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linux/Documentation/ABI/testing/sysfs-class-led-trigger-usbport

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usb: core: Introduce a USB port LED trigger This commit adds a new trigger responsible for turning on LED when USB device gets connected to the selected USB port. This can can useful for various home routers that have USB port(s) and a proper LED telling user a device is connected. The trigger gets its documentation file but basically it just requires enabling it and selecting USB ports (e.g. echo 1 > ports/usb1-1). There was a long discussion on design of this driver. Its current state is a result of picking them most adjustable solution as others couldn't handle all cases. 1) It wasn't possible for the driver to register separated trigger for each USB port. Some physical USB ports are handled by more than one controller and so by more than one USB port. E.g. USB 2.0 physical port may be handled by OHCI's port and EHCI's port. It's also not possible to assign more than 1 trigger to a single LED and implementing such feature would be tricky due to syncing triggers and sysfs conflicts with old triggers. 2) Another idea was to register trigger per USB hub. This wouldn't allow handling devices with multiple USB LEDs and controllers (hubs) controlling more than 1 physical port. It's common for hubs to have few ports and each may have its own LED. This final trigger is highly flexible. It allows selecting any USB ports for any LED. It was also modified (comparing to the initial version) to allow choosing ports rather than having user /guess/ proper names. It was successfully tested on SmartRG SR400ac which has 3 USB LEDs, 2 physical ports and 3 controllers. It was noted USB subsystem already has usb-gadget and usb-host triggers but they are pretty trivial ones. They indicate activity only and can't have ports specified. In future it may be good idea to consider adding activity support to usbport as well. This should allow switching to this more generic driver and maybe marking old ones as obsolete. This can be implemented with another sysfs file for setting mode. The default mode wouldn't change so there won't be ABI breakage and so such feature can be safely implemented later. There was also an idea of supporting other devices (PCI, SDIO, etc.) but as this driver already contains some USB specific code (and will get more) these should be probably separated drivers (triggers). Signed-off-by: Rafał Miłecki <rafal@milecki.pl> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2016-09-16 22:13:48 +08:00
What: /sys/class/leds/<led>/ports/<port>
Date: September 2016
KernelVersion: 4.9
Contact: linux-leds@vger.kernel.org
linux-usb@vger.kernel.org
Description:
Every dir entry represents a single USB port that can be
selected for the USB port trigger. Selecting ports makes trigger
observing them for any connected devices and lighting on LED if
there are any.
Echoing "1" value selects USB port. Echoing "0" unselects it.
Current state can be also read.
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