Add some hopefully helpful notes about ACPI.

Approved by:	re (implicitly)
Reviewed by:	imp

release/doc/en_US.ISO8859-1/hardware/i386/proc-i386.sgml

@@ -65,4 +65,31 @@
     work around hardware bugs or other oddities.  When in doubt, a
     search of the archives of the &a.mobile; may be useful.</para>
 
+  <para>Most modern laptops (as well as many desktops) use the
+    Advanced Configuration and Power Management (ACPI) standard.  &os;
+    supports ACPI via the ACPI Component Architecture reference
+    implementation from Intel, as described in the &man.acpi.4; manual
+    page.  The use of ACPI causes instabilities on some machines and it
+    may be necessary to disable the ACPI driver, which is normally
+    loaded via a kernel module.  This may be accomplished by adding
+    the following line to <filename>/boot/loader.conf</filename>:</para>
+
+  <programlisting>hint.acpi.0.disabled="1"</programlisting>
+
+  <para>Users debugging ACPI-related problems may find it useful to
+    disable portions of the ACPI functionality.  The &man.acpi.4;
+    manual page has more information on how to do this via loader
+    tunables.</para>
+
+  <para>ACPI depends on a Differentiated System Descriptor Table
+    (DSDT) provided by each machine's BIOS.  Some machines have bad or
+    incomplete DSDTs, which prevents ACPI from functioning correctly.
+    Replacement DSDTs for some machines can be found at the <ulink
+    url="http://acpi.sourceforge.net/dsdt/index.php">DSDT</ulink>
+    section of the <ulink
+    url="http://acpi.sourceforge.net/">ACPI4Linux</ulink> project Web
+    site.  &os; can use these DSDTs to override the DSDT provided by
+    the BIOS; see the &man.acpi.4; manual page for more
+    information.</para>
+
 </sect1>