[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)

["ra.prism" <ra.prism@gmail.com>]

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