Using the module on SteamOS is possible but some additional steps are required because Valve has made the root filesystem read-only by default.
First, switch to desktop mode and run these commands in the terminal to set up the package manager:
sudo steamos-readonly disable
sudo pacman-key --init
sudo pacman-key --populate archlinux holo
Install the base development tools and kernel headers (accept all packages when prompted):
sudo pacman -S --needed base-devel "$(cat /usr/lib/modules/$(uname -r)/pkgbase)-headers"
These commands will download and build the module. They only need to be executed once.
git clone https://github.com/hannesmann/gcadapter-oc-kmod.git
cd gcadapter-oc-kmod
make
# optional step, to relock the filesystem
sudo steamos-readonly enable
The last command needs to be executed every time you restart the device (but it persists when switching in and out of desktop mode):
sudo insmod gcadapter_oc.ko
These steps need to be repeated every time you update SteamOS. If Valve updates their kernel, the old module you built will no longer work (insmod will tell you when there's a problem).