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

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Message-ID: <ac40c227-ea26-bccd-d254-5a2034103184@zhaoxin.com>
Date:   Wed, 16 Mar 2022 10:18:39 +0800
From:   "WeitaoWang-oc@...oxin.com" <WeitaoWang-oc@...oxin.com>
To:     Alan Stern <stern@...land.harvard.edu>
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 2022/3/15 11:18, Alan Stern wrote:
> 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?

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.


>> 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?
> 
It's 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,

This patch can fix pci driver's fail check in freeze_noirq phase.

Restoring system state from a hibernation image can continue and success.

Weitao Wang
>   	.thaw_noirq	= NULL,
>   	.thaw		= NULL,
>   	.poweroff	= hcd_pci_suspend,
> .
>