47 lines
1.4 KiB
ReStructuredText
47 lines
1.4 KiB
ReStructuredText
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====================
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USB port LED trigger
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====================
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This LED trigger can be used for signalling to the user a presence of USB device
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in a given port. It simply turns on LED when device appears and turns it off
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when it disappears.
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It requires selecting USB ports that should be observed. All available ones are
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listed as separated entries in a "ports" subdirectory. Selecting is handled by
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echoing "1" to a chosen port.
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Please note that this trigger allows selecting multiple USB ports for a single
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LED.
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This can be useful in two cases:
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1) Device with single USB LED and few physical ports
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====================================================
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In such a case LED will be turned on as long as there is at least one connected
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USB device.
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2) Device with a physical port handled by few controllers
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=========================================================
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Some devices may have one controller per PHY standard. E.g. USB 3.0 physical
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port may be handled by ohci-platform, ehci-platform and xhci-hcd. If there is
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only one LED user will most likely want to assign ports from all 3 hubs.
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This trigger can be activated from user space on led class devices as shown
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below::
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echo usbport > trigger
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This adds sysfs attributes to the LED that are documented in:
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Documentation/ABI/testing/sysfs-class-led-trigger-usbport
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Example use-case::
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echo usbport > trigger
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echo 1 > ports/usb1-port1
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echo 1 > ports/usb2-port1
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cat ports/usb1-port1
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echo 0 > ports/usb1-port1
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