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Date:   Thu, 9 Nov 2017 09:17:05 -0600
From:   Dinh Nguyen <>
To:     Ivid Suvarna <>,
        Alan Stern <>
Cc:     USB list <>,,, Billy Araujo <>,, Felipe Balbi <>,
        Kernel development list <>,
        Laurent Pinchart <>,
        Oliver Neukum <>,
        Johan Hovold <>,
        Michal Nazarewicz <>,
        Vincent Pelletier <>,
        Jerry Zhang <>,
        John Keeping <>,
        Krzysztof Opasiak <>,
        Abdulhadi Mohamed <>,
        Matthew Wilcox <>,
        Janusz Dziedzic <>
Subject: Re: Suspend to disk with usb connected fails to detect usb(reset)
 during resume

On 11/08/2017 06:29 AM, Ivid Suvarna wrote:
> On Tue, Nov 7, 2017 at 9:19 PM, Alan Stern <> 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?
> 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.

Registers with zero value is indicative of a clock not getting turned
on, at least that I have encountered with DWC2 on the SoCFPGA platform.


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