Messages in this thread | | | Date | Wed, 6 Apr 2022 10:38:28 +0800 | Subject | Re: [PATCH] USB:Fix ehci infinite suspend-resume loop issue in zhaoxin | From | "" <> |
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On 2022/4/6 00:02, Alan Stern wrote: > On Wed, Mar 16, 2022 at 10:18:39AM +0800, WeitaoWang-oc@zhaoxin.com wrote: >> On 2022/3/15 11:18, Alan Stern wrote: >>> On Tue, Mar 15, 2022 at 08:39:09PM +0800, WeitaoWang-oc@zhaoxin.com 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 > .
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