal emulator and digit:
su (all this stuff must be made as root, unfortunately)
hciconfig
if your dongle has actually been recognized by the kernel you should get something like this
hci0: Type: USB
BD Address: 00:15:92:3F:0A:57 ACL MTU: 310:10 SCO MTU: 64:8
DOWN
RX
bytes:967 acl:0 sco:0 events:28 errors:0
TX
bytes:367 acl:0 sco:0 commands:28 errors:0
if you got this, the device is there and recognized, and there is no particular reason Android should not be able to use it, so, on the terminal digit:
hciconfig hci0 up
at this point, if you try hciconfig again you should have:
hci0: Type: USB
BD Address: 00:15:92:3F:0A:57 ACL MTU: 310:10 SCO MTU: 64:8
UP RUNNING
RX
bytes:967 acl:0 sco:0 events:28 errors:0
TX
bytes:367 acl:0 sco:0 commands:28 errors:0
bingo! but be careful: if you go to Android bluetooth settings and try to turn bluetooth on you will probably have no result yet, and it would seem it get stuck.
we need a last trick, and so, on the terminal emulator you should try to digit
hcitool scan
at this point if your dongle has some sort of status led, it should go on, and that means good news, get back to android bluetooth settings, and there it is!
Your damn dongle is working at last!!!
hope this can be of some help for other users with a bunch of bluetooth dongle lying sadly abandoned on their desk