On 26.2.2020 10.12, JC Kuo wrote: > Hi Thierry, > Yes, it can be verified with a LPM capable device. For example, a VIA USB 3.0 > hub is connected to Jetson-Xavier. "lsusb -v" output [1] shows the device > supports LPM and the host has enabled U1/U2 states for the device. If host LPM > is disabled, there will be no "U1 Enabled" and "U2 Enabled" strings in "Device > Status" section. > > To check LPM operation, disconnect all USB 3.0 devices from the hub and disable > runtime PM for the super-speed portion of the hub, so that it won't be > auto-suspended. > root@tegra-ubuntu:~# echo on > /sys/bus/usb/devices/2-4/power/control > > Since there is no data transaction for the hub, link will enter U2 soon. This > can be checked by reading XHCI.PORTSC register. In below, PLS (Port Link State) > field is U2. > root@tegra-ubuntu:~# devmem 0x3610450 > 0x00001243 A more human friendly way to read portsc registers: # cat /sys/kernel/debug/usb/xhci/0000\:00\:14.0/ports/port02/portsc Powered Connected Enabled Link:U0 PortSpeed:3 Change: Wake: -Mathias
