linux-kernel - Re: `ohci_rh_resume()` called during `usb_dev

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Message-ID: <a8d7fe54-5fa8-3569-f615-5ee3d967fd18@molgen.mpg.de>
Date:   Tue, 24 Jul 2018 16:30:05 +0200
From:   Paul Menzel <pmenzel+linux-usb@...gen.mpg.de>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: `ohci_rh_resume()` called during `usb_dev_suspend()`

Dear Alan,


Thank you for your quick response.

On 07/24/18 16:21, Alan Stern wrote:
> On Tue, 24 Jul 2018, Paul Menzel wrote:

>> Profiling the suspend to and resume/wake-up from ACPI S3 with 
>> `sleepgraph.py` on an ASRock E350M1, I noticed that resume methods are 
>> called during suspend.
>>
>> Here is an excerpt from the callgraph.
>>
>>>   600.376906 |   0)   kworker-81   |               |  /* device_pm_callback_start: usb usb5, parent: 0000:00:14.5, type [suspend] */
>>>   600.376909 |   0)   kworker-81   |               |    usb_dev_suspend() {
>>>   600.376911 |   0)   kworker-81   |               |      usb_suspend() {
>>>   600.376913 |   0)   kworker-81   |               |        __pm_runtime_resume() {
>>>   600.376915 |   0)   kworker-81   |               |          _cond_resched() {
>>>   600.376917 |   0)   kworker-81   |   0.565 us    |            rcu_all_qs();
>>>   600.376921 |   0)   kworker-81   |   4.034 us    |          } /* _cond_resched */
>>>   600.376922 |   0)   kworker-81   |   0.505 us    |          _raw_spin_lock_irqsave();
>>>   600.376926 |   0)   kworker-81   |               |          rpm_resume() {
>>>   600.376928 |   0)   kworker-81   |   0.573 us    |            _raw_spin_lock();
>>>   600.376934 |   0)   kworker-81   |   0.706 us    |            rpm_resume();
>>>   600.376937 |   0)   kworker-81   |   0.556 us    |            _raw_spin_lock();
>>>   600.376942 |   0)   kworker-81   |   0.721 us    |            __rpm_get_callback();
>>>   600.376946 |   0)   kworker-81   |   0.564 us    |            dev_pm_disable_wake_irq_check();
>>>   600.376949 |   0)   kworker-81   |               |            rpm_callback() {
>>>   600.376952 |   0)   kworker-81   |               |              __rpm_callback() {
>>>   600.376954 |   0)   kworker-81   |               |                usb_runtime_resume() {
>>>   600.376956 |   0)   kworker-81   |               |                  usb_resume_both() {
>>>   600.376959 |   0)   kworker-81   |               |                    generic_resume() {
>>>   600.376960 |   0)   kworker-81   |               |                      hcd_bus_resume() {
>>>   600.376963 |   0)   kworker-81   |               |                        ohci_bus_resume [ohci_hcd]() {
>>>   600.376964 |   0)   kworker-81   |   0.588 us    |                          _raw_spin_lock_irq();
>>>   600.376968 |   0)   kworker-81   |               |                          ohci_rh_resume [ohci_hcd]() {
>>>   600.377043 |   0)   kworker-81   |               |                            msleep() {
>>
>> Please find the full callgraph and the HTML output attached.
>>
>> Is that expected?
> 
> I can't tell exactly what's happening from your callgraph and HTML, but
> yes, in general it is expected.
> 
> The reason is because some devices have different wakeup settings for
> runtime suspend and system suspend: A device that is enabled for wakeup
> signalling during runtime suspend often is not enabled for wakeup
> during system suspend.
> 
> As a result, the device's wakeup setting has to be changed when the 
> system goes to sleep, and to do that, we have to wake the device up 
> temporarily if it is already in runtime suspend.

Understood. Thank you for the explanation.

Sorry for being ignorant, but I have two more questions.

1.  Should this also happen, if no USB device is connected to a hub?

2.  If somebody point me to the code, how the callback(?)
    `pm_runtime_resume()` is hooked up in `usb_suspend()` that’d help
    me to better understand, what is going on.


Kind regards and thank you very much in advance,

Paul


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