Finding power switch GPIO/ testing all possible GPIO

Ok it works so the important thing is to add "ephy" to "ralink,group =", this releases ephy gpio including gpio 42.

I will use wt3020h.dts profile for now: it works well for this board.

Thanks to everyone for ther help!

To enable 3g power you need to do:

echo "42" > /sys/class/gpio/export
echo "out" > /sys/class/gpio/gpio42/direction
echo "1" > /sys/class/gpio/gpio42/value

@juppin A bit off topic,but not so much.
Do you know a way to check which GPIOs are exported in non DTS system?

If you're lucky you can mount -t debugfs none /sys/kernel/debug and then you can explore /sys/kernel/debug/pinctrl/ and /sys/kernel/debug/gpio.

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No luck.
mount: mounting none on /sys/kernel/debug failed: No such file or directory