Configuring AGP

There are several choices for configuring the NVIDIA kernel module's use of AGP on Linux. You can choose to either use NVIDIA's builtin AGP driver (NvAGP), or the AGP driver that comes with the Linux kernel (AGPGART). This is controlled through the "NvAGP" option in your X config file:

Option "NvAGP" "0"  ... disables AGP support
    Option "NvAGP" "1"  ... use NvAGP, if possible
    Option "NvAGP" "2"  ... use AGPGART, if possible
    Option "NvAGP" "3"  ... try AGPGART; if that fails, try NvAGP

The default is 3 (the default was 1 until after 1.0-1251).

You should use the AGP driver that works best with your AGP chipset. If you are experiencing problems with stability, you may want to start by disabling AGP and seeing if that solves the problems. Then you can experiment with the AGP driver configuration.

You can query the current AGP status at any time via the /proc filesystem interface (see Appendix M, Proc Interface).

To use the Linux 2.4 AGPGART driver, you will need to compile it with your kernel and either statically link it in, or build it as a module and load it. To use the Linux 2.6 AGPGART driver, both the AGPGART frontend module, apggart.ko, and the backend module for your AGP chipset (nvidia-agp.ko, intel-agp.ko, via-agp.ko, ...) need to be statically linked into the kernel, or built as modules and loaded.

NVIDIA's builtin AGP support is unavailable if an AGPGART backend driver is loaded into the kernel. On Linux 2.4, it is recommended that you compile AGPGART as a module and make sure that it is not loaded when trying to use NVIDIA's AGP driver. On Linux 2.6, the agpgart.ko frontend module will always be loaded, as it is used by the NVIDIA kernel module to determine if an AGPGART backend module is loaded. When the NVIDIA AGP driver is to be used on a Linux 2.6 system, it is recommended that you make sure the AGPGART backend drivers are built as modules and that they are not loaded.

Please also note that changing AGP drivers generally requires a reboot before the changes actually take effect.

If you are using a recent Linux 2.6 kernel that has the Linux AGPGART driver statically linked in (some distribution kernels do), you can pass the

agp=off

parameter to the kernel (via LILO or GRUB, for example) to disable AGPGART support. As of Linux 2.6.11, most AGPGART backend drivers should respect this parameter.