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

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Date:   Wed, 8 Nov 2017 17:59:19 +0530
From:   Ivid Suvarna <ivid.suvarna@...il.com>
To:     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, dinguyen@...nel.org,
        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 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.

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