root user cannot write on file

Hi,

I was trying to edit the following file as root:

/sys/module/pcie_aspm/parameters/policy

As in the title I cannot write on this file even though I am logged as root.

Permissions on this file are set rwx for owner, group, and others (chmod 777)

I tried to overwrite the file by using 'echo "string" >/sys/module/pcie_aspm/parameters/policy' and through vi/vim/nano

I also trying to set chattr attribute by typing:
chattr -a /sys/module/pcie_aspm/parameters/policy
chattr -i /sys/module/pcie_aspm/parameters/policy

both returning: "inappropriate ioctl for device"

Do you know how I can write the file?

Thanks for you time