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

[Dinh Nguyen]

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