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Date:   Wed, 8 Nov 2017 10:42:25 -0500 (EST)
From:   Alan Stern <stern@rowland.harvard.edu>
To:     Ivid Suvarna <ivid.suvarna@gmail.com>
cc:     USB list <linux-usb@vger.kernel.org>, <balbi@kernel.org>,
        <gregkh@linuxfoundation.org>, Billy Araujo <billyaraujo@gmail.com>,
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        Janusz Dziedzic <januszx.dziedzic@linux.intel.com>
Subject: Re: Suspend to disk with usb connected fails to detect usb(reset)
 during resume
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On Wed, 8 Nov 2017, Ivid Suvarna wrote:

> On Tue, Nov 7, 2017 at 9:19 PM, Alan Stern <stern@rowland.harvard.edu> wrote:
> > On Tue, 7 Nov 2017, Ivid Suvarna wrote:
> >
> >> Hi,
> >>
> >> I am trying to support suspend to disk(hibernate) on Hikey with 4.4
> >> kernel. During suspend, I could see the usb devices getting reset and I
> >> can access them properly. Message can be seen as below:
> >>
> >> usb 1-1: reset high-speed USB device number 2 using dwc2
> >> usb 1-1.2: reset high-speed USB device number 3 using dwc2
> >> usb 1-1.2.4: reset high-speed USB device number 4 using dwc2
> >
> > You might start by asking why the devices need to be reset during
> > suspend.  I can't see any reason for doing this.
> >
> > Alan Stern
> >
> 
> Yes please. Could you explain as to why the usb needs to reset while
> suspending?

I cannot explain it.  USB devices do not need to be reset during system 
suspend.

Alan Stern

> This scenario is also observed in normal suspend to ram.
> 
> And why the USB gets disconnected on resume from hibernation.
> I checked the register dump of usb in /sys/kernel/debug and all
> registers after resume have zero value.
> 
> But if I run "usb start" from uboot and then resume, I see that usb
> gets initialized again and I am able to use USB on resume.
> 
> Thanks,
> Ivid


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