Manjaro Linux vs. Dell Latitude E7250 Bluetooth

Although the Dell Latitude E7250 allegedly had Bluetooth capability and the Blueman applet tried connecting to my Bluetooth headsets, the connection aways failed and nothing worked. There’s a WLAN module stuck in an M.2 socket inside the laptop providing both WiFi and Bluetooth:

A bit of searching suggested the driver wasn’t loading properly, which became obvious after I knew where to look:

dmesg | grep -i blue
… snippage …
[    5.678610] Bluetooth: hci0: BCM20702A1 (001.002.014) build 1572
[    5.678851] bluetooth hci0: Direct firmware load for brcm/BCM20702A1-0a5c-216f.hcd failed with error -2
[    5.678853] Bluetooth: hci0: BCM: Patch brcm/BCM20702A1-0a5c-216f.hcd not found
[   10.854607] Bluetooth: RFCOMM TTY layer initialized
[   10.854613] Bluetooth: RFCOMM socket layer initialized
[   10.854619] Bluetooth: RFCOMM ver 1.11

Without having the proper firmware / patch loaded, the module won’t work, even though the TTY / socket layers know it’s present, which explains why Blueman did everything except actually connect to the headsets.

More searching suggested you must extract the firmware HEX file from the Windows driver. Feeding the Service Tag into the Dell support site, then feeding “Bluetooth” and “Windows 8.1, 64-bit” (preinstalled on the laptop) into the Drivers & Downloads tab gets you the relevant EXE file: Dell Wireless 1550/1560 Wi-Fi and Bluetooth Driver. It turns out to be a self-extracting ZIP file (in Windows, anyway), so unzip it all by yourself:

unzip Network_Driver_5DFVH_WN32_6.30.223.262_A03.EXE

This produces a blizzard of HEX files in the newly created Drivers/production/Windows8.1-x64 directory. Each firmware HEX file is keyed to the USB Product Code identifying the unique USB gadget, found with lsusb:

lsusb
… snippage …
Bus 002 Device 003: ID 0a5c:216f Broadcom Corp. BCM20702A0 Bluetooth
… snippage …

The DW1560 apparently has a USB RAM interface, with the specific HEX file identified in the CopyList stanza of the INF file corresponding to that USB Product Code:

grep -i -A 5  ramusb216f.copylist Drivers/production/Windows8.1-x64/bcbtums-win8x64-brcm.inf
[RAMUSB216F.CopyList]
bcbtums.sys
btwampfl.sys
BCM20702A1_001.002.014.1443.1572.hex
… snippage …

However, the Linux firmware loader needs a different file format with a different name, mashed together from the HEX file, USB Vendor, and USB Product codes:

hex2hcd -o BCM20702A1-0a5c-216f.hcd BCM20702A1_001.002.014.1443.1572.hex

The converted firmware file goes where the loader expected to find it:

sudo cp BCM20702A1-0a5c-216f.hcd /lib/firmware/brcm/

Whereupon next reboot sorted things out:

dmesg | grep -i blue
[    6.024838] Bluetooth: Core ver 2.22
[    6.024868] Bluetooth: HCI device and connection manager initialized
[    6.024872] Bluetooth: HCI socket layer initialized
[    6.024874] Bluetooth: L2CAP socket layer initialized
[    6.024881] Bluetooth: SCO socket layer initialized
[    6.100796] Bluetooth: BNEP (Ethernet Emulation) ver 1.3
[    6.100800] Bluetooth: BNEP filters: protocol multicast
[    6.100804] Bluetooth: BNEP socket layer initialized
[    6.157114] Bluetooth: hci0: BCM: chip id 63
[    6.158125] Bluetooth: hci0: BCM: features 0x07
[    6.176119] Bluetooth: hci0: BCM20702A
[    6.177114] Bluetooth: hci0: BCM20702A1 (001.002.014) build 0000
[    7.031228] Bluetooth: hci0: BCM20702A1 (001.002.014) build 1572
[    7.047177] Bluetooth: hci0: DW1560 Bluetooth 4.0 LE
[   13.141854] Bluetooth: RFCOMM TTY layer initialized
[   13.141865] Bluetooth: RFCOMM socket layer initialized
[   13.141872] Bluetooth: RFCOMM ver 1.11

The firmware may be in one of the myriad Bluetooth packages not installed by default, so perhaps identifying & installing the proper package would sidestep the hocus-pocus.

Maybe next time?

Now I can wear my Bose Hearphones in Zoom sessions with the E7250, because my Pixel 3a phone heats up almost to the gets-bendy level while thrashing its battery to death.