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Diffstat (limited to 'Documentation/leds/ledtrig-usbport.rst')
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diff --git a/Documentation/leds/ledtrig-usbport.rst b/Documentation/leds/ledtrig-usbport.rst new file mode 100644 index 000000000..37c2505bf --- /dev/null +++ b/Documentation/leds/ledtrig-usbport.rst @@ -0,0 +1,46 @@ +==================== +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 |