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8dab9197 | 1 | ==================== |
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2 | USB port LED trigger |
3 | ==================== | |
4 | ||
5 | This LED trigger can be used for signalling to the user a presence of USB device | |
6 | in a given port. It simply turns on LED when device appears and turns it off | |
7 | when it disappears. | |
8 | ||
9 | It requires selecting USB ports that should be observed. All available ones are | |
10 | listed as separated entries in a "ports" subdirectory. Selecting is handled by | |
11 | echoing "1" to a chosen port. | |
12 | ||
13 | Please note that this trigger allows selecting multiple USB ports for a single | |
8dab9197 MCC |
14 | LED. |
15 | ||
16 | This can be useful in two cases: | |
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17 | |
18 | 1) Device with single USB LED and few physical ports | |
8dab9197 | 19 | ==================================================== |
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20 | |
21 | In such a case LED will be turned on as long as there is at least one connected | |
22 | USB device. | |
23 | ||
24 | 2) Device with a physical port handled by few controllers | |
8dab9197 | 25 | ========================================================= |
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26 | |
27 | Some devices may have one controller per PHY standard. E.g. USB 3.0 physical | |
28 | port may be handled by ohci-platform, ehci-platform and xhci-hcd. If there is | |
29 | only one LED user will most likely want to assign ports from all 3 hubs. | |
30 | ||
31 | ||
32 | This trigger can be activated from user space on led class devices as shown | |
8dab9197 | 33 | below:: |
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34 | |
35 | echo usbport > trigger | |
36 | ||
37 | This adds sysfs attributes to the LED that are documented in: | |
38 | Documentation/ABI/testing/sysfs-class-led-trigger-usbport | |
39 | ||
8dab9197 | 40 | Example use-case:: |
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41 | |
42 | echo usbport > trigger | |
43 | echo 1 > ports/usb1-port1 | |
44 | echo 1 > ports/usb2-port1 | |
45 | cat ports/usb1-port1 | |
46 | echo 0 > ports/usb1-port1 |