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

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Message-ID: <YjCuOXRFZ8CjK9SD@rowland.harvard.edu>
Date:   Tue, 15 Mar 2022 11:18:17 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     "WeitaoWang-oc@...oxin.com" <WeitaoWang-oc@...oxin.com>
Cc:     gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, CobeChen@...oxin.com,
        TimGuo@...oxin.com, tonywwang@...oxin.com, weitaowang@...oxin.com
Subject: Re: [PATCH] USB:Fix ehci infinite suspend-resume loop issue in
 zhaoxin

On Tue, Mar 15, 2022 at 08:39:09PM +0800, WeitaoWang-oc@...oxin.com wrote:
> On 2022/3/14 10:24, Alan Stern wrote:
> > > +       t1 = ehci_readl(ehci, &ehci->regs->status);
> > > +       ehci_writel(ehci, t1 & STS_PCD, &ehci->regs->status);
> > > +       ehci_readl(ehci, &ehci->regs->status);
> > 
> > You should not clear the STS_PCD bit.  What if some other port had a
> > status change at the same time?  Then because you cleared the
> > port-change-detect bit, the system would not realize that the other port
> > needed to be handled.
> 
> I really didn't think about this case.
> 
> > Leaving the STS_PCD bit turned on will cause the driver to do a little
> > extra work, but it shouldn't cause any harm.
> > 
> I have encountered the following situation if EHCI runtime suspend is
> enabled by default.
> 
> 
> 
> 1.Wake from system to disk and boot OS.

You're talking about resuming after hibernation, 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?

> 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.

> 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?

You know, I'm not at all certain that the callbacks for freeze and 
freeze_noirq should ever return anything other than 0.  It's okay for 
them to call check_root_hub_suspended(), but they should ignore its 
return value.

Can you check if the patch below helps?

Alan Stern


Index: usb-devel/drivers/usb/core/hcd-pci.c
===================================================================
--- usb-devel.orig/drivers/usb/core/hcd-pci.c
+++ usb-devel/drivers/usb/core/hcd-pci.c
@@ -575,6 +575,12 @@ static int hcd_pci_resume(struct device
 	return resume_common(dev, PM_EVENT_RESUME);
 }
 
+static int hcd_pci_freeze_check(struct device *dev)
+{
+	(void) check_root_hub_suspended(dev);
+	return 0;
+}
+
 static int hcd_pci_restore(struct device *dev)
 {
 	return resume_common(dev, PM_EVENT_RESTORE);
@@ -586,6 +592,7 @@ static int hcd_pci_restore(struct device
 #define hcd_pci_suspend_noirq	NULL
 #define hcd_pci_resume_noirq	NULL
 #define hcd_pci_resume		NULL
+#define hcd_pci_freeze_check	NULL
 #define hcd_pci_restore		NULL
 
 #endif	/* CONFIG_PM_SLEEP */
@@ -616,8 +623,8 @@ const struct dev_pm_ops usb_hcd_pci_pm_o
 	.suspend_noirq	= hcd_pci_suspend_noirq,
 	.resume_noirq	= hcd_pci_resume_noirq,
 	.resume		= hcd_pci_resume,
-	.freeze		= check_root_hub_suspended,
-	.freeze_noirq	= check_root_hub_suspended,
+	.freeze		= hcd_pci_freeze_check,
+	.freeze_noirq	= hcd_pci_freeze_check,
 	.thaw_noirq	= NULL,
 	.thaw		= NULL,
 	.poweroff	= hcd_pci_suspend,