GPU switching for 2010 Macbook Pros

This is highly experimental. Expect crashes and lockups. Even though I haven't experienced anything serious, I'm not responsible if it causes your Macbook to explode or worse.

Prerequisites:
    A running Ubuntu 12.04 system, booting via Bootcamp/BIOS
    envytools: https://github.com/pathscale/envytools
    optional: NVIDIA proprietary driver 
        (install nvidia-current, but keep it blacklisted in /etc/modprobe.d, make sure nouveau is _not_ blacklisted)
    optional: Bumblebee: https://wiki.ubuntu.com/Bumblebee
    really useful: Setup ssh and networking so it's automatically available after boot. 
        Checking "Available to all users" in the configuration dialog should do the trick.

    It's also useful to have a dump of your vbios and to know what PDISPLAY_VGA_ROM_WINDOW should be. Run get_vbios.sh and get_rom_window.sh. The output of get_rom_window.sh should be something like "00619f04: 000ffe09".
    Make sure there is _no_ /etc/X11/xorg.conf, xorg should start on the right card automatically.

Installation:
1. Compile and install the patched kernel
    $ git clone git@github.com:ah-/ubuntu-kernel-mbp.git
    $ cd ubuntu-kernel-mbp
    $ git checkout gmux
    $ fakeroot debian/rules clean
    $ skipabi=true skipmodule=true fakeroot debian/rules binary-indep
    $ skipabi=true skipmodule=true fakeroot debian/rules binary-perarch
    $ skipabi=true skipmodule=true fakeroot debian/rules binary-mbp
    $ cd ..
    $ sudo dpkg -i *deb
    (see also http://blog.avirtualhome.com/2012/01/13/compile-linux-kernel-3-2-for-ubuntu-11-10/, section Compile)
2. Boot into the new kernel
3. Compile and install the apple_gmux switching driver
    $ https://github.com/ah-/gmux
    $ cd gmux
    $ make
    $ sudo cp apple_gmux.ko /lib/modules/3.2.0-18-mbp/kernel/drivers/platform/x86/apple-gmux.ko
4. Configure Grub
    see gmux-scripts/conf menuentries
    If you want output during boot don't forget 
        set gfxpayload=console (for BIOS)
    or
        set gfxpayload=keep
        insmod (hd1,gpt1)/efi/grub/efi_gop.mod
        terminal_output gfxterm
    for EFI.
    You also need a few boot parameters:
        i915.lvds_channel=2
            See http://lists.freedesktop.org/archives/intel-gfx/2012-March/015499.html
        i915.modeset=1 i915.lvds_use_ssc=0
        i5s_enable_igd=1
            Quirk to enable the Intel Integrated Graphics in BIOS mode
        i5s_3400s_force_ahci=1
            Quirk to enable AHCI in BIOS mode (not necessary, but useful)
        drm.debug=0x14 log_buf_len=16M
            To get a lot of debug output in case anything goes wrong
        text
            Boot into text console, not X, just to be safe
5. Configure bumblebee:
    Make sure it isn't started automatically on boot
    Copy the configuration from gmux-scripts/conf/bumblebee to /etc/bumblebee

Usage:
    Get the current status:
        $ cat /sys/kernel/debug/vgaswitcheroo/switch
    After boot the NVIDIA card is active. Switch between both cards with
        $ echo IGD > /sys/kernel/debug/vgaswitcheroo/switch
        $ echo DIS > /sys/kernel/debug/vgaswitcheroo/switch
    You can also tell it to do a delayed switch (wait until X is stopped, then switch)
        $ echo DIGD > /sys/kernel/debug/vgaswitcheroo/switch
        $ echo DDIS > /sys/kernel/debug/vgaswitcheroo/switch
    And power the card not in use on/off:
        $ echo ON > /sys/kernel/debug/vgaswitcheroo/switch
        $ echo OFF > /sys/kernel/debug/vgaswitcheroo/switch
    Start/stop X:
        $ start lightm
        $ stop lightm
    Use the dedicated card on demand with bumblebee (with nouveau):
        # switch to IGD, start lightdm, log in before
        $ cd gmux-scripts/bin
        $ ./bumblebee-nouveau.sh
        # in another terminal
        $ optirun glxspheres
        $ optirun bash
        # stop ./bumblebee-nouveau.sh with ctrl-c
    Use the dedicated card on demand with bumblebee (with nvidia blob):
        See above, replace nouveau with nvidia
        Don't forget to dump the vbios before and check PDISPLAY_VGA_ROM_WINDOW
    Start X with nvidia blob:
        # switch to dedicated card, using nouveau
        $ echo DIS > /sys/kernel/debug/vgaswitcheroo/switch
        $ cd gmux-scripts/bin
        $ ./nvidia_load.sh
    Stop X after using it with the nvidia blob:
        # use nohup so the script keeps running even after lightdm is stopped
        $ nohup ./nvidia_unload.sh &
        $ stop lightdm
        # then switch to a text console with ctrl-alt-f1

Known issues:
    No output when booting:
        Boot with set gfxpayload=console for text during boot
    There's no text console when using the nvidia X driver:
        That isn't specific to graphics switching, go bug Nvidia
    Instabilities when unloading drivers/suspending while the dedicated card is powered off:
        Suspend doesn't work reliably yet
        Power the dedicated card on using echo ON > /sys/kernel/debug/vgaswitcheroo/switch before doing anything with it
    OpenGL doesn't work:
        Check update-alternatives --config x86_64-linux-gnu_gl_conf, select mesa for i915/nouveau and nvidia for the nvidia blob
    nvidia blob: NVRM: RmInitAdapter failed! (0x30:0xffffffff:858) in dmesg
        VBIOS is inaccessible, it might help to restore it manually:
        $ ./fix_vbios.sh
    Sound issues, e.g. hda-codec: out of range cmd 3:0:5:707:ffffffbf in dmesg:
        Powering the NVIDIA gpu off also shuts down the audio output on it. This is pretty much ignored at the moment but didn't cause any major issues for me.
    Artefacts during lightdm/gnome-shell startup when using the nvidia card
        No idea, but I get the same artefacts without graphics switching