Permission group for system service

Hi!

I have created a kernel module (and insmod it at the start of the device) to control /dev/xx and only the system can access /dev/xx.
Thank to the code I have added, /dev/xx can be controlled from the Framework .
I now want to create a system service to handle this.

Which permission should be used for permissionGroup so that the service can access /dev/xx?

I have read the documentation (I am not able to post the link since I have less than 10 posts) but it doesn’t help me to guess the right permission group for the system service

PS: I am working on Marshmallow

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