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