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); 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. 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
