PRIME support scripts

On my W530 with Debian, Bumblebee didn't want to play with the nouveau driver, I did not want to install the proprietary nVidia drivers, the external connectors are powered by the discrete GPU and I did not want to have that enabled all the time for battery conservation.

This collection of scripts and configuration allows me to start the GPU when I need it, including the external connectors, but still have it disabled on boot saving battery.

Applications can be run on the discrete GPU using PRIME functionality.

Though it is pretty hacky, it should work alright with minor hickups.

What does what

I'll provide a short explanation of the purposes of the respective files

/etc/modules-load.d/prime.conf

• Force the bbswitch and i915 modules to be loaded at boot to provide power switching for the discrete GPU as well as a driver for the internal one.

/etc/modprobe.d/gpuoff.conf

• Prevents nouveau from getting loaded (limiting us to the intel card), so the discrete GPU does not power on
• Adds options to the bbswitch module to turn the card off on boot

/usr/local/sbin/load-nouveau

• Loads the nouveau module (blacklisted at boot), starting the discrete GPU

/etc/sudoers.d/gpu

• Allows users of the video group to run the /usr/local/sbin/load-nouveau as root. Making the script setuid would work, too, but this lets us limit execution to group members.

Setup

• Copy the configuration files to the appropriate locations
• Make sure bbswitch is installed and the module can be loaded
  • Test this by running modprobe bbswitch and/or modinfo bbswitch
  • Under Debian, installing bbswitch-dkms only provides you with the source, to actually build and use the module you need
    • the kernel-headers package for your current kernel installed
    • to run dpkg-reconfigure bbswitch-dkms to build and install the module
• Install the gpustart function and optionally the gpu alias (see below)
• Reboot your machine
• Check if the discrete card is off by looking at /proc/acpi/bbswitch
• Use the scripts as described below

Add start function to shell initialization

In my case, I add the following lines to ~/.zshrc:

alias gpu="DRI_PRIME=1"
gpustart(){
        sudo load-nouveau
        xrandr --setprovideroutputsource 1 0
        xrandr --setprovideroffloadsink 1 0
}

If xrandr --listproviders outputs useful names for you, you may replace the last two parameters to the xrandr calls with proper names. Otherwise you may need to figure out the correct order of the two cards with this guide.

Usage

• From within a running X server, run the gpustart function. On some intel drivers, this crashes the running X server, though with the KMS intel driver (which has other problems), this seemed to work seamlessly.
• If your X server dies, just start a new one and run the function again. You should now have access to the discrete card's outputs.
• To run applications on the discrete card, set the DRI_PRIME environment variable to 1 before running the target application. Alternatively, use the gpu alias.

Helpful

The current discrete card power status can be seen in /proc/acpi/bbswitch. Writing OFF to that file turns off the power to the card.

To see which card is being used to render, run glxinfo | grep -i opengl or glxgears -info.

Problems

Switching the card off again after usage is currently not implemented, but would involve stopping all PRIME clients, removing the sink assignments, switching off the card and unloading the nouveau driver kernel module in approximately that order.

The module load order in /etc/modules-load.d/prime.conf is important, as loading nouveau before the driver providing your display (eg i915), or indeed not loading it at all, will leave you with outputs named LVDS-2.

Ideas / Feedback / Future work

Some sources say that some (newer?) versions of nouveau provide internal power control, switching the card off when it is no longer required. This would allow me to stop using bbswitch for that purpose.