1==================== 2USB port LED trigger 3==================== 4 5This LED trigger can be used for signalling to the user a presence of USB device 6in a given port. It simply turns on LED when device appears and turns it off 7when it disappears. 8 9It requires selecting USB ports that should be observed. All available ones are 10listed as separated entries in a "ports" subdirectory. Selecting is handled by 11echoing "1" to a chosen port. 12 13Please note that this trigger allows selecting multiple USB ports for a single 14LED. 15 16This can be useful in two cases: 17 181) Device with single USB LED and few physical ports 19==================================================== 20 21In such a case LED will be turned on as long as there is at least one connected 22USB device. 23 242) Device with a physical port handled by few controllers 25========================================================= 26 27Some devices may have one controller per PHY standard. E.g. USB 3.0 physical 28port may be handled by ohci-platform, ehci-platform and xhci-hcd. If there is 29only one LED user will most likely want to assign ports from all 3 hubs. 30 31 32This trigger can be activated from user space on led class devices as shown 33below:: 34 35 echo usbport > trigger 36 37This adds sysfs attributes to the LED that are documented in: 38Documentation/ABI/testing/sysfs-class-led-trigger-usbport 39 40Example use-case:: 41 42 echo usbport > trigger 43 echo 1 > ports/usb1-port1 44 echo 1 > ports/usb2-port1 45 cat ports/usb1-port1 46 echo 0 > ports/usb1-port1 47