RE: rtl_bt: RTL8852BU rom_version 3 has no matching in rtl8852bu_fw.bin

[Hilda Wu <hildawu@realtek.com>]

Hi Deniz,

Thank you for the detailed analysis and the parser trace — it clearly pinpoints the issue.

Root cause:
The RTL8852BU eco version 4 variant on this device is currently not yet supported in the released firmware. The existing firmware does not cover this eco version, which is why the kernel parser cannot find a matching image and returns -ENODATA.

Current status:
Firmware support for eco 4 is currently in preparation and is targeted for release by end of November 2026. Once available, it will be submitted to linux-firmware accordingly.

In the meantime, if you'd like to test early with a pre-release firmware binary, we are happy to provide one — your validation feedback would be very much appreciated.

We also agree with your suggestion to improve the error message in btrtl_parse_section() to make this kind of failure easier to diagnose. We'll follow up with a separate patch for that.

Sorry for the wait, and thank you again for the thorough investigation.

Best regards,
Hilda

-----Original Message-----
From: deniz <denizgu@protonmail.ch> 
Sent: Sunday, August 2, 2026 8:31 PM
To: Hilda Wu <hildawu@realtek.com>; Ping-Ke Shih <pkshih@realtek.com>; Timlee <timlee@realtek.com>; Zong-Zhe Yang <kevin_yang@realtek.com>; linux-bluetooth@vger.kernel.org
Subject: rtl_bt: RTL8852BU rom_version 3 has no matching in rtl8852bu_fw.bin


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Hello there, forwarding this report to people in the linux-firmware repo working on realtek devices.

A similar report was filed here: https://lore.kernel.org/linux-firmware/CAP9emj2-8hXB3t3SFD6RU2ZsttsiOtJ6W4Bto4jXSw+dB==TmA@mail.gmail.com It looks to be a widespread problem.

The current rtl_bt/rtl8852bu_fw.bin (Release Version 0x127C_FD78, commit"rtl_bt: Update RTL8852B BT USB FW to 0x127C_FD78", 2026-03-26) contains no firmware patch matching the ECO revision of the RTL8852BU controller in Lenovo IdeaPads shipping today. Bluetooth is completely non-functional as a result.

Could an rom version 3 (eco 4) patch be added for RTL8852B BT USB?

I have provided diagnostic details below, please feel free to reach out for more.

Happy to test any candidate firmware and report back.
Thanks,

Deniz


-------Hardware--------------


  Machine         : Lenovo IdeaPad  BT controller   : 0bda:b853 "Bluetooth Radio", Realtek (USB)
  WiFi (same M.2) : RTL8852BE, rtw89_8852be, PCIe 01:00.0 - works normally
  Driver          : btusb + btrtl
  linux-firmware  : linux-firmware-realtek 20260622-1 (Arch Linux)

Controller reports:
  Bluetooth: hci0: RTL: examining hci_ver=0b hci_rev=000b lmp_ver=0b lmp_subver=8852
  Bluetooth: hci0: RTL: rom_version status=0 version=3
  Bluetooth: hci0: RTL: btrtl_initialize: key id 0

This matches the intended IC table entry in drivers/bluetooth/btrtl.c, so the correct firmware file is being selected:

  { IC_INFO(RTL_ROM_LMP_8852A, 0xb, 0xb, HCI_USB),
    .config_needed = false,
    .has_rom_version = true,
    .has_msft_ext = true,
    .fw_name  = "rtl_bt/rtl8852bu_fw",
    .cfg_name = "rtl_bt/rtl8852bu_config",
    .hw_info  = "rtl8852bu" },


-------Problem-------

btrtl_parse_section() accepts only subsections whose ECO revision matches the
controller:

  /* drivers/bluetooth/btrtl.c */
  if (common_subsec->eco != btrtl_dev->rom_version + 1)
          continue;

The controller reports rom_version = 3, so only an eco 4 patch is accepted.
Parsing the shipped firmware with an exact replica of the kernel parser gives:

  fw_len       : 129733
  signature    : RTBTCore          (RTL_EPATCH_SIGNATURE_V2)
  num_sections : 2

  section[0]: opcode=0x01 (RTL_PATCH_SNIPPETS) len=129686
      section_hdr.num = 2 subsections
      [ 0] skip   eco=0x01 prio=15 len=67133    eco 1 != rom_version+1 (4)
      [ 1] skip   eco=0x02 prio=15 len=62533    eco 2 != rom_version+1 (4)
      -> contributed 0 bytes
  section[1]: opcode=0x08 (not handled by the switch) len=0
      -> contributed 0 bytes

  total len accumulated = 0

Only eco 1 and eco 2 are present; eco 3 is absent as well. Both subsections are skipped, so no patch data is collected.

I also downloaded rtl_bt/rtl8852bu_fw.bin directly from upstream linux-firmware and confirmed it is byte-identical to the packaged copy, so this is not a distribution packaging artifact:


------- Consequence -------

With zero bytes collected, rtlbt_parse_firmware_v2() returns -ENODATA, no firmware is downloaded to the controller, btrtl_setup_realtek() fails, and hci_dev_open() fails. HCI_SETUP is therefore never cleared and mgmt_index_added() never fires, so bluetoothd never sees a controller at all:

  $ bluetoothctl list                 # empty
  $ sudo btmgmt info
  Index list with 0 items
  $ sudo btmgmt config
  Unconfigured index list with 0 items

The controller itself responds correctly from stock ROM firmware. btmon shows every identification and setup command succeeding - vendor 0xfc61 (twice), Read Local Version Information, vendor 0xfc6d, MSFT Read Supported Features, and the AOSP vendor command 0xfd53 all return Status: Success. The only command that does not is the MSFT LE Set Advertisement Filter Enable, which returns Command Disallowed (0x0c) - expected, given no patch firmware was ever loaded.

Reproduced identically on kernels 6.18.40-2-lts and 7.1.4-arch1-1.

------- Note on diagnosability -------

Both error paths involved are silent, which made this very hard to track down:

  rtlbt_parse_firmware_v2():   if (!len) return -ENODATA;   /* no message */
  btrtl_setup_rtl8723b():      if (ret < 0) goto out;       /* no message */

The only kernel output is the firmware being loaded from disk, followed by nothing at all - no download, no error. A single rtl_dev_err() naming the required versus available ECO revisions would make this diagnosable in seconds. I am happy to send a separate patch for that to linux-bluetooth if useful.


------- ECO coverage across the family -------

For reference, ECO revisions present in linux-firmware-realtek 20260622-1:

  rtl8852au_fw.bin      eco 2
  rtl8852bu_fw.bin      eco 1, 2      <- this machine needs eco 4
  rtl8852btu_fw.bin     eco 1
  rtl8852cu_fw_v2.bin   eco 1, 2
  rtl8851bu_fw.bin      eco 1
  rtl8922au_fw.bin      eco 2