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

Alan Stern
2024-09-12T15:00:32Z

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.

> > Is your problem related to the one discussed in this email thread?
> >
> > https://lore.kernel.org/linux-usb/d8600868-6e4b-45ab-b328-852b6ac8ecb5@rowland.harvard.edu/
> >
> > 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