Re: [PATCH] Bluetooth: btmtk: Remove resetting mt7921 before downloading the fw

[Bitterblue Smith <rtl8821cerfe2@gmail.com>]

On 18/01/2025 18:58, John Glotzer wrote:
> (Note: additional discussion has taken place under
> Re: [REGRESSION] bluetooth: mt7921: Crash on Resume From Suspend And Hibernate)
> 
> Hi,
> 
> I have dug further into this issue and I think I have a root cause analysis that
> makes sense (at least it does for me :) ).
> The TLDR is that the root cause is the following commit that was introduced with the 6.11 kernel.
> 
> https://github.com/torvalds/linux/commit/d53ab629cff57
> 
> Furthermore, the problem must be the call to usleep_range() in
> drivers/net/wireless/mediatek/mt76/mt792x_core.c as this is the only behavioral change.
> 
> Notice that this commit first shows up in v6.11-rc1 and is present for all subsequent releases,
> which matches perfectly the breakage pattern seen by the user community.
> 
> What, then, is the evidence for this?
> 
> First of all the entire community has been unanimous in the observation that the issue
> started with the 6.11 kernel. The universal experience has been that any kernel prior
> to that had no issues, and all kernels starting with 6.11 were affected. Also no attempts
> to mitigate the issue in code by attacking the problem via the firmware download code paths have
> been fruitful.
> 
> The next piece of solid data is outlined here:
> 
> https://github.com/alimert-t/suspend-freeze-fix-for-mt7921e
> 
> Here the lead paragraph states:
> "A suspend/resume issue occurs on systems with the MediaTek MT7921 Wi-Fi adapter when
> running on Kernel 6.11.-. After suspending, the system fails to resume / freezes and requires a hard
> reset."
> 
> The mitigation for this issue has consisted of one of two approches:
> 
> - rfkill bluetooth and wifi on sleep and reverse the process on wake
> - add the parameter mt7921e.disable_aspm=y to the kernel command line
> (anecdotally I have seen reports of people doing things like turning off bluetooth
>  and/or wifi before suspending or for that matter rmmod mt7921e before suspending).
> 
> I personally have used both of these methods with a sucess rate of 100%.
> 
> The way to unlock the puzzle is to examine the 6.11 code with an eye towards
> - what changed between v6.10 and v6.11?
> - what is the intersection between this changeset and the disable_aspm paramter?
> 
> To cut to the chase the answer to both these questions is just the contents of
> https://github.com/torvalds/linux/commit/d53ab629cff57. I confirmed this by
> diffing v6.10 and v6.11 and then going through the diff looking for disable_aspm.
> 
> The following lines were added to drivers/net/wireless/mediatek/mt76/mt7921/pci.c
> 
> 	if (!mt7921_disable_aspm && mt76_pci_aspm_supported(pdev))
> 		dev->aspm_supported = true;
> 
> The bitfield aspm_supported was added to the struct mt792x_dev in drivers/net/wireless/mediatek/mt76/mt792x.h
> 
> and if this bitfield is true then the call to usleep_range is made in  __mt792xe_mcu_drv_pmctrl()
> in drivers/net/wireless/mediatek/mt76/mt792x_core.c.
> 
> 		if (dev->aspm_supported)
> 			usleep_range(2000, 3000);
> 
> By setting mt7921e.disable_aspm=y on the kernel command line, this code pathway is avoided
> and no crash or lockup happens when the device is woken back up.
> 
> Disclaimers:
> 
> - I don't claim to know the root cause for why the call to usleep_range() leads to a crash or a
>   freeze.
> 
> - I don't know the details of the specific issue the code for commit d53ab629cff57 was designed
>   to fix, hence I don't know the consequences of removing the call to usleep_range(). However,
>   I do know that the user experience has been significantly impacted negatively by the introduction
>   of d53ab629cff57 into the 6.11 kernel.
> 
> Thanks for your attention,
> 
> John Glotzer
> 
> 

John and Sergio, have y'all tried kernel 6.12.8 or newer?
People say the suspend problem is fixed:

https://bugzilla.kernel.org/show_bug.cgi?id=219514#c11