Re: [PATCH] USB: Fix the issue of task recovery failure caused by USB status when S4 wakes up

[Hongyu Xie]

From: Hongyu Xie <xiehongyu1@xxxxxxxxxx>


Hi Alan,
On 2024/9/12 23:00, Alan Stern wrote:
> On Thu, Sep 12, 2024 at 11:21:26AM +0800, duanchenghao wrote:
> > 在 2024-09-11星期三的 10:40 -0400，Alan Stern写道：
> > > On Tue, Sep 10, 2024 at 05:36:56PM +0800, duanchenghao wrote:
> > > > S4 wakeup restores the image that was saved before the system
> > > > entered
> > > > the S4 sleep state.
> > > >
> > > >      S4 waking up from hibernation
> > > >      =============================
> > > >      kernel initialization
> > > >      |
> > > >      v
> > > >      freeze user task and kernel thread
> > > >      |
> > > >      v
> > > >      load saved image
> > > >      |
> > > >      v
> > > >      freeze the peripheral device and controller
> > > >      (Check the HCD_FLAG_WAKEUP_ PENDING flag of the USB. If it is
> > > > set,
> > > >       return to EBUSY and do not perform the following restore
> > > > image.)
> > >
> > > Why is the flag set at this point?  It should not be; the device and
> > > controller should have been frozen with wakeup disabled.
> > This is check point, not set point.
>
> Yes, I know that.  But when the flag was checked, why did the code find
> that it was set?  The flag should have been clear.
Maybe duanchenghao means this,
freeze_kernel_threads
load_image_and_restore
  suspend roothub
                                     interrupt occurred
                                       usb_hcd_resume_root_hub
                                         set HCD_FLAG_WAKEUP_PENDING
                                         queue_work // freezed
  suspend pci
    return -EBUSY  because HCD_FLAG_WAKEUP_PENDING

So s4 resume failed.
> > > Is your problem related to the one discussed in this email thread?
> > >
> > > https://lore.kernel.org/linux-usb/d8600868-6e4b-45ab-b328-852b6ac8ecb5@xxxxxxxxxxxxxxxxxxx/
> > >
> > > Would the suggestion I made there -- i.e., have the xhci-hcd
> > > interrupt handler skip calling usb_hcd_resume_root_hub() if the root
> > > hub
> > > was suspended with wakeup = 0 -- fix your problem?
> >
> > Skipping usb_hcd_resume_root_hub() should generally be possible, but
> > it's important to ensure that normal remote wakeup functionality is not
> > compromised. Is it HUB_SUSPEND that the hub you are referring to is in
> > a suspended state?
>
> I don't understand this question.  hub_quiesce() gets called with
> HUB_SUSPEND when the hub enters a suspended state.
>
> You are correct about the need for normal remote wakeup to work
> properly.  The interrupt handler should skip calling
> usb_hcd_resume_root_hub() for port connect or disconnect changes and for
> port overcurrent changes (when the root hub is suspended with wakeup =
> 0).  But it should _not_ skip calling usb_hcd_resume_root_hub() for port
> resume events.
>
> Alan Stern

Hongyu Xie