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main/postmarketos-base: change permission on tm2-touchkey leds

Administrator requested to merge tm2-touchkey_leds_priviliges into master

This additional udev rule allows unpriviliged users to turn on/off the tm2-touchkey leds by echo 1 > /sys/class/leds/tm2-touchkey/brightness or echo 0 accordingly.

Until now, this needs to be done with sudo, e.g. echo 1 | sudo tee /sys/class/leds/tm2-touchkey/brightness or sudo /bin/sh -c 'echo 1 > /sys/class/leds/tm2-touchkey/brightness'.

The change is mainly beneficial for usage in userspace scripts . This way it's much easier to set up scripts for event-based handling of the leds.

Changing the permission the udev way by KERNEL=="tm2-touchkey", MODE="0666" did not work. Probably because of the same reason why turning them on/off by KERNEL=="tm2-touchkey", ATTR{brightness}="0" did not work. The latter causes a dmesg message saying udevd[...]: error opening ATTR{/sys/bus/i2c/drivers/tm2-touchkey/brightness} for writing: Permission denied. The reason for the message seems that the node /sys/bus/i2c/drivers/tm2-touchkey/brightness does not exist. I don't know why udev tries to handle it via /sys/bus/i2c.

Because of this, the permission on the tm2-touchkey leds are changed by a shell command within the udev rule.

Edited by Administrator

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