USB LED Trigger in DTS; linux,default-trigger usage?

Hi all,

I created a pull request to get support for the Netgear EX6200v2 added and received some comments, I've worked through most of them but I'm getting tripped up on one comment suggesting to move the LED trigger for the USB port LED from 01_leds over to DTS.

This is what worked for triggering the LED when a device was connected under 01_leds

 ucidef_set_led_usbport "usb" "USB" "green:usb" "usb2-port1" "usb1-port1"

Note, this line in the pull request has additional terms for other triggers, since submitted the PR I've narrowed it down to what's above to be the minimum to get the LED to come on when a USB device is plugged in.

For moving this to DTS, I've added linux, default-trigger to the led node in my dts file and figured I could copy the triggers that worked in 01_leds but that doesn't seem to be the case.

Below I've gone into detail what I've found in the rabbit hole I went down but for starters, is there something about the usage that I'm ignoring for defining the trigger in DTS?

Looking at other commits, I see that most implementations have just 'usbport' as the trigger, however that hasn't worked for me, and neither worked when I first worked on getting the triggers to work in 01_leds.

I've also seen that some implementations list trigger-sources, typically calling labels ohci or echi ports; digging through the boot serial dump, it looks like there's an xhci hub

[    5.338506] xhci-hcd xHCI Host Controller
[    5.342991] xhci-hcd new USB bus registered, assigned bus nu
[    5.350881] xhci-hcd irq 164, io mem 0x08a00000
[    5.356798] usb usb1: New USB device found, idVendor=1d6b, idProduct=0002
[    5.363393] usb usb1: New USB device strings: Mfr=3, Product=2, SerialNumber=
[    5.370585] usb usb1: Product: xHCI Host Controller
[    5.375430] usb usb1: Manufacturer: Linux 3.14.43 xhci-hcd
[    5.380915] usb usb1: SerialNumber:
[    5.386418] hub 1-0:1.0: USB hub found
[    5.389566] hub 1-0:1.0: 1 port detected
[    5.393821] xhci-hcd xHCI Host Controller
[    5.398921] xhci-hcd new USB bus registered, assigned bus nu
[    5.406724] usb usb2: New USB device found, idVendor=1d6b, idProduct=0003
[    5.413304] usb usb2: New USB device strings: Mfr=3, Product=2, SerialNumber=
[    5.420498] usb usb2: Product: xHCI Host Controller
[    5.425344] usb usb2: Manufacturer: Linux 3.14.43 xhci-hcd
[    5.430827] usb usb2: SerialNumber:
[    5.436344] hub 2-0:1.0: USB hub found
[    5.439466] hub 2-0:1.0: 1 port detected
 usb_green {
                        label = "green:usb";
                        gpios = <&led_gpio 0 GPIO_ACTIVE_LOW>;
                        linux,default-trigger = "usb2-port1";
                        trigger-sources = <&xhci_hub>;