link state problem with dwc3 in supper-speed device mode

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Hi,

I run into a link state problem when dwc3 is in supper-speed device
mode.

Modprobe g_zero, link state is U3 (checked in DSTS).

After dwc3 is enumerated by the host, the trace on the bus is as:

[both Device and Host are in U0 now]
D->H: LGO_U1
H->D: LAU
D->H: LPMA

but actually dwc3 goes to U2. Is this expected?

Now remove the cable from the host, but dwc3 does not generate any
change, link state is still in U2, no any ftrace log either from the
point when removing the cable.

Now connect the cable again, dwc3 goes to SS.Inactive, shown in ftrace.
Of cause the host does not detect the attach at this point.

Then remove the cable, dwc3 changes as follows in ftrace:

RX.Detect
U0
U0
RX.Detect
U3

Basically the host does not enumerate dwc3 in every another attach.

Any comments about this problem? BTY, I checked with kernel v4.9-rc1,
v4.8, v4.4, v3.14 if it matters...

Thanks,
-Bin.
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