services: xorg: Allow users to specify the drivers to use.

* gnu/services/xorg.scm (xorg-start-command): Add #:drivers parameter.
  Add 'device-section' procedure, and use it in 'xserver.conf'.
* doc/guix.texi (X Window): Document it.

1 files changed, 9 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 4a596bcbf3..3fbe963967 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -3953,6 +3953,15 @@ password.  When @var{auto-login?} is true, log in automatically as
 @var{default-user}.
 @end deffn
 
+@deffn {Monadic Procedure} xorg-start-command [#:guile] @
+  [#:drivers '()] [#:xorg-server @var{xorg-server}]
+Return a derivation that builds a @var{guile} script to start the X server
+from @var{xorg-server}.  Usually the X server is started by a login manager.
+
+@var{drivers} must be either the empty list, in which case Xorg chooses a
+graphics driver automatically, or a list of driver names that will be tried in
+this order---e.g., @code{("modesetting" "vesa")}.
+@end deffn
 
 @node Setuid Programs
 @subsection Setuid Programs