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