* RE: rtl_bt: RTL8852BU rom_version 3 has no matching in rtl8852bu_fw.bin
2026-08-02 12:31 rtl_bt: RTL8852BU rom_version 3 has no matching in rtl8852bu_fw.bin deniz
@ 2026-08-14 11:13 ` Hilda Wu
0 siblings, 0 replies; 2+ messages in thread
From: Hilda Wu @ 2026-08-14 11:13 UTC (permalink / raw)
To: deniz, Ping-Ke Shih, Timlee, Zong-Zhe Yang,
linux-bluetooth@vger.kernel.org
Cc: Max Chou, alex_lu@realsil.com.cn, zoey_zhou,
陳泓叡
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
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