From 1b17b3b915fce00a1273a9b7247a4ebfb89a4d1d Mon Sep 17 00:00:00 2001
From: rnhmjoj <rnhmjoj@inventati.org>
Date: Mon, 22 Jun 2020 01:35:00 +0200
Subject: [PATCH] nixos/doc: add section on Intel DDX drivers

---
 nixos/doc/manual/configuration/x-windows.xml | 41 ++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/nixos/doc/manual/configuration/x-windows.xml b/nixos/doc/manual/configuration/x-windows.xml
index 110712baf5f..ca93026d865 100644
--- a/nixos/doc/manual/configuration/x-windows.xml
+++ b/nixos/doc/manual/configuration/x-windows.xml
@@ -96,6 +96,47 @@
   The options are named identically for all other display managers.
   </para>
  </simplesect>
+ <simplesect xml:id="sec-x11--graphics-cards-intel">
+  <title>Intel Graphics drivers</title>
+  <para>
+   There are two choices for Intel Graphics drivers in X.org:
+   <literal>modesetting</literal> (included in the <package>xorg-server</package> itself)
+   and <literal>intel</literal> (provided by the package <package>xf86-video-intel</package>).
+  </para>
+  <para>
+   The default and recommended is <literal>modesetting</literal>.
+   It is a generic driver which uses the kernel
+   <link xlink:href="https://en.wikipedia.org/wiki/Mode_setting">mode setting</link>
+   (KMS) mechanism. It supports Glamor (2D graphics acceleration via OpenGL)
+   and is actively maintained but may perform worse in some cases (like in old chipsets).
+  </para>
+  <para>
+   The second driver, <literal>intel</literal>, is specific to Intel GPUs,
+   but not recommended by most distributions: it lacks several modern features
+   (for example, it doesn't support Glamor) and the package hasn't been officially
+   updated since 2015.
+  </para>
+  <para>
+   The results vary depending on the hardware, so you may have to try both drivers.
+   Use the option <xref linkend="opt-services.xserver.videoDrivers"/> to set one.
+   The recommended configuration for modern systems is:
+<programlisting>
+  <xref linkend="opt-services.xserver.videoDrivers"/> = [ "modesetting" ];
+  <xref linkend="opt-services.xserver.useGlamor"/> = true;
+</programlisting>
+   If you experience screen tearing no matter what, this configuration was
+   reported to resolve the issue:
+<programlisting>
+  <xref linkend="opt-services.xserver.videoDrivers"/> = [ "intel" ];
+  <xref linkend="opt-services.xserver.deviceSection"/> = ''
+    Option "DRI" "2"
+    Option "TearFree" "true"
+  '';
+</programlisting>
+   Note that this will likely downgrade the performance compared to
+  <literal>modesetting</literal> or <literal>intel</literal> with DRI 3 (default).
+  </para>
+ </simplesect>
  <simplesect xml:id="sec-x11-graphics-cards-nvidia">
   <title>Proprietary NVIDIA drivers</title>
   <para>