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1====================2USB port LED trigger3====================4 5This LED trigger can be used for signalling to the user a presence of USB device6in a given port. It simply turns on LED when device appears and turns it off7when it disappears.8 9It requires selecting USB ports that should be observed. All available ones are10listed as separated entries in a "ports" subdirectory. Selecting is handled by11echoing "1" to a chosen port.12 13Please note that this trigger allows selecting multiple USB ports for a single14LED.15 16This can be useful in two cases:17 181) Device with single USB LED and few physical ports19====================================================20 21In such a case LED will be turned on as long as there is at least one connected22USB device.23 242) Device with a physical port handled by few controllers25=========================================================26 27Some devices may have one controller per PHY standard. E.g. USB 3.0 physical28port may be handled by ohci-platform, ehci-platform and xhci-hcd. If there is29only 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 shown33below::34 35 echo usbport > trigger36 37This adds sysfs attributes to the LED that are documented in:38Documentation/ABI/testing/sysfs-class-led-trigger-usbport39 40Example use-case::41 42 echo usbport > trigger43 echo 1 > ports/usb1-port144 echo 1 > ports/usb2-port145 cat ports/usb1-port146 echo 0 > ports/usb1-port147