Linux: Atheros QCA6174′s Bluetooth disappearing after reboot

When Bluetooth goes poof

Having rebooted my computer after a few months of continuous operation, I suddenly failed to use my Bluetooth headphones. It took some time to figure out that the problem wasn’t with the Cinnamon 3.8.9 fancy stuff, nor the DBus interface, which produced error messages. There was simply no Bluetooth device in the system to talk to.

Prior to this mishap, my Atheros QCA6174 had worked flawlessly and reliably for several months, both as a Wifi adapter and a Bluetooth adapter.

For the record, I have a Linux Mint 19 Tara machine with 4.15.0-20-generic kernel on a X299 AORUS Gaming 7 motherboard, running in 64 bit mode of course.

I’ll jump to the spoiler: If you happen to have a Qualcomm Atheros QCA6174 802.11ac Wireless Network Adapter on your machine, never just reboot the machine: Shut down the computer completely, and disconnect main power for a minute or so with the power supply’s switch. Just powering off the computer the fine way isn’t enough. The device probably continues to get power from the motherboard when in computer is off by virtue of its own power control.

Powering off the computer this way is what solved it for me. However there are also some rumors on the web, which I can’t confirm, about Bluetooth coming back to life after loading Windows on the same computer. Or turning Bluetooth off and on again with the BIOS. My guess is that due to a bug, the chip sometimes needs some kind of tickle on shutdown or when starting, or Bluetooth is lost. Something that is worked around with a hush-hush fix in the driver for Windows, but the Linux driver doesn’t do the same.

This post goes down to the gory details, partly for the sake of quick diagnostics in the future, and partly because Bluetooth tends to be a mystery thing. So I’m trying to give an idea on what’s going on.

Why it’s confusing

Here’s the thing: The Qualcomm QCA6174 connects to the motherboard as a PCIe device as a Wifi adapter, and to the USB bus as a Bluetooth device. Sounds weird, but that’s the way it is. Bluetooth has been wonky for 20 years, and that’s probably its destiny.

So there are wires going from the QCA6174 to the PCIe bus and other wires from the same device going to one of the ports of the motherboard’s USB root hub (see details below). On my specific motherboard, the Bluetooth interface of the QCA6174 is connected to port 13 of the root hub, that facilitates the motherboard’s physical USB connector at the back of the computer. So while designing the board, they wired some of the D+/D- wires to the physical ports at the back, and a couple of those go to the QCA6174. I’m saying this over and over again, because it’s so counterintuitive.

Counterintuituve, but it seems like it’s quite common. Intel’s AC 7260 Wifi / Bluetooth combo seems to do exactly the same thing.

As a PCIe device, QCA6174 has Vendor / Product IDs 168c:003e. As as USB device, it’s 0cf3:e300. Confusing? It won’t surprise me if the Wifi and Bluetooth interfaces are two independent units on the same chip, that happen to share an antenna.

Apparently, when the QCA6174 has a bad day, the PCIe interface wakes up properly, and USB doesn’t. The result is that the Wifi works fine, but the Bluetooth is absent.

To add some confusion, the kernel source’s drivers/net/wireless/ath/ath10k/usb.c matches USB device 13b1:0042, which is indeed a Linksys device (the comment in the code says Linksys WUSB6100M). Not clear why it’s there.

On the other hand, drivers/bluetooth/btusb.c, matches a whole range of Atheros USB devices, among others 0cf3:e300, calling it “QCA ROME” in the comments. So it’s the btusb module that takes care of QCA6174′s Bluetooth interface, not anything in ath/ath10k. Cute, isn’t it?

What it looks like when it works

When trying to figure out what’s wrong, it helps knowing that it looks like when it’s OK. So below is a lot of info that was collected when I got the Bluetooth up and running.

When it failed, everything looked exactly the same in relation to the device’s PCIe interface, but there was absolutely nothing related to USB and Bluetooth: No entry for the device in lsusb, hcicontrol nor rfkill, as shown below.

Kernel log output on behalf of the device, as connected to the PCIe bus. Note that the exact same logs appeared when the Bluetooth device was absent. Exactly-exactly. Down to the single character, I’ve compared them. So this isn’t really relevant, but anyhow:

[    0.126428] pci 0000:03:00.0: [168c:003e] type 00 class 0x028000
[    0.126456] pci 0000:03:00.0: reg 0x10: [mem 0x92800000-0x929fffff 64bit]
[    0.126555] pci 0000:03:00.0: PME# supported from D0 D3hot D3cold

[ ... ]

[   17.616738] ath10k_pci 0000:03:00.0: enabling device (0000 -> 0002)
[   17.617514] ath10k_pci 0000:03:00.0: pci irq msi oper_irq_mode 2 irq_mode 0 reset_mode 0

[ ... ]

[   17.915091] ath10k_pci 0000:03:00.0: Direct firmware load for ath10k/pre-cal-pci-0000:03:00.0.bin failed with error -2
[   17.915109] ath10k_pci 0000:03:00.0: Direct firmware load for ath10k/cal-pci-0000:03:00.0.bin failed with error -2
[   17.926172] ath10k_pci 0000:03:00.0: qca6174 hw3.2 target 0x05030000 chip_id 0x00340aff sub 1a56:1535
[   17.926173] ath10k_pci 0000:03:00.0: kconfig debug 0 debugfs 1 tracing 1 dfs 0 testmode 0
[   17.926505] ath10k_pci 0000:03:00.0: firmware ver WLAN.RM.4.4.1-00124-QCARMSWPZ-1 api 6 features wowlan,ignore-otp crc32 d8fe1bac
[   18.078191] ath10k_pci 0000:03:00.0: board_file api 2 bmi_id N/A crc32 506ce037

[ ... ]

[   18.642461] ath10k_pci 0000:03:00.0: Unknown eventid: 3
[   18.658195] ath10k_pci 0000:03:00.0: Unknown eventid: 118809
[   18.661096] ath10k_pci 0000:03:00.0: Unknown eventid: 90118
[   18.661772] ath10k_pci 0000:03:00.0: htt-ver 3.56 wmi-op 4 htt-op 3 cal otp max-sta 32 raw 0 hwcrypto 1

Note that two attempts to load firmware failed, but apparently the third went OK. Don’t let these error messages mislead you: The kernel messages in this respect were the same when the Bluetooth appeared and when it didn’t.

The “Unknown eventid” may appear more than once.

Its entry with plain lspci (unrelated entries removed):

$ lspci
03:00.0 Network controller: Qualcomm Atheros QCA6174 802.11ac Wireless Network Adapter (rev 32)

And now to the parts that were missing completely when the Bluetooth device didn’t appear: The logs on behalf of the device, connected to the USB bus:

[    3.764868] usb 1-13: new full-speed USB device number 12 using xhci_hcd
[    3.913930] usb 1-13: New USB device found, idVendor=0cf3, idProduct=e300
[    3.915610] usb 1-13: New USB device strings: Mfr=0, Product=0, SerialNumber=0

Plain lsusb:

$ lsusb
[ ... ]
Bus 001 Device 012: ID 0cf3:e300 Atheros Communications, Inc.
[ ... ]

lsusb, tree view (a lot of irrelevant stuff excluded):

$ lsusb -t
/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/16p, 480M
    |__ Port 13: Dev 12, If 1, Class=Wireless, Driver=btusb, 12M
    |__ Port 13: Dev 12, If 0, Class=Wireless, Driver=btusb, 12M

More in detail for the device:

# lsusb -v -d 0cf3:e300

Bus 001 Device 012: ID 0cf3:e300 Atheros Communications, Inc.
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.01
  bDeviceClass          224 Wireless
  bDeviceSubClass         1 Radio Frequency
  bDeviceProtocol         1 Bluetooth
  bMaxPacketSize0        64
  idVendor           0x0cf3 Atheros Communications, Inc.
  idProduct          0xe300
[ ... ]

Several modules appear in lsmod, but the point is that there are dependencies on bluetooth module, in particular the btusb module. Irrelevant modules deleted from list below:

$ lsusb
rfcomm                 77824  16
bnep                   20480  2
btusb                  45056  0
btrtl                  16384  1 btusb
btbcm                  16384  1 btusb
btintel                16384  1 btusb
bluetooth             548864  43 btrtl,btintel,bnep,btbcm,rfcomm,btusb

How to check if a Bluetooth device is present

There is no device file for Bluetooth interface, exactly as there’s none for network. Like there’s eth0 for Ethernet, there’s hci0 for Bluetooth.

hcicontrol grabs the info by opening a socket. As in the relevant strace:

socket(PF_BLUETOOTH, SOCK_RAW, 1)

So this is what it looked like with the Bluetooth device present (without it, hciconfig simply prints nothing):

$ hciconfig
hci0:	Type: Primary  Bus: USB
	BD Address: xx:xx:xx:xx:xx:xx  ACL MTU: 1024:8  SCO MTU: 50:8
	UP RUNNING PSCAN ISCAN
	RX bytes:1386 acl:0 sco:0 events:94 errors:0
	TX bytes:5494 acl:0 sco:0 commands:94 errors:0

Real hex numbers appear instead of the xx’s above. Use hciconfig -a for more verbose output.

And the device appears in the rfkill list, and shouldn’t be blocked.

$ rfkill list
0: hci0: Bluetooth
	Soft blocked: no
	Hard blocked: no
1: phy0: Wireless LAN
	Soft blocked: no
	Hard blocked: no

These two show that the kernel supplies a Bluetooth device to the higher software levels. If Bluetooth doesn’t work, there are other reasons…