echo high > /sys/class/drm/card0/device/power_dpm_force_performance_level Permission denied?

I am trying to follow this tutorial:

• The first step is to run sudo su to switch to root. Done that.

• The second step is to run

  echo high > /sys/class/drm/card0/device/power_dpm_force_performance_level

• So I ran it, and here's what I got:

  bash: /sys/class/drm/card0/device/power_dpm_force_performance_level: Permission denied

Permission denied?! How is that and I am the root user? How is it possible?

I have no idea of the inputs you would need from me, so please tell me and I will reply to you asap.

EDIT

Here is the output ofecho high | sudo tee /sys/class/drm/card0/device/power_dpm_force_performance_leve‌​l (running as root):

tee: /sys/class/drm/card0/device/power_dpm_force_performance_leve‌​l: Permission denied
high

2 Answers

In: /sys/class/drm/cardX/device

$ cat power_dpm_force_performance_level
auto
$ echo manual > power_dpm_force_performance_level
$ cat power_dpm_force_performance_level
manual

$ cat power_dpm_state
balanced
$ echo performance > power_dpm_state
$ cat power_dpm_state
performance

OP probably already figured it out (hopefully), but for anyone else with this problem:

Check if the card is enabled/powered on.

On my laptop I got that error when my gpu wasn't being used. When I for example launched a game, it turned on and I could change the performance level.