Commit | Line | Data |
---|---|---|
0f247626 RM |
1 | USB port LED trigger |
2 | ==================== | |
3 | ||
4 | This LED trigger can be used for signalling to the user a presence of USB device | |
5 | in a given port. It simply turns on LED when device appears and turns it off | |
6 | when it disappears. | |
7 | ||
8 | It requires selecting USB ports that should be observed. All available ones are | |
9 | listed as separated entries in a "ports" subdirectory. Selecting is handled by | |
10 | echoing "1" to a chosen port. | |
11 | ||
12 | Please note that this trigger allows selecting multiple USB ports for a single | |
13 | LED. This can be useful in two cases: | |
14 | ||
15 | 1) Device with single USB LED and few physical ports | |
16 | ||
17 | In such a case LED will be turned on as long as there is at least one connected | |
18 | USB device. | |
19 | ||
20 | 2) Device with a physical port handled by few controllers | |
21 | ||
22 | Some devices may have one controller per PHY standard. E.g. USB 3.0 physical | |
23 | port may be handled by ohci-platform, ehci-platform and xhci-hcd. If there is | |
24 | only one LED user will most likely want to assign ports from all 3 hubs. | |
25 | ||
26 | ||
27 | This trigger can be activated from user space on led class devices as shown | |
28 | below: | |
29 | ||
30 | echo usbport > trigger | |
31 | ||
32 | This adds sysfs attributes to the LED that are documented in: | |
33 | Documentation/ABI/testing/sysfs-class-led-trigger-usbport | |
34 | ||
35 | Example use-case: | |
36 | ||
37 | echo usbport > trigger | |
38 | echo 1 > ports/usb1-port1 | |
39 | echo 1 > ports/usb2-port1 | |
40 | cat ports/usb1-port1 | |
41 | echo 0 > ports/usb1-port1 |