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Date: Wed, 10 Apr 2024 15:40:31 -0700
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Subject: Re: QCA6390 bluetooth doesn't work after warm boot or
 disable/reenable
From: Wren Turkal <wt@penguintechs.org>
To: Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
 Marcel Holtmann <marcel@holtmann.org>,
 Johan Hedberg <johan.hedberg@gmail.com>
Cc: ath11k@lists.infradead.org, linux-bluetooth@vger.kernel.org,
 Kalle Valo <kvalo@kernel.org>
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On 4/10/24 3:00 PM, Wren Turkal wrote:
> +Johan since he's a former BT drivers maintainer.
> 
> On 4/9/24 1:11 PM, Wren Turkal wrote:
>> On 4/9/24 1:03 PM, Luiz Augusto von Dentz wrote:
>>> 5.19 seems a little too old, imo, or has it been broken for that long,
>>> did you at least tried with bluetooth-next? Try contacting the people
>>> who actually wrote the driver.
>>
>> Sorry, I didn't answer your question. Yes, I do think it's been broken 
>> for longer than that, but I wanted to confirm.
> 
> Okay, so I tried 6.9-rc3 and every main release 5.19-6.8.
> 
> I have found the following:
> 
> * older kernels (6.3 and before) seem to be far less likely to kill on a 
> cycling the bluetooth service.
> * 6.8/6.9-rcs consistently destroy bluetooth when stopping and 
> restarting the service
> * If I destroy the bluetooth service with a BT service restart in 
> 6.9-rc3 and warm reboot into any release back to 5.19, bluetooth does 
> not work
> * cold boot works in all cases assuming I give the laptop about 5s 
> between power off/on

I just did another experiment on 6.9-rc3. I blacklisted relevant 
bluetooth modules and then warm booted without the blacklist. I did this 
for both the "bluetooth" and "btqca" modules. In both cases, I cold 
booted with and appropriate "module_blacklist" kernel arg. After the 
boot, I verified the module was not loaded. I then warm booted without 
the blacklist, and the bluetooth works, so bluetooth only seems to fail 
when the linux module code for closing the device is run before a warm boot.

> So, I suspsect that the process of closing out the hardware may be 
> leaving it in a state that the reset cannot handle (and probably never 
> could handle).
> 
> I also found that qualcomm has docs here: 
> https://www.qualcomm.com/products/technology/wi-fi/fastconnect/fastconnect-6800#Documentation
> 
> However, I am not a member of a Qualcomm verified company (mentioned in 
> the doc links). Luiz, Marcel, or Johan, do you have any contacts that 
> might be able to help me in getting info about the technical docs for 
> this hardware? I would love to see if I can find any issues in how the 
> hardware is being reset.
> 
> As an independent dev, I don't even know what it takes to get that kind 
> of access. I would welcome any help here. Hey Qualcomm, are you hiring? :P
> 
> wt

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