Integrating Bluetooth module using HCI USB

[benjamin....@endian.se]

We have a board based on imx6 sabresd that we're porting Android to. Thanks to a regression in the NXP Oreo BSP we had to revert to Nougat. 

This board has a mini PCIE Bluetooth module (RTL8821ae) that talks HCI USB. The driver seems to be integrated (hci0 file gets created etc) but I am not sure how to integrate the module further. bt_vendor.conf only contains references to a UART port and this device doesn't use UART.

It was my impression that Bluedroid lacked USB HCI support, but that Fluoride added it. Of course, documentation on Fluoride is impossible to find, so I'm not even sure this is true. I've tried going the opposite direction by doing HCI protocol conversion, using a patched socat that supports HCI, but I can't get that to work (socat closes the socket with -ENETDOWN when I start bluetooth_manager). I've also found a git repo, "libbt-usb", that claims to convert HCI USB to HCI UART, but I can't get it to build on Nougat.

Can anyone point me to a reference describing what is needed to integrate this card into the Android stack? Is it even possible/feasible? Any help would be greatly appreciated...

[Tranphong Vu]

Hi friend, 

It seem you miss vendor lib . I assume your Bluetooth device driver already probed and creat a usb hci device. Your vendor lib will talk to usb hci device. 

In the past, I met a hci USB Bluetooth device. It’s kernel driver create a device at /dev/* and I have a vendor lib to talk to this device. It’s name seem like libbt_vendor. 

In your case I think you need to check the driver that creat hci0 device, check all feature that driver support in ioctl, open ... and check the interface that fluoride requires for a Bluetooth vendor lib. Then follow this to implement Bluetooth vendor lib. I don’t think it is a easy job . You should contact the ihv of your Bluetooth device and ask them a Bluetooth vendor lib.

Vào Th 2, 25 thg 2, 2019 lúc 22:00 <benjamin....@endian.se> đã viết:

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[Benjamin Lindqvist]

Hi Tranphong,

It seems the consensus is that there is no easy ways (such as HCI
protocol conversion) to do this. I don't believe Realtek will be that
keen on implementing a vendor lib, especially given that Android seems
to have changed the HAL interface with 8.0, so I may have no choice but
to do it myself.

Thanks for your response though, it was very helpful. If you happen to
have any references (Github links, etc) on the HCI/USB interface you
mentioned, I'd be very grateful if you could share them so I could use
it as a starting point.

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Benjamin Lindqvist
Endian Technologies AB