Re: [REGRESSION] USB ports do not work after suspend/resume cycle with v6.6.2

[Vlastimil Babka <vbabka@suse.cz>]

+Cc workflows

On 11/24/23 12:43, Greg Kroah-Hartman wrote:
> On Thu, Nov 23, 2023 at 07:20:46PM +0100, Oleksandr Natalenko wrote:
>> Hello.
>> 
>> Since v6.6.2 kernel release I'm experiencing a regression with regard
>> to USB ports behaviour after a suspend/resume cycle.
>> 
>> If a USB port is empty before suspending, after resuming the machine
>> the port doesn't work. After a device insertion there's no reaction in
>> the kernel log whatsoever, although I do see that the device gets
>> powered up physically. If the machine is suspended with a device
>> inserted into the USB port, the port works fine after resume.
>> 
>> This is an AMD-based machine with hci version 0x110 reported. As per
>> the changelog between v6.6.1 and v6.6.2, 603 commits were backported
>> into v6.6.2, and one of the commits was as follows:
>> 
>> $ git log --oneline v6.6.1..v6.6.2 -- drivers/usb/host/xhci-pci.c 
>> 14a51fa544225 xhci: Loosen RPM as default policy to cover for AMD xHC
>> 1.1
>> 
>> It seems that this commit explicitly enables runtime PM specifically
>> for my platform. As per dmesg:
>> 
>> v6.6.1: quirks 0x0000000000000410 v6.6.2: quirks 0x0000000200000410
>> 
>> Here, bit 33 gets set, which, as expected, corresponds to:
>> 
>> drivers/usb/host/xhci.h 1895:#define XHCI_DEFAULT_PM_RUNTIME_ALLOW
>> BIT_ULL(33)
>> 
>> This commit is backported from the upstream commit 4baf12181509, which
>> is one of 16 commits of the following series named "xhci features":
>> 
>> https://lore.kernel.org/all/20231019102924.2797346-1-mathias.nyman@linux.intel.com/
>>
>>  It appears that there was another commit in this series, also from
>> Basavaraj (in Cc), a5d6264b638e, which was not picked for v6.6.2, but
>> which stated the following:
>> 
>> Use the low-power states of the underlying platform to enable runtime
>> PM. If the platform doesn't support runtime D3, then enabling default
>> RPM will result in the controller malfunctioning, as in the case of
>> hotplug devices not being detected because of a failed interrupt
>> generation.
>> 
>> It felt like this was exactly my case. So, I've conducted two tests:
>> 
>> 1. Reverted 14a51fa544225 from v6.6.2. With this revert the USB ports
>> started to work fine, just as they did in v6.6.1. 2. Left 14a51fa544225
>> in place, but also applied upstream a5d6264b638e on top of v6.6.2. With
>> this patch added the USB ports also work after a suspend/resume cycle.
>> 
>> This runtime PM enablement did also impact my AX200 Bluetooth device,
>> resulting in long delays before headphones/speaker can connect, but
>> I've solved this with btusb.enable_autosuspend=N. I think this has
>> nothing to do with the original issue, and I'm OK with this workaround
>> unless someone has got a different idea.
>> 
>> With that, please consider either reverting 14a51fa544225 from the
>> stable kernel, or applying a5d6264b638e in addition to it. Given the
>> mainline kernel has got both of them, I'm in favour of applying
>> additional commit to the stable kernel.
> 
> I've applied this other commit as well to all of the affected branches, 
> thanks for letting us know.
> 
>> I'm also Cc'ing all the people from our Mastodon discussion where I
>> initially complained about the issue as well as about stable kernel
>> branch stability:
>> 
>> https://activitypub.natalenko.name/@oleksandr/statuses/01HFRXBYWMXF9G4KYPE3XHH0S8
>>
>>  I'm not going to expand more on that in this email, especially given
>> Greg indicated he read the conversation, but I'm open to continuing
>> this discussion as I still think that current workflow brings visible
>> issues to ordinary users, and hence some adjustments should be made.
> 
> What type of adjustments exactly?  Testing on wide ranges of systems is
> pretty hard, and this patch explicitly was set to be backported when it
> hit Linus's tree,

Are you sure about that "explicitly was set to be backported" part?
According to Documentation/process/stable-kernel-rules.rst:

> There are three options to submit a change to -stable trees:
> 
>  1. Add a 'stable tag' to the description of a patch you then submit for
>     mainline inclusion.
>  2. Ask the stable team to pick up a patch already mainlined.
>  3. Submit a patch to the stable team that is equivalent to a change already
>     mainlined.

I don't see a stable tag in 4baf12181509 ("xhci: Loosen RPM as default
policy to cover for AMD xHC 1.1"), was it option 2 or 3 then?

Do you mean the Fixes: tag? the docs only say that can replace the "# 3.3.x"
part to determine where backporting should stop, but is not itself an
explicit marking for stable backport?

> it just looks like someone forgot to mark the
> follow-up patch that you found also to be properly backported.
> 
> We will always make mistakes, we are only human.  The best thing to do
> is if we get notified quickly of issues, like you did here, and work to
> resolve them, as we have done here.  So again, thanks for letting us
> know about the problem, and be sure to let us know of any future issues
> you might find as well.
> 
> Remember, hardware is messy, and the kernel's job is to fix hardware
> issues and quirks in it.  Sometimes we get it wrong as we are trying to
> fix up inconsistencies and they cause other problems, so in the end, we
> can only grumble at the hardware companies for stuff like this, be
> patient with those of us who have to deal with this mess :)
> 
> thanks,
> 
> greg k-h