https://bugzilla.kernel.org/show_bug.cgi?id=60523
--- Comment #36 from Tobias Droste tdroste@gmx.de --- Hm I'm pretty sure the "stuck" power level is the same problem as the "write error: Invalid argument" problem.
Are you sure you're in the correct directory before executing the command?
If you're not in '/sys/class/drm/card0/device' you would just create a text file with 'high' or 'low' in it.