USB port LED trigger¶
This LED trigger can be used for signalling to the user a presence of USB devicein a given port. It simply turns on LED when device appears and turns it offwhen it disappears.
It requires selecting USB ports that should be observed. All available ones arelisted as separated entries in a “ports” subdirectory. Selecting is handled byechoing “1” to a chosen port.
Please note that this trigger allows selecting multiple USB ports for a singleLED.
This can be useful in two cases:
1) Device with single USB LED and few physical ports¶
In such a case LED will be turned on as long as there is at least one connectedUSB device.
2) Device with a physical port handled by few controllers¶
Some devices may have one controller per PHY standard. E.g. USB 3.0 physicalport may be handled by ohci-platform, ehci-platform and xhci-hcd. If there isonly one LED user will most likely want to assign ports from all 3 hubs.
This trigger can be activated from user space on led class devices as shownbelow:
echo usbport > trigger
This adds sysfs attributes to the LED that are documented in:Documentation/ABI/testing/sysfs-class-led-trigger-usbport
Example use-case:
echo usbport > triggerecho 1 > ports/usb1-port1echo 1 > ports/usb2-port1cat ports/usb1-port1echo 0 > ports/usb1-port1