| 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 |
