[PATCH v2] usb: dwc2: add bus suspend/resume for dwc2

[Julius Werner]

>> The contract for bus_suspend() is that it will suspend all ports not
>> yet suspended, keep track of those ports and then only resume those in
>> bus_resume() (compare, for example, how XHCI keeps track of that with
>> xhci_bus_state.bus_suspended in xhci_bus_suspend/resume()). So you
>> need something here to remember whether this function suspended the
>> port or whether it had already been suspended, and then only resume
>> the port in bus_resume() in the former case.
>
> In fact, the dwc2 controller only support one port, so the hprt0
> is the only one port we need to care.

Yes, I know, but that one port still needs to play by the rules the
USB core expects. All I'm saying is: if the port was already suspended
during bus_suspend(), then the next bus_resume() should not resume it.

The rest looks good to me now. But in order to get it really working,
I think we'll still need the actual driver.pm suspend/resume methods,
at least for the HCD_FLAG_HW_ACCESSIBLE and the
usb_root_hub_lost_power() handling (probably better in a separate
patch).