0001 ====================
0002 USB port LED trigger
0003 ====================
0004
0005 This LED trigger can be used for signalling to the user a presence of USB device
0006 in a given port. It simply turns on LED when device appears and turns it off
0007 when it disappears.
0008
0009 It requires selecting USB ports that should be observed. All available ones are
0010 listed as separated entries in a "ports" subdirectory. Selecting is handled by
0011 echoing "1" to a chosen port.
0012
0013 Please note that this trigger allows selecting multiple USB ports for a single
0014 LED.
0015
0016 This can be useful in two cases:
0017
0018 1) Device with single USB LED and few physical ports
0019 ====================================================
0020
0021 In such a case LED will be turned on as long as there is at least one connected
0022 USB device.
0023
0024 2) Device with a physical port handled by few controllers
0025 =========================================================
0026
0027 Some devices may have one controller per PHY standard. E.g. USB 3.0 physical
0028 port may be handled by ohci-platform, ehci-platform and xhci-hcd. If there is
0029 only one LED user will most likely want to assign ports from all 3 hubs.
0030
0031
0032 This trigger can be activated from user space on led class devices as shown
0033 below::
0034
0035 echo usbport > trigger
0036
0037 This adds sysfs attributes to the LED that are documented in:
0038 Documentation/ABI/testing/sysfs-class-led-trigger-usbport
0039
0040 Example use-case::
0041
0042 echo usbport > trigger
0043 echo 1 > ports/usb1-port1
0044 echo 1 > ports/usb2-port1
0045 cat ports/usb1-port1
0046 echo 0 > ports/usb1-port1
