ledtrig-usbport.rst 1.4 KB

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  1. ====================
  2. USB port LED trigger
  3. ====================
  4. This LED trigger can be used for signalling to the user a presence of USB device
  5. in a given port. It simply turns on LED when device appears and turns it off
  6. when it disappears.
  7. It requires selecting USB ports that should be observed. All available ones are
  8. listed as separated entries in a "ports" subdirectory. Selecting is handled by
  9. echoing "1" to a chosen port.
  10. Please note that this trigger allows selecting multiple USB ports for a single
  11. LED.
  12. This can be useful in two cases:
  13. 1) Device with single USB LED and few physical ports
  14. ====================================================
  15. In such a case LED will be turned on as long as there is at least one connected
  16. USB device.
  17. 2) Device with a physical port handled by few controllers
  18. =========================================================
  19. Some devices may have one controller per PHY standard. E.g. USB 3.0 physical
  20. port may be handled by ohci-platform, ehci-platform and xhci-hcd. If there is
  21. only one LED user will most likely want to assign ports from all 3 hubs.
  22. This trigger can be activated from user space on led class devices as shown
  23. below::
  24. echo usbport > trigger
  25. This adds sysfs attributes to the LED that are documented in:
  26. Documentation/ABI/testing/sysfs-class-led-trigger-usbport
  27. Example use-case::
  28. echo usbport > trigger
  29. echo 1 > ports/usb1-port1
  30. echo 1 > ports/usb2-port1
  31. cat ports/usb1-port1
  32. echo 0 > ports/usb1-port1