Re: [PATCH] USB:Fix ehci infinite suspend-resume loop issue in zhaoxin

[WeitaoWang-oc@xxxxxxxxxxx]

On 2022/4/6 00:02, Alan Stern wrote:
> On Wed, Mar 16, 2022 at 10:18:39AM +0800, WeitaoWang-oc@xxxxxxxxxxx wrote:
> > On 2022/3/15 11:18, Alan Stern wrote:
> > > On Tue, Mar 15, 2022 at 08:39:09PM +0800, WeitaoWang-oc@xxxxxxxxxxx wrote:
> > > > I have encountered the following situation if EHCI runtime suspend is
> > > > enabled by default.
>
> Some things about this still confuse me...
>
> > > > 1.Wake from system to disk and boot OS.
> > >
> > > You're talking about resuming after hibernation, right?
> >
> > You're right.
> > > > 2.EHCI will entry runtime suspend after enumerated by driver during boot
> > > > phase of suspend to disk
> > >
> > > I'm not sure what you mean by "boot phase of suspend to disk".  This is
> > > while the restore kernel is starting up at the beginning of resume from
> > > hibernation, right?
> > You understood exactly what I was saying.
>
> Okay, so we're waking up from hibernation.
>
> > > > 3.EHCI will be placed to freeze state and ehci_resume is called after image
> > > > is loaded.
> > >
> > > ehci_resume is called to leave runtime suspend.  Going into the freeze
> > > state doesn't require any changes.
>
> In fact, the resume kernel doesn't call ehci_resume at all.  Here's what
> it does:
>
> 	The resume kernel boots;
>
> 	If your patch causes STS_PCD to be set at this point, the flag
> 	should get cleared shortly afterward by ehci_irq;
>
> 	ehci-hcd goes into runtime suspend;
>
> 	The kernel reads the system image that was stored earlier when
> 	hibernation began;
>
> 	After the image is loaded, the system goes into the freeze
> 	state (this does not call any routines in ehci-hcd);
On this phase, pci_pm_freeze will be called for pci device. In this
function, pm_runtime_resume will be called to resume already
runtime-suspend devices. which will cause ehci_resume to be called.
Thus STS_PCD flag will be set in ehci_resume function.

Thanks
Weitao Wang
> 	The resume kernel transfers control to the image kernel;
>
> Now the image kernel is running.  It goes into the restore state, which
> involves calling ehci_resume.  Presumably your patch cases the STS_PCD
> flag to get set at this point.
> o
> But that's all!  The system is now back up, out of hibernation, and
> running normally.  There are no more calls to check_root_hub_suspended
>
> > > > 4.If PCD flag is set(caused by patch), then HCD_FLAG_RH_RUNNING will be set.
> > > >
> > > > 5.Pci_pm_freeze_noirq is called to check ehci root hub state and return
> > > > value is -EBUSY. which will cause
> > > >    quiesce phase of suspend to disk fail.
> > >
> > > You're talking about check_root_hub_suspended() in hcd-pci.c, right?
> > It's right.
>
> So how can this happen, given that the image kernel doesn't call
> pci_pm_freeze_noirq?
>
> Alan Stern
> .