1*4882a593Smuzhiyun==================== 2*4882a593SmuzhiyunUSB port LED trigger 3*4882a593Smuzhiyun==================== 4*4882a593Smuzhiyun 5*4882a593SmuzhiyunThis LED trigger can be used for signalling to the user a presence of USB device 6*4882a593Smuzhiyunin a given port. It simply turns on LED when device appears and turns it off 7*4882a593Smuzhiyunwhen it disappears. 8*4882a593Smuzhiyun 9*4882a593SmuzhiyunIt requires selecting USB ports that should be observed. All available ones are 10*4882a593Smuzhiyunlisted as separated entries in a "ports" subdirectory. Selecting is handled by 11*4882a593Smuzhiyunechoing "1" to a chosen port. 12*4882a593Smuzhiyun 13*4882a593SmuzhiyunPlease note that this trigger allows selecting multiple USB ports for a single 14*4882a593SmuzhiyunLED. 15*4882a593Smuzhiyun 16*4882a593SmuzhiyunThis can be useful in two cases: 17*4882a593Smuzhiyun 18*4882a593Smuzhiyun1) Device with single USB LED and few physical ports 19*4882a593Smuzhiyun==================================================== 20*4882a593Smuzhiyun 21*4882a593SmuzhiyunIn such a case LED will be turned on as long as there is at least one connected 22*4882a593SmuzhiyunUSB device. 23*4882a593Smuzhiyun 24*4882a593Smuzhiyun2) Device with a physical port handled by few controllers 25*4882a593Smuzhiyun========================================================= 26*4882a593Smuzhiyun 27*4882a593SmuzhiyunSome devices may have one controller per PHY standard. E.g. USB 3.0 physical 28*4882a593Smuzhiyunport may be handled by ohci-platform, ehci-platform and xhci-hcd. If there is 29*4882a593Smuzhiyunonly one LED user will most likely want to assign ports from all 3 hubs. 30*4882a593Smuzhiyun 31*4882a593Smuzhiyun 32*4882a593SmuzhiyunThis trigger can be activated from user space on led class devices as shown 33*4882a593Smuzhiyunbelow:: 34*4882a593Smuzhiyun 35*4882a593Smuzhiyun echo usbport > trigger 36*4882a593Smuzhiyun 37*4882a593SmuzhiyunThis adds sysfs attributes to the LED that are documented in: 38*4882a593SmuzhiyunDocumentation/ABI/testing/sysfs-class-led-trigger-usbport 39*4882a593Smuzhiyun 40*4882a593SmuzhiyunExample use-case:: 41*4882a593Smuzhiyun 42*4882a593Smuzhiyun echo usbport > trigger 43*4882a593Smuzhiyun echo 1 > ports/usb1-port1 44*4882a593Smuzhiyun echo 1 > ports/usb2-port1 45*4882a593Smuzhiyun cat ports/usb1-port1 46*4882a593Smuzhiyun echo 0 > ports/usb1-port1 47