bad frequence with nvidia card (nouveau)

[lepetit]

hello, I have a laptop with a nvidia 330M graphics card (no igpu intel integrated)
since ubuntu 18.04, I noted that the frequencies used was not the lowest, which resulted in heating my laptop a little more.

an example, here are my frequencies of my graphics card:

cat /sys/kernel/debug/dri/0/pstate
03: core 135 MHz shader 270 MHz memory 135 MHz
07: core 405 MHz shader 810 MHz memory 324 MHz
0f: core 575 MHz shader 1265 MHz memory 790 MHz
DC: core 405 MHz shader 810 MHz memory 324 MHz

we can see here that the frequency 07: core 405 MHz shader 810 MHz 324 MHz memory are used
instead of frequencies 03: core 135 MHz shader 270 MHz memory 135 MHz

at each boot, I have to log in as root and modify it with the command:

echo 03 > /sys/kernel/debug/dri/0/pstate

is it a bug or is it wanted by ubuntu?

thank you

kernel : 4.15.0-29-generic

lsb_release -rd
Description: Ubuntu 18.04 LTS
Release: 18.04

apt-cache policy xserver-xorg-video-nouveau
xserver-xorg-video-nouveau:
  Installé : 1:1.0.15-2
  Candidat : 1:1.0.15-2
 Table de version :
 *** 1:1.0.15-2 500
        500 http://fr.archive.ubuntu.com/ubuntu bionic/main amd64 Packages
        100 /var/lib/dpkg/status