Date:	Thu, 26 Nov 2015 15:28:39 +0200
From:	Mathias Nyman <mathias.nyman@...el.com>
To:	Alan Stern <stern@...land.harvard.edu>,
	Daniel J Blueman <daniel@...ra.org>
CC:	USB list <linux-usb@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [4.3] kworker busy in pm_runtime_work

On 25.11.2015 17:42, Alan Stern wrote:
> On Wed, 25 Nov 2015, Daniel J Blueman wrote:
>
>> On 23 November 2015 at 23:52, Alan Stern <stern@...land.harvard.edu> wrote:
>>> On Sun, 22 Nov 2015, Daniel J Blueman wrote:
>>>
>>>> On 16 November 2015 at 23:22, Alan Stern <stern@...land.harvard.edu> wrote:
>>>>> On Mon, 16 Nov 2015, Daniel J Blueman wrote:
>>>>>
>>>>>> Tuning USB suspend [1] in 4.3 on a Dell XPS 15 9553 (Skylake), I see a
>>>>>> kworker thread spinning in rpm_suspend [2].
>>>>>>
>>>>>> What is the most useful debug to get here beyond the immediate [3]?
>>>>>
>>>>> You can try doing:
>>>>>
>>>>>          echo 'module usbcore =p' >/sys/kernel/debug/dynamic_debug/control
>>>>
>>>> kworker and ksoftirqd spinning occurs when I echo 'auto' to all the
>>>> USB control entries. Using Alan's excellent tip, we see this being
>>>> logged repeatedly at a high rate:
>>>> [  353.245180] usb usb1-port4: status 0107 change 0000
>>>> [  353.245194] usb usb1-port12: status 0507 change 0000
>>>> [  353.245202] hub 1-0:1.0: state 7 ports 16 chg 0000 evt 0000
>>>> [  353.245203] hub 1-0:1.0: hub_suspend
>>>> [  353.245205] usb usb1: bus auto-suspend, wakeup 1
>>>> [  353.245206] usb usb1: bus suspend fail, err -16
>>>> [  353.245207] hub 1-0:1.0: hub_resume
>>>> ...
>>>>
>>>> So, EBUSY. Both the webcam is not open, and the bluetooth interface
>>>> [1] is rfkill'd; the situation occurs even if I unload all related
>>>> modules.
>>>>
>>>> What further debug would be useful?
>>>>
>>>> Thanks!
>>>>    Daniel
>>>>
>>>> -- [1]
>>>>
>>>> Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
>>>> Bus 001 Device 002: ID 0a5c:6410 Broadcom Corp.
>>>> Bus 001 Device 003: ID 1bcf:2b95 Sunplus Innovation Technology Inc.
>>>> Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
>>>
>>> Since bus 1 uses an xHCI controller, you should do:
>>>
>>>          echo 'module xhci-hcd =p' >/sys/kernel/debug/dynamic_debug/control
>>>
>>> I'm reasonably sure this will end up printing "suspend failed
>>> because a port is resuming", since that's the only place where
>>> xhci_bus_suspend() fails with -EBUSY, but you should try it to confirm
>>> this.
>>
>> I had to use:
>> echo 'module xhci_hcd =p' >/sys/kernel/debug/dynamic_debug/control
>>
>> and indeed we see:
>> [29172.246221] xhci_hcd 0000:00:14.0: get port status, actual port 11
>> status  = 0xe63
>> [29172.246222] xhci_hcd 0000:00:14.0: Get port status returned 0x507
>> [29172.246224] xhci_hcd 0000:00:14.0: get port status, actual port 12
>> status  = 0x2a0
>> [29172.246228] xhci_hcd 0000:00:14.0: get port status, actual port 13
>> status  = 0x2a0
>> [29172.246228] xhci_hcd 0000:00:14.0: Get port status returned 0x100
>> [29172.246231] xhci_hcd 0000:00:14.0: get port status, actual port 14
>> status  = 0x2a0
>> [29172.246232] xhci_hcd 0000:00:14.0: Get port status returned 0x100
>> [29172.246235] xhci_hcd 0000:00:14.0: Get port status returned 0x100
>> [29172.246248] xhci_hcd 0000:00:14.0: Get port status returned 0x100
>> [29172.246254] xhci_hcd 0000:00:14.0: Get port status returned 0x100
>> [29172.246264] xhci_hcd 0000:00:14.0: Get port status returned 0x100
>> [29172.246275] xhci_hcd 0000:00:14.0: Get port status returned 0x100
>> [29172.246285] xhci_hcd 0000:00:14.0: Get port status returned 0x507
>> [29172.246294] xhci_hcd 0000:00:14.0: get port status, actual port 14
>> status  = 0x2a0
>> [29172.246302] xhci_hcd 0000:00:14.0: suspend failed because a port is resuming
>> [29172.246321] xhci_hcd 0000:00:14.0: Get port status returned 0x107
>> [29172.246332] xhci_hcd 0000:00:14.0: get port status, actual port 6
>> status  = 0x2a0
>> [29172.246346] xhci_hcd 0000:00:14.0: Get port status returned 0x100
>> [29172.246359] xhci_hcd 0000:00:14.0: get port status, actual port 13
>> status  = 0x2a0
>> [29172.246364] xhci_hcd 0000:00:14.0: Get port status returned 0x100
>> [29172.246366] xhci_hcd 0000:00:14.0: get port status, actual port 15
>> status  = 0x2a0
>> [29172.246371] xhci_hcd 0000:00:14.0: suspend failed because a port is resuming
>> [29172.246380] xhci_hcd 0000:00:14.0: Get port status returned 0x100
>> [29172.246382] xhci_hcd 0000:00:14.0: get port status, actual port 1
>> status  = 0x2a0
>> [29172.246383] xhci_hcd 0000:00:14.0: Get port status returned 0x100
>
> It's time to get some assistance from the xhci-hcd maintainer.
>
> Mathias, Daniel's machine is spinning, trying to suspend the root hub
> on the xHCI HS/FS/LS bus and failing, over and over again.  It looks
> like either bus_state->resuming_ports or bus_state->port_remote_wakeup
> is nonzero when it shouldn't be.
>
> The information we have is all above.  Can you help Daniel debug this?
>
> Alan Stern
>

Looks like bits in bus_state->resuming_ports may be left uncleared.

We set a bit in bus_state->resuming_ports if we get a port status event with a port
in resume link state. We only clear it when a "get port status" request finds the port
in resume state with a resume timer passed 20ms.

If something happens during this 20ms to the port, and it moves to some other link state,
then resuming_ports is never cleared.

There is a fix for what now appears to be a subset of this issue in 4.4-rc2, clearing
the bus_state->resuming_ports in case host initiated resume code moved the port link to
U0 and before the "get port status" request finds the port in resume state.
I now see that this is not enough.

I'll write a patch reordering how we check flags, timers and link state in "get port status"

Daniel, can you test a patch like this if I write it for 4.3 kernel?

-Mathias
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