Intel

intel is the open source graphics driver for Intel GMA onboard graphics cards, starting with the Intel 810.

Hardware detection
To choose the right driver, first detect the graphics card. You can use lspci for this task:

Feature support

 * 1) Needs testing packages: >=mesa-9.1
 * 2) A FOSS implementation is in development under the name Beignet

Kernel
You need to activate the following kernel options:

Driver
Portage uses the variable VIDEO_CARDS for enabling support for various graphics cards in packages. Setting VIDEO_CARDS to e.g. intel (see the feature matrix) will pull in the correct driver:

Check the USE flags of :

After setting this you want to update your system so the changes take effect:

VAAPI
Intel GMA X4500HD / G45 / GM45 and newer supports VAAPI hardware video acceleration.

xorg.conf
The X server is designed to work out-of-the-box, with no need to manually edit X.Org's configuration files. It should detect and configure devices such as displays, keyboards, and mice.

However, the main configuration file of the X server is the xorg.conf.

Troubleshooting

 * Guide, how to report bugs upstream
 * Guide, how to report bugs upstream
 * Guide, how to report bugs upstream
 * Guide, how to report bugs upstream

KDM freezes
A workaround is to set TerminateServer=true in all sections of the file, which starts with X-.

Black screen
According to this Debian wiki, CONFIG_FRAMEBUFFER_CONSOLE must be set to y (aka built-in). Otherwise, it is possible to always have a black screen unless nomodeset is passed to the kernel, thus disabling KMS.

External resources

 * X.Org Wiki