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- USB port LED trigger
- ====================
- This LED trigger can be used for signalling to the user a presence of USB device
- in a given port. It simply turns on LED when device appears and turns it off
- when it disappears.
- It requires selecting USB ports that should be observed. All available ones are
- listed as separated entries in a "ports" subdirectory. Selecting is handled by
- echoing "1" to a chosen port.
- Please note that this trigger allows selecting multiple USB ports for a single
- LED. 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 connected
- USB 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 physical
- port may be handled by ohci-platform, ehci-platform and xhci-hcd. If there is
- only 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 shown
- below:
- 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 > trigger
- echo 1 > ports/usb1-port1
- echo 1 > ports/usb2-port1
- cat ports/usb1-port1
- echo 0 > ports/usb1-port1
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