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Date:   Tue, 1 Mar 2022 09:26:45 +0000
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Subject: Re: bug kernel 5.17, qualcom and intel adapters, unable to reliably
 connect to bluetooth devices
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To:     Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Cc:     Chris Murphy <lists@colorremedies.com>,
        Bluetooth <linux-bluetooth@vger.kernel.org>,
        regressions@lists.linux.dev
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From:   Chris Clayton <chris2553@googlemail.com>
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Hi Luiz,

I guess you are hoping for PEBKAC :-)

On 28/02/2022 21:20, Luiz Augusto von Dentz wrote:
> Hi Chris,
> 
> On Mon, Feb 28, 2022 at 1:02 PM Chris Clayton <chris2553@googlemail.com> wrote:
>>
>> Hi Luiz,
>>
>> On 28/02/2022 19:34, Luiz Augusto von Dentz wrote:
>>> Hi Chris,
>>>
>>> On Sat, Feb 26, 2022 at 12:04 AM Chris Clayton <chris2553@googlemail.com> wrote:
>>>>
>>>> Hi,
>>>>
>>>> On 24/02/2022 15:16, Luiz Augusto von Dentz wrote:
>>>>>> I'll try another bisection today, but limit its range to changes made in the net/bluetooth directory.
>>>>
>>>> That  bisection has proved very difficult because the bluetooth "service" in kernels at some steps of the bisection were
>>>> completely borked to the extent that blueman's device-manager application wouldn't start and emitted the messages:
>>>>
>>>> blueman-manager 12.00.37 ERROR    Manager:137 on_dbus_name_appeared: Default adapter not found, trying first available.
>>>> blueman-manager 12.00.37 ERROR    Manager:141 on_dbus_name_appeared: No adapter(s) found, exiting
>>>>
>>>> Obviously, I don't know whether the problem I am trying to pinpoint is hiding behind this more fundamental problem with
>>>> the bluetooth "service", so being unable to say whether that kernel was good or bad, I had to skip. There seems to be a
>>>> batch of commits that mean that, whilst the kernel builds okay, hunting down a bluetooth-related problem is not
>>>> possible. Eventually and I cursed and gave up. Whatever was causing this breakage has obviously been fixed.
>>>>
>>>>> Please record the HCI with btmon, it must be producing something since
>>>>> it records even the mgmt commands.
>>>>>
>>>>
>>>> Refreshed by a good night's sleep, I started another bisection (between 5.16 and 5.17-rc1) yesterday morning but this
>>>> time did not limit it to net/bluetooth.  That was going okay until I ran into what I assume is the same batch of borked
>>>> kernels. I've been more persistent this time but have just had a run of 16 steps in which the bluetooth support in the
>>>> kernel is broken so badly that testing bluetooth is not possible. I will push on today, but I've suspended that activity
>>>> to get the hci trace that Luiz has asked for.
>>>>
>>>> Using information from the bisect, I built a kernel that had tested as bad (but not borked). The commit is
>>>> f2b551fad8d8f2ac5e1f810ad595298381e0b0c5. As I've mentioned before, the problem with devices not connecting is
>>>> intermittent - for a given kernel, sometimes a connection works and other times it doesn't. On the first boot of this
>>>> kernel, my bluetooth devices could connect, Attached are 4 files related to this - the output from btmon, and the
>>>> related portions of daemon.log, kern.log and sys.log from /var/log/. Each of the these files is suffixed with ".good".
>>>>
>>>> I then powered down the laptop and booted into the same kernel. This time the bluetooth devices could not connect. Four
>>>> more files are attached for this boot and are suffixed with ".bad". I said in an earlier email that when connection
>>>> fails, there is no output from btmon, so that log is empty. That's still the case, but I guess that fact itself is a
>>>> clue to what the problem might be. What I can add, however, is that if, in that same bad kernel, I unload and then
>>>> reload the btusb module, connections start to work. Maybe that too is a clue. The same unload/load process revives
>>>> bluetooth on a kernel built after a pull of Linus' latest and greatest this morning.
>>>>
>>>> Since I now have a workround, I'm going stop the current bisection that I was doing.  I've done another couple of steps
>>>> this morning and both produced kernels on which I could not test bluetooth and had to tell git bisect to skip. If
>>>> however, I can provide any other diagnostics, please let me know.
>>>>
>>>> Chris
>>>
>>> Can you try with the following patch:
>>>
>>> https://patchwork.kernel.org/project/bluetooth/patch/20220228173918.524733-1-brian.gix@intel.com/
>>>
>>>
>> Sorry, that patch has made no difference. After the first boot my headphones connected okay, but after a power-down and
>> reboot they would not connect without an unload and reload of the btusb module.
> 
> Can you tell us exactly what steps you are using? Are you applying on
> top of what, rc6?
> 

Until I got your patch yesterday, I was using a clone of
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git which I update frequently and have been doing so for as
long as I can remember. Just in case there was a hidden flaw in that tree, I took a new clone yesterday, (so yes, the
patch was tested on top of rc6) copied over the .config file and applied the patch. Then I built and installed the
kernel, updated grub, powered off the laptop and booted into the new kernel. Once the laptop had booted and logged in to
my LXQt desktop, I powered on my headphones and a connection was establisehed almost straight away. I powered the
headphones off and the disconnection worked fine.

Knowing that the problem crops up intermittently, I then rebooted the laptop. When the boot was complete, I then powered
on my bluetooth headphones an waited for them to connect to the laptop. After about 20 seconds, a connection had not
been established. I powered off the headphones, used modprobe to unload and then reload the btusb module. When I powered
on the headphones, a connectiin was established within 2 or 3 seconds.

I've booted this laptop countless times over the last few days. Doing the bisect, I didn't mark a commit as good until I
had done five boots and been able to connect my headphones on each boot. What I can say from that work is that two
consecutive boots into a working kernel are very rare. I can't remeber an occasion when it took more than two boots to
establish that a kernel was bad.

Chris