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

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Message-ID: <84a4f66a-5b0e-46a8-8746-be6cd7d49629@rowland.harvard.edu>
Date: Tue, 24 Sep 2024 09:38:13 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: duanchenghao <duanchenghao@...inos.cn>
Cc: Hongyu Xie <xy521521@...il.com>, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-usb@...r.kernel.org, niko.mauno@...sala.com, pavel@....cz,
	stanley_chang@...ltek.com, tj@...nel.org,
	Hongyu Xie <xiehongyu1@...inos.cn>
Subject: Re: [PATCH] USB: Fix the issue of task recovery failure caused by
 USB status when S4 wakes up

On Mon, Sep 23, 2024 at 04:00:35PM +0800, duanchenghao wrote:
> Hi Alan,
> 
> Do you think this plan is feasible, or is there any unclear part in my
> description that needs to be supplemented?

I apologize for not getting back to you earlier -- I've been incredibly 
busy during the last few weeks.

I still haven't had time to go over this throroughly.  If I don't 
respond by the end of this week, remind me again.

Alan Stern

> duanchenghao
> 
> 
> 在 2024-09-14星期六的 10:43 +0800，Hongyu Xie写道：
> > From: Hongyu Xie <xiehongyu1@...inos.cn>
> > 
> > 
> > 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@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
> > > 
> > 
> > Hongyu Xie
>