[Bug 2076407] Re: Title: Bluetooth 5.4 Adapter (Ugreen CM749) Not Functioning on Ubuntu 20.04 with Kernel 6.x Description: The Bluetooth 5.4 adapter Ugreen CM749 is not functioning on Ubuntu 20.04 with Kernel 6.x. The adapter is detected by the system but fails to initialize, showing a "Connection timed out (110)" error when attempting to bring up the interface. The Bluetooth 5.0 dongle works without issues on the same system. Steps to Reproduce: 1. Plugged in the Ugreen CM749 Bluetooth 5.4 adapter. 2. Ran `hciconfig hci0 up` to bring up the Bluetooth interface. 3. Observed the error "Connection timed out (110)" in the terminal. 4. Checked the dmesg logs and found repeated Bluetooth errors. Expected Behavior: The Bluetooth 5.4 adapter should initialize correctly, allowing for Bluetooth functionality such as pairing and connecting devices. Actual Behavior: The Bluetooth 5.4 adapter fails to initialize, with the interface staying down and connection attempts timing out. A dditional Information: - Kernel Version: 6.10.2-061002-generic - Ubuntu Version: 20.04 - Hardware Information: *-network:1 description: Bluetooth device product: Realtek Bluetooth Adapter vendor: Realtek Semiconductor Co., Ltd. physical id: 0 bus info: usb@1:1 version: 1.00 - dmesg Output: [12345.6789] Bluetooth: hci0: Opcode 0x1005 failed: -110 - hciconfig Output: hci0: Type: Primary Bus: USB BD Address: 00:A7:45:28:00:B3 ACL MTU: 0:0 SCO MTU: 0:0 DOWN RX bytes:171 acl:0 sco:0 events:10 errors:0 TX bytes:276 acl:0 sco:0 commands:11 errors:0

Sun, 27 Jul 2025 18:50:49 -0700

That's great, I also have modified a version of the kernel myself
(version 6.15) very much like you did, but I achieve it by compiling
from source code downloaded from the official page. The problem is that
I'm afraid of installing it in my main machine because I'm not
experienced in kernel customization and can't afford to break it right
now, not even for a bit, so I'm still waiting for an official release. I
have also contacted the Ugreen support (the manufacturer) for
clarification over the similarity of those models CM748 and CM749, they
have pretty much the same requisites in terms of drivers as far as I was
able to obtain from them, hence they can problably can share this
solution without further problems (vindicating what you have pointed).

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Title:
  Title: Bluetooth 5.4 Adapter (Ugreen CM749) Not Functioning on Ubuntu
  20.04 with Kernel 6.x  Description: The Bluetooth 5.4 adapter Ugreen
  CM749 is not functioning on Ubuntu 20.04 with Kernel 6.x. The adapter
  is detected by the system but fails to initialize, showing a
  "Connection timed out (110)" error when attempting to bring up the
  interface. The Bluetooth 5.0 dongle works without issues on the same
  system.  Steps to Reproduce: 1. Plugged in the Ugreen CM749 Bluetooth
  5.4 adapter. 2. Ran `hciconfig hci0 up` to bring up the Bluetooth
  interface. 3. Observed the error "Connection timed out (110)" in the
  terminal. 4. Checked the dmesg logs and found repeated Bluetooth
  errors.  Expected Behavior: The Bluetooth 5.4 adapter should
  initialize correctly, allowing for Bluetooth functionality such as
  pairing and connecting devices.  Actual Behavior: The Bluetooth 5.4
  adapter fails to initialize, with the interface staying down and
  connection attempts timing out.  Additional Information: - Kernel
  Version: 6.10.2-061002-generic - Ubuntu Version: 20.04 - Hardware
  Information:   *-network:1        description: Bluetooth device
  product: Realtek Bluetooth Adapter        vendor: Realtek
  Semiconductor Co., Ltd.        physical id: 0        bus info: usb@1:1
  version: 1.00 - dmesg Output:   [12345.6789] Bluetooth: hci0: Opcode
  0x1005 failed: -110 - hciconfig Output:   hci0: Type: Primary Bus: USB
  BD Address: 00:A7:45:28:00:B3 ACL MTU: 0:0 SCO MTU: 0:0   DOWN   RX
  bytes:171 acl:0 sco:0 events:10 errors:0   TX bytes:276 acl:0 sco:0
  commands:11 errors:0

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