[Bug 221837] New: Bluetooth (RTL8852BU, 0bda:b853) never initializes. Opcode 0xfcf0

https://bugzilla.kernel.org/show_bug.cgi?id=221837

            Bug ID: 221837
           Summary: Bluetooth (RTL8852BU, 0bda:b853) never initializes.
                    Opcode 0xfcf0
           Product: Drivers
           Version: 2.5
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: blocking
          Priority: P3
         Component: Bluetooth
          Assignee: [email protected]
          Reporter: [email protected]
        Regression: No

## System information
- Distro: Linux Mint 22.3 (zena), Ubuntu 24.04 base
- Kernel: 6.11.0-17-generic (#17~24.04.2-Ubuntu SMP PREEMPT_DYNAMIC)
- linux-firmware package: 20240318.git3b128b60-0ubuntu2.27
- Laptop: Lenovo LOQ 15AHP11
- Bluetooth controller: Realtek RTL8852BU, USB ID 0bda:b853 (Bus 001 Device
004)
- WiFi: Realtek RTL8852BE, PCI ID 10ec:b852, driver rtw89_8852be

## Problem
hci0 never comes up. BD Address stays 00:00:00:00:00:00, state DOWN,
`bluetoothctl show` reports "No default controller available". Reproduces on
every boot.

## dmesg (current state, after updating rtl8852bu_fw.bin)
```
[    2.491778] Bluetooth: hci0: RTL: examining hci_ver=0b hci_rev=000b
lmp_ver=0b lmp_subver=8852
[    2.494811] Bluetooth: hci0: RTL: rom_version status=0 version=3
[    2.494818] Bluetooth: hci0: RTL: loading rtl_bt/rtl8852bu_fw.bin
[    2.495778] Bluetooth: hci0: RTL: loading rtl_bt/rtl8852bu_config.bin
[    2.503791] Bluetooth: hci0: Opcode 0xfcf0 failed: -16
[    2.507788] Bluetooth: hci0: AOSP extensions version v0.96
[    2.507793] Bluetooth: hci0: AOSP quality report is not supported
```

## What I've tried

1. Confirmed rfkill is not blocking (`Soft blocked: no`, `Hard blocked: no` for
both `ideapad_bluetooth` and `hci0`).
2. Confirmed Bluetooth works fine from Windows on the same physical hardware
(dual-boot). (fast-boot is disabled)
3. The distro-packaged `rtl8852bu_fw.bin` (linux-firmware 20240318 snapshot)
additionally logged `Bluetooth: hci0: RTL: didn't find patch for chip id 3`
before the Opcode failure i.e. this chip's rom_version (2, reported as "chip id
3") had no matching entry in that firmware build's internal patch table.
4. Replaced `/usr/lib/firmware/rtl_bt/rtl8852bu_fw.bin` with the current
upstream linux-firmware HEAD build (fetched from git.kernel.org, 129733 bytes,
md5 c97273d1bf9a715c46e4fc73eb0283b3, valid `RTBTCore` header). This resolved
the "didn't find patch" message but `Opcode 0xfcf0 failed: -16` still occurs
immediately after.
5. Confirmed via linux-firmware's WHENCE manifest that
`rtl_bt/rtl8852bu_config.bin -> rtl8761bu_config.bin` is the correct,
intentional upstream mapping — ruled out using the wrong config file.
6. Full reboot
7. Attempted to isolate a WiFi/Bluetooth coexistence conflict (RTL8852B is a
combo WiFi+BT chip) by unloading the rtw89 WiFi stack before reloading btusb.
`rtw89_8852be`/`rtw89_8852b`/`rtw89_8852b_common` unloaded, but
`rtw89_pci`/`rtw89_core` stayed loaded (rmmod dependency-order limitation).
8. Set `usbcore.autosuspend=-1` as a kernel boot parameter.

The firmware's patch table now recognizes this chip's rom_version, but the
controller still returns "Command Disallowed" on the vendor download-config
opcode 0xfcf0. This looks like it needs additional handling in btrtl.c/btusb.c
for this specific RTL8852BU chip stepping (rom_version=2). Is there a known
driver-side fix in progress, or would a btmon/HCI trace help narrow this down
further?

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