https://bugzilla.kernel.org/show_bug.cgi?id=218494 Bug ID: 218494 Summary: btrtl/rtl8761bu: RFCOMM is not working Product: Drivers Version: 2.5 Hardware: All OS: Linux Status: NEW Severity: normal Priority: P3 Component: Bluetooth Assignee: linux-bluetooth@xxxxxxxxxxxxxxx Reporter: manio@xxxxxxxxxx Regression: No Hi, I am trying to use an RFCOMM-capable dongle under Arch Linux (kernel: 6.6.10-arch1-1). The BT usb adapter is: ID 0bda:8771 Realtek Semiconductor Corp. Bluetooth Radio dmesg: [ 19.174428] Bluetooth: Core ver 2.22 [ 19.174448] NET: Registered PF_BLUETOOTH protocol family [ 19.174448] Bluetooth: HCI device and connection manager initialized [ 19.174452] Bluetooth: HCI socket layer initialized [ 19.174454] Bluetooth: L2CAP socket layer initialized [ 19.174460] Bluetooth: SCO socket layer initialized [ 20.497753] Bluetooth: hci0: RTL: examining hci_ver=0a hci_rev=000b lmp_ver=0a lmp_subver=8761 [ 20.500891] Bluetooth: hci0: RTL: rom_version status=0 version=1 [ 20.500894] Bluetooth: hci0: RTL: loading rtl_bt/rtl8761bu_fw.bin [ 20.502433] Bluetooth: hci0: RTL: loading rtl_bt/rtl8761bu_config.bin [ 20.503140] Bluetooth: hci0: RTL: cfg_sz 6, total sz 30210 [ 20.898620] Bluetooth: BNEP (Ethernet Emulation) ver 1.3 [ 20.898620] Bluetooth: BNEP filters: protocol multicast [ 20.898620] Bluetooth: BNEP socket layer initialized [ 21.285074] Bluetooth: hci0: RTL: fw version 0xdfc6d922 [ 21.430191] Bluetooth: MGMT ver 1.22 [ 40.360736] Bluetooth: RFCOMM TTY layer initialized [ 40.360743] Bluetooth: RFCOMM socket layer initialized [ 40.360746] Bluetooth: RFCOMM ver 1.11 The rfcomm utility was not provided so I had to install: https://archlinux.org/packages/extra/x86_64/bluez-deprecated-tools/ unfortunately the command: rfcomm connect 0 B8:8B:15:0A:1C:AD gives: Can't connect RFCOMM socket: Operation now in progress I tried also with `bind` argument - all of this gives errors. Finally I tried python tools to directly use RFCOMM, then even a rust rfcat tool from: https://github.com/bluez/bluer/blob/master/bluer-tools/src/rfcat.rs All gives various errors/timeouts and cannot connect to the dongle's serial port. I was also trying to pair/connect with bluetoothctl prior this - no change. In fact (see below - pairing seems not needed at all). Finally I started very very old Asus laptop with debian. I invoked: rfcomm connect 0 B8:8B:15:0A:1C:AD and this immediately gives me: Connected /dev/rfcomm0 to B8:8B:15:0A:1C:AD on channel 1 Press CTRL-C for hangup ... and it works like a charm!!! I can connect minicom and communication is working (no pairing/connecting with bluetoothctl needed). dmesg there: [ 298.641307] Bluetooth: Core ver 2.22 [ 298.641393] Bluetooth: HCI device and connection manager initialized [ 298.641405] Bluetooth: HCI socket layer initialized [ 298.641409] Bluetooth: L2CAP socket layer initialized [ 298.641419] Bluetooth: SCO socket layer initialized [ 299.673331] Bluetooth: hci0: unexpected event for opcode 0x0000 [ 311.510413] Bluetooth: BNEP (Ethernet Emulation) ver 1.3 [ 311.510422] Bluetooth: BNEP filters: protocol multicast [ 311.510435] Bluetooth: BNEP socket layer initialized [ 1902.017008] Bluetooth: RFCOMM TTY layer initialized [ 1902.017026] Bluetooth: RFCOMM socket layer initialized [ 1902.017048] Bluetooth: RFCOMM ver 1.11 the adapter is: ID 0b05:1712 ASUSTek Computer, Inc. BT-183 Bluetooth 2.0+EDR adapter I am now trying to identify the problem/difference. I've logged all data using btmon from the start to invoking the rfcom connect. I can see that the difference start when my Asus laptop is showing this: < ACL Data TX: Handle 42 flags 0x02 dlen 10 #13 [hci0] 40.891571 L2CAP: Information Request (0x0a) ident 1 len 2 Type: Extended features supported (0x0002) > HCI Event: Number of Completed Packets (0x13) plen 5 > #14 [hci0] 40.898476 Num handles: 1 Handle: 42 Address: B8:8B:15:0A:1C:AD (OUI B8-8B-15) Count: 1 > ACL Data RX: Handle 42 flags 0x02 dlen 16 > #15 [hci0] 40.899488 L2CAP: Information Response (0x0b) ident 1 len 8 Type: Extended features supported (0x0002) Result: Success (0x0000) Features: 0x00000000 < ACL Data TX: Handle 42 flags 0x02 dlen 12 #16 [hci0] 40.899554 L2CAP: Connection Request (0x02) ident 2 len 4 PSM: 3 (0x0003) Source CID: 64 I don't see any L2CAP and RFCOMM lines on the "bad" ArchLinux setup. ps. I tested the dongle also from Windows and Android - also works OK. update: I've exposed the laptop's bluetooth adapter to my ArchLinux using USB/IP method. This way on the same platform where the Realtek USB adapter is not working I was able to also use laptop's BT adapter. Here are the results: ❯ rfcomm -i hci0 connect 0 B8:8B:15:0A:1C:AD Can't connect RFCOMM socket: Operation now in progress # --> problem on realtek ❯ rfcomm -i hci1 connect 0 B8:8B:15:0A:1C:AD Connected /dev/rfcomm0 to B8:8B:15:0A:1C:AD on channel 1 Press CTRL-C for hangup ^CDisconnected # --> works great on Asus BT Conclusion: the ArchLinux platform is OK (i mean the distribution, bluetooth stack, kernel modules and utilities). The problem seems to be the Realtek drivers/firmware for my rtl8761bu... I am attaching full logs (called good and bad). dvbsnoop logs also included. update2: I also tested the initial firmware added (from 2021-06-09): https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/log/rtl_bt/rtl8761bu_fw.bin also doesn't work -- You may reply to this email to add a comment. 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