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<h2 class="title"><a name="configuringagp" id=
"configuringagp"></a>Chapter 12. Configuring AGP</h2>
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<p>There are several choices for configuring the NVIDIA kernel
module's use of AGP on Linux. You can choose to either use the
NVIDIA 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:</p>
<pre class="screen">
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
</pre>
<p>The default is 3 (the default was 1 until after 1.0-1251).</p>
<p>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.</p>
<p>You can query the current AGP status at any time via the
<code class="filename">/proc</code> filesystem interface (see
<a href="chapter-21.html" title=
"Chapter 21. Using the Proc Filesystem Interface">Chapter 21,
<i>Using the Proc Filesystem Interface</i></a>).</p>
<p>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, <code class="filename">apggart.ko</code>,
and the backend module for your AGP chipset (<code class=
"filename">nvidia-agp.ko</code>, <code class=
"filename">intel-agp.ko</code>, <code class=
"filename">via-agp.ko</code>, ...) need to be statically linked
into the kernel, or built as modules and loaded.</p>
<p>NVIDIA 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 the NVIDIA AGP driver. On Linux 2.6, the
<code class="filename">agpgart.ko</code> 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.</p>
<p>Also note that changing AGP drivers generally requires a reboot
before the changes actually take effect.</p>
<p>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</p>
<pre class="screen">
agp=off
</pre>
<p>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.</p>
<p>The following AGP chipsets are supported by the NVIDIA AGP
driver; for all other chipsets it is recommended that you use the
AGPGART module.</p>
<div class="informaltable">
<table summary="(no summary available)" border="0">
<colgroup>
<col></colgroup>
<thead>
<tr>
<th>Supported AGP Chipsets</th>
</tr>
</thead>
<tbody>
<tr>
<td>Intel 440LX</td>
</tr>
<tr>
<td>Intel 440BX</td>
</tr>
<tr>
<td>Intel 440GX</td>
</tr>
<tr>
<td>Intel 815 ("Solano")</td>
</tr>
<tr>
<td>Intel 820 ("Camino")</td>
</tr>
<tr>
<td>Intel 830M</td>
</tr>
<tr>
<td>Intel 840 ("Carmel")</td>
</tr>
<tr>
<td>Intel 845 ("Brookdale")</td>
</tr>
<tr>
<td>Intel 845G</td>
</tr>
<tr>
<td>Intel 850 ("Tehama")</td>
</tr>
<tr>
<td>Intel 855 ("Odem")</td>
</tr>
<tr>
<td>Intel 860 ("Colusa")</td>
</tr>
<tr>
<td>Intel 865G ("Springdale")</td>
</tr>
<tr>
<td>Intel 875P ("Canterwood")</td>
</tr>
<tr>
<td>Intel E7205 ("Granite Bay")</td>
</tr>
<tr>
<td>Intel E7505 ("Placer")</td>
</tr>
<tr>
<td>AMD 751 ("Irongate")</td>
</tr>
<tr>
<td>AMD 761 ("IGD4")</td>
</tr>
<tr>
<td>AMD 762 ("IGD4 MP")</td>
</tr>
<tr>
<td>AMD 8151 ("Lokar")</td>
</tr>
<tr>
<td>VIA 8371</td>
</tr>
<tr>
<td>VIA 82C694X</td>
</tr>
<tr>
<td>VIA KT133</td>
</tr>
<tr>
<td>VIA KT266</td>
</tr>
<tr>
<td>VIA KT400</td>
</tr>
<tr>
<td>VIA P4M266</td>
</tr>
<tr>
<td>VIA P4M266A</td>
</tr>
<tr>
<td>VIA P4X400</td>
</tr>
<tr>
<td>VIA K8T800</td>
</tr>
<tr>
<td>VIA K8N800</td>
</tr>
<tr>
<td>VIA PT880</td>
</tr>
<tr>
<td>VIA KT880</td>
</tr>
<tr>
<td>RCC CNB20LE</td>
</tr>
<tr>
<td>RCC 6585HE</td>
</tr>
<tr>
<td>Micron SAMDDR ("Samurai")</td>
</tr>
<tr>
<td>Micron SCIDDR ("Scimitar")</td>
</tr>
<tr>
<td>NVIDIA nForce</td>
</tr>
<tr>
<td>NVIDIA nForce2</td>
</tr>
<tr>
<td>NVIDIA nForce3</td>
</tr>
<tr>
<td>ALi 1621</td>
</tr>
<tr>
<td>ALi 1631</td>
</tr>
<tr>
<td>ALi 1647</td>
</tr>
<tr>
<td>ALi 1651</td>
</tr>
<tr>
<td>ALi 1671</td>
</tr>
<tr>
<td>SiS 630</td>
</tr>
<tr>
<td>SiS 633</td>
</tr>
<tr>
<td>SiS 635</td>
</tr>
<tr>
<td>SiS 645</td>
</tr>
<tr>
<td>SiS 646</td>
</tr>
<tr>
<td>SiS 648</td>
</tr>
<tr>
<td>SiS 648FX</td>
</tr>
<tr>
<td>SiS 650</td>
</tr>
<tr>
<td>SiS 651</td>
</tr>
<tr>
<td>SiS 655</td>
</tr>
<tr>
<td>SiS 655FX</td>
</tr>
<tr>
<td>SiS 661</td>
</tr>
<tr>
<td>SiS 730</td>
</tr>
<tr>
<td>SiS 733</td>
</tr>
<tr>
<td>SiS 735</td>
</tr>
<tr>
<td>SiS 745</td>
</tr>
<tr>
<td>SiS 755</td>
</tr>
<tr>
<td>ATI RS200M</td>
</tr>
</tbody>
</table>
</div>
<p></p>
<p>If you are experiencing AGP stability problems, you should be
aware of the following:</p>
<div class="variablelist">
<p class="title"><b>Additional AGP Information</b></p>
<p>On Athlon motherboards with the VIA KX133 or 694X chip set, such
as the ASUS K7V motherboard, NVIDIA drivers default to AGP 2x mode
to work around insufficient drive strength on one of the signals.
You can force AGP 4x by setting NVreg_EnableVia4x to 1. Note that
this may cause the system to become unstable.</p>
<dl>
<dt><span class="term">Support for the processor's Page Size
Extension on Athlon Processors</span></dt>
<dd>
<p>Some Linux kernels have a conflicting cache attribute bug that
is exposed by advanced speculative caching in newer AMD Athlon
family processors (AMD Athlon XP, AMD Athlon 4, AMD Athlon MP, and
Models 6 and above AMD Duron). This kernel bug usually shows up
under heavy use of accelerated 3D graphics with an AGP graphics
card.</p>
<p>Linux distributions based on kernel 2.4.19 and later *should*
incorporate the bug fix, but older kernels require help from the
user in ensuring that a small portion of advanced speculative
caching is disabled (normally done through a kernel patch) and a
boot option is specified in order to apply the whole fix.</p>
<p>NVIDIA's driver automatically disables the small portion of
advanced speculative caching for the affected AMD processors
without the need to patch the kernel; it can be used even on
kernels which do already incorporate the kernel bug fix.
Additionally, for older kernels the user performs the boot option
portion of the fix by explicitly disabling 4MB pages. This can be
done from the boot command line by specifying:</p>
<pre class="screen">
mem=nopentium
</pre>
<p>Or by adding the following line to /etc/lilo.conf:</p>
<pre class="screen">
append = "mem=nopentium"
</pre>
<p></p>
</dd>
<dt><span class="term">AGP Rate</span></dt>
<dd>
<p>You may want to decrease the AGP rate setting if you are seeing
lockups with the value you are currently using. You can do so by
extracting the <code class="filename">.run</code> file:</p>
<pre class="screen">
# sh NVIDIA-Linux-x86_64-173.14.31-pkg1.run --extract-only
# cd NVIDIA-Linux-x86_64-173.14.31-pkg1/usr/src/nv/
</pre>
<p>Then edit nv-reg.h, and make the following changes:</p>
<pre class="screen">
- NV_DEFINE_REG_ENTRY(__NV_REQ_AGP_RATE, 15);
+ NV_DEFINE_REG_ENTRY(__NV_REQ_AGP_RATE, 4); /* force AGP Rate to 4x */
</pre>
<p>or</p>
<pre class="screen">
+ NV_DEFINE_REG_ENTRY(__NV_REQ_AGP_RATE, 2); /* force AGP Rate to 2x */
</pre>
<p>or</p>
<pre class="screen">
+ NV_DEFINE_REG_ENTRY(__NV_REQ_AGP_RATE, 1); /* force AGP Rate to 1x */
</pre>
<p>Then recompile and load the new kernel module. To do this, run
<code class="filename">nvidia-installer</code> with the
<code class="option">-n</code> command line option:</p>
<pre class="screen">
# cd ../../..; ./nvidia-installer -n
</pre>
<p></p>
</dd>
<dt><span class="term">AGP drive strength BIOS setting (Via-based
motherboards)</span></dt>
<dd>
<p>Many Via-based motherboards allow adjusting the AGP drive
strength in the system BIOS. The setting of this option largely
affects system stability, the range between 0xEA and 0xEE seems to
work best for NVIDIA hardware. Setting either nibble to 0xF
generally results in severe stability problems.</p>
<p>If you decide to experiment with this, you need to be aware of
the fact that you are doing so at your own risk and that you may
render your system unbootable with improper settings until you
reset the setting to a working value (w/ a PCI graphics card or by
resetting the BIOS to its default values).</p>
</dd>
<dt><span class="term">System BIOS version</span></dt>
<dd>
<p>Make sure you have the latest system BIOS provided by the
motherboard manufacturer.</p>
<p>On ALi1541 and ALi1647 chipsets, NVIDIA drivers disable AGP to
work around timing and signal integrity problems. You can force AGP
to be enabled on these chipsets by setting NVreg_EnableALiAGP to 1.
Note that this may cause the system to become unstable.</p>
<p>Early system BIOS revisions for the ASUS A7V8X-X KT400
motherboard misconfigure the chipset when an AGP 2.x graphics card
is installed; if X hangs on your ASUS KT400 system with either
Linux AGPGART or NvAGP enabled and the installed graphics card is
not an AGP 8x device, make sure that you have the latest system
BIOS installed.</p>
</dd>
</dl>
</div>
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