linux debugfs
Debugfs exists as a simple way for kernel developers to make information available to user space.
1. mount debugfs
1.1 no debugfs
1.2 mount
mount -t debugfs none /sys/kernel/debug
2. usb test
2.1 cat /sys/kernel/debug/usb/devices
we can know that host has two roothub and one mouse device.
2.2 dwc3 reg value
cat /sys/kernel/debug/300000.dwc3/regdump