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[2003:fc:df06:7400:6598:1d43:be65:c503]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49e71e300f3sm216791875e9.7.2026.09.14.04.44.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 14 Sep 2026 04:44:11 -0700 (PDT) Message-ID: <9ac1c05b-e9f2-49e9-af63-9cd0e42115fc@gmail.com> Date: Mon, 14 Sep 2026 13:44:10 +0200 Precedence: bulk X-Mailing-List: regressions@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Betterbird (Linux) Content-Language: en-GB, de-DE To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , Sasha Levin , Christoph Zwerschke , Max Chou , Luiz Augusto von Dentz , Marcel Holtmann , linux-bluetooth@vger.kernel.org, regressions@lists.linux.dev From: "ra.prism" Subject: [REGRESSION] btusb: ASUS USB-BT540/BT600 IDs backported without, RTL8761CUV support, adapter re-enumerates endlessly (6.18.50, 6.12.109,, 6.1.188, 5.15.221, 5.10.270) Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Hi, two btusb device-ID commits were backported to stable branches that lack the btrtl support they depend on:   980084de4d9b ("Bluetooth: btusb: Add ASUS USB-BT540 for Realtek 8761CU")   6f0624b4427e ("Bluetooth: btusb: Add ASUS USB-BT600 for Realtek 8761CU") Both set BTUSB_REALTEK for 0b05:1bef / 0b05:1d70, so the adapters now go through btrtl setup. btrtl only learned about this chip in v6.19-rc1:   4a23ce935f74 ("Bluetooth: btrtl: Add the support for RTL8761CUV") Without it, setup fails and the adapter resets in a loop. Before the backport the adapter bound via the generic Bluetooth class and did not loop. Affected, checked against the stable trees (btusb.c has 0x0b05/0x1bef, btrtl.c has no rtl8761cu entry):   released  6.18.50 (aa7b93fe98ba, bce588b4ca08), still in 6.18.51             6.12.109 (f05baf6e0680, 32412aff8d11)             6.1.188, 5.15.221, 5.10.270   queued    queue-6.6 Not affected: 7.1.y (has 4a23ce935f74 but not the IDs) and 7.2.y (has both). Observed with an ASUS USB-BT540 (0b05:1bef, hci_rev 000e, lmp_subver 8761) on 6.18.50: 203 re-enumerations in 37 minutes, one every ~10.8 s, independent of the USB port:   [    8.008281] Bluetooth: hci0: RTL: examining hci_ver=0d hci_rev=000e lmp_ver=0d lmp_subver=8761   [    8.008294] usb 5-2: USB disconnect, device number 3   [   18.476022] Bluetooth: hci0: RTL: RTL: Read reg16 failed (-110)   [   18.852034] usb 5-2: New USB device found, idVendor=0b05, idProduct=1bef, bcdDevice= 2.00   [   18.875711] Bluetooth: hci0: RTL: examining hci_ver=0d hci_rev=000e lmp_ver=0d lmp_subver=8761   [   18.886986] usb 5-2: USB disconnect, device number 4   [   29.228274] Bluetooth: hci0: RTL: RTL: Read reg16 failed (-110) Same machine and adapter on 7.2.5, which has both commits, works:   [    7.816015] Bluetooth: hci0: RTL: examining hci_ver=0d hci_rev=000e lmp_ver=0d lmp_subver=8761   [    7.820005] Bluetooth: hci0: RTL: rom_version status=0 version=1   [    7.825030] Bluetooth: hci0: RTL: loading rtl_bt/rtl8761cu_fw.bin   [    7.826003] Bluetooth: hci0: RTL: loading rtl_bt/rtl8761cu_config.bin   [    7.840001] Bluetooth: hci0: RTL: fw version 0x7bf15762 6.18.48 (without the IDs) did not loop. The kernels were distribution builds (CachyOS linux-cachyos-lts 6.18.50, linux-cachyos 7.2.5). I checked the relevant btusb/btrtl lines against the vanilla stable trees listed above. I only have the BT540 and only tested 6.18.y; the BT600 and the other branches are untested but in the same situation. Could you please:   - drop both patches from queue-6.6, and   - revert them in 6.18.y, 6.12.y, 6.1.y, 5.15.y and 5.10.y, or backport     4a23ce935f74 (btrtl.c, +15/-1) where it applies. I have not checked     whether it applies cleanly to any of these trees. Thanks, Ralf Ahlbrink #regzbot introduced: v6.18.49..v6.18.50 #regzbot title: btusb: ASUS USB-BT540/BT600 IDs in stable without RTL8761CUV btrtl support cause endless re-enumeration