42 lines
1.3 KiB
Plaintext
42 lines
1.3 KiB
Plaintext
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
|