linux-kernel - Re: Suspend to disk with usb connected fails to detect usb(reset) during resume

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Message-ID: <4ff09187-7ee7-78d0-82e2-bb3f763f181f@kernel.org>
Date:   Thu, 9 Nov 2017 09:17:05 -0600
From:   Dinh Nguyen <dinguyen@...nel.org>
To:     Ivid Suvarna <ivid.suvarna@...il.com>,
        Alan Stern <stern@...land.harvard.edu>
Cc:     USB list <linux-usb@...r.kernel.org>, balbi@...nel.org,
        gregkh@...uxfoundation.org, Billy Araujo <billyaraujo@...il.com>,
        johnyoun@...opsys.com, Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Kernel development list <linux-kernel@...r.kernel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Oliver Neukum <oneukum@...e.com>,
        Johan Hovold <johan@...nel.org>,
        Michal Nazarewicz <mina86@...a86.com>,
        Vincent Pelletier <plr.vincent@...il.com>,
        Jerry Zhang <zhangjerry@...gle.com>,
        John Keeping <john@...anate.com>,
        Krzysztof Opasiak <k.opasiak@...sung.com>,
        Abdulhadi Mohamed <abdulahhadi2@...il.com>,
        Matthew Wilcox <willy@...ux.intel.com>,
        Janusz Dziedzic <januszx.dziedzic@...ux.intel.com>
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 <stern@...land.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?
> 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.

Dinh