usb: chipidea: udc: disconnect/reconnect from host when do suspend/resume

In the Linux kernel, the following vulnerability has been resolved:

usb: chipidea: udc: disconnect/reconnect from host when do suspend/resume

Shawn and John reported a hang issue during system suspend as below:

- USB gadget is enabled as Ethernet - There is data transfer over USB Ethernet (scp a big file between host and device) - Device is going in/out suspend (echo mem > /sys/power/state)

The root cause is the USB device controller is suspended but the USB bus is still active which caused the USB host continues to transfer data with device and the device continues to queue USB requests (in this case, a delayed TCP ACK packet trigger the issue) after controller is suspended, however the USB controller clock is already gated off. Then if udc driver access registers after that point, the system will hang.

The correct way to avoid such issue is to disconnect device from host when the USB bus is not at suspend state. Then the host will receive disconnect event and stop data transfer in time. To continue make USB gadget device work after system resume, this will reconnect device automatically.

To make usb wakeup work if USB bus is already at suspend state, this will keep connection for it only when USB device controller has enabled wakeup capability.