Nouveau

Nouveau is a reverse engineered free/open-source driver for nVidia chips. See Nouveau Feature Matrix for further details.

Kernel
You need at least -2.6.34. nouveau is a staging driver, so set CONFIG_STAGING=y, Enable Direct Rendering Manager (DRM) by setting CONFIG_DRM=y Select CONFIG_DRM_NOUVEAU=m.

The Direct Rendering Manager (DRM) and Kernel Modesetting drivers are a superset of the framebuffer system. You do not need to enable any framebuffer support, and in particular, DO NOT compile the rivafb (CONFIG_FB_RIVA) or nvidiafb (CONFIG_FB_NVIDIA) into the kernel. They may be compiled as modules if so desired, but they need to be blacklisted.

Build and install your kernel.

Nouveau and nvidia-drivers
If you have installed the in parallel, make sure that the   kernel module does not load before rebooting into your nouveau-enabled kernel.

If you still have an xorg.conf file with a Device section for the video card, change the Driver name:

Blacklisting other nvidia modules
There are a total of 4 different modules for nvidia cards: rivafb, nvidiafb, nvidia and nouveau. we need to blacklist everything except nouveau:

Adding module options
The nouveau module can take several options, but the most important is the modeset parameter. It can either be passed via modprobe.d or via the kernel command line: Or, on the kernel command line, append nouveau.modeset=1

Portage
Add nouveau to your VIDEO_CARDS in :

Reemerge to pull in. Reemerge to build the dri module for nouveau

Make sure that you are using the X11 implementation of OpenGL.

Genkernel
Remember to rebuild the initramfs so that the module options and blacklists are copied into the initramfs.

Phantom and unpopulated output connector issues
Sometimes the nouveau driver detects outputs that aren't really there (or output that do exist but aren't populated), and this can cause all kinds of problems. Phantom outputs can be disabled on the kernel command line. To figure out which output are detected, look in, they'll be listed in the form 'cardX-PORT-NUMBER', like card0-VGA-1. The part after cardX is the value of interest

To disable the output on the kernel command line, specify "video=PORT-NUMBER:d" for each output to be disable. So, if the kernel detects 3 outputs: VGA-1, TV-1, DVI-D-1, but only VGA-1 really exists, pass video=TV-1:d video=DVI-D-1:d to the kernel command line.

In addition, disable the output in X too. For each output, create a Monitor section, with an Identifier of the same name as the output, and add the line Option "Ignore" "True"  Continuing with the above example, xorg.conf would look as follows:

Machine locks up as soon as X starts
This is caused by problem with graphics acceleration. As a workaround, disable all acceleration: Or pass nouveau.noaccel=1 to the kernel command line.

Framebuffer is distorted, but X does not lock up
This is caused by a problem with the framebuffer acceleration. As a workaround, disable framebuffer acceleration only. Or pass nouveau.nofbaccel=1 to the kernel command line.

Syslog spammed with "Load detected on output X"
This can be caused by phantom outputs. If it a real output, upgrade to at least 0.9.9.

Framebuffer does not fill screen or is larger than screen
This can be caused by phantom outputs. Also try specifying the resolution for the desired output explicitly. For example VGA output with a desired resolution of 1280x1024, specify video=VGA-1:1280x1024.

*ERROR* failed to set mode on [CRTC:6] OR detected unhandled fb_set_par error, error code -22
Try the same fix for the "Framebuffer does not fill screen or is larger than screen"

If that does not work, make the xorg and framebuffer console resolution identical. So if the output is VGA-1 and the framebuffer resolution is 1280x1024, specify the following:

(EE) [drm] No DRICreatePCIBusID symbol
An error message stating (EE) [drm] No DRICreatePCIBusID symbol can be caused by a disabled dri module, i.e. if you have this configuration:

This can happen if you are switching from x11-drivers/nvidia-drivers. Change the Disable into a Load.

Additionally, this error can occur if using the wrong implementation of OpenGL.

Links

 * Official Nouveau Install Guide

Nouveau Nouveau