Enabling Randr12 support in nouveau

Randr 1.2 is used by Nouveau. No need to explicitly enable it, and you cannot disable it.

Generic HowTos

Dual Head setup


Sections and configuration settings to remove

Randr 1.2 does not use multiple Screen sections, so if you have those you have to remove them from your xorg.conf :

  • If you have two sections like these, remove one of these sections (in this example Screen1):

    Section "Screen"
        Identifier     "Screen0"
    Section "Screen"               <==== Remove this second section, if you have sone (start removing lines here)
        Identifier     "Screen1"
    EndSection                     (stop removing lines here)
  • If you have a Option "MonitorLayout" or/and "Screen" options in the Device section, remove them

  • Also remove the second Screen entry from the ServerLayout section. Example :

    Screen      0  "Screen0" 1680 0
    Screen      1  "Screen1" LeftOf "Screen0" <= remove this one (for Screen1)
  • Also remove any RightOf/LeftOf indications from the remaining Screen line in the ServerLayout section (see above)

Settings on xorg.conf for Randr12

Note that with today's software you often don't need a xorg.conf file at all for nouveau and dual-head to work.

If you do not preconfigure a left/right/above/below setup in your xorg.xonf (see next section) add Virtual x y to your Display Section:

Section "Screen"
  Identifier   "Your Screen identifier here"
  DefaultDepth 24
  SubSection "Display"
    Depth      24
    Virtual 3360 1050
  Device       "Your Device identifier here"

The example above configures a framebuffer for two monitors, each using resolutions up to 1680x1050 pixels, put side-by-side dynamically, after you started X. The values are calculated like this:

Virtual <width of the two monitors, e.g. 1680+1680=3360> <maxium height to used by the montiors, e.g. 1050>

Only the part which the monitors show is used: You can start and use X with one monitor as ususal but later add a new monitor and use xrandr with --leftof or --rightof to place the new monitor left or right of your primary monitor.

Preconfigured side-by-side (LeftOf/RightOf) setup thru xorg.conf

If you have done the above, you can also preconfigure the two monitors to be side-by-side right from the X startup. With this, you do not even need the "Virtual " line because then, the X server already knows before starting that it has to allocate a virtual framebuffer which fits both Monitors side-by-side.

You need to make the following changes for this to work (simplest way):

  • Change the Monitor identifiers in your xorg.conf to the identifiers which "xrandr" reports and add a LeftOf/RightOf to one of the Monitor sections. Example:

    Section "Monitor"
      Identifier   "DVI-D-0"
    Section "Monitor"
      Identifier   "VGA-0"
      Option "LeftOf" "DVI-D-0"

Then restart X and enjoy :-)

Examples for the usage of the Xorg xrandr tool to manipulate the monitor setup

Usage: xrandr -h gives a short list of available options, man xrandr shows you the xrandr manual.

When Randr12 is enabled, you can check the current Randr12 configuration with with xrandr -q (or no options):

xrandr -q
Screen 0: minimum 320 x 200, current 2960 x 1050, maximum 3000 x 1050
DVI-A-0 disconnected (normal left inverted right x axis y axis)
DVI-D-0 connected 1680x1050+0+0 (normal left inverted right x axis y axis) 474mm x 296mm
   1680x1050      60.0*+
   1280x1024      75.0     59.9
   1280x960       59.9
   1152x864       75.0     74.8
   1024x768       75.1     70.1     60.0
   832x624        74.6
   800x600        72.2     75.0     60.3     56.2
   640x480        75.0     72.8     66.7     60.0
   720x400        70.1
VGA-0 connected 1280x1024+1680+0 (normal left inverted right x axis y axis) 350mm x 262mm
   1280x1024      84.8*    75.0
   1152x864       75.0
   1024x768       84.9     75.1     70.1     60.0     59.9     43.5
   832x624        74.6
   800x600        84.9     72.2     75.0     60.3     56.2
   640x480        84.6     75.0     72.8     74.8     66.7     60.0
   720x405        69.6
   720x400        87.8     70.1

Change the mode of an output using:

xrandr --output <output>  --mode <mode to switch to>

To turn a newly connected monitor on, use

xrandr --output <display>  --auto


xrandr --output <output>  --mode ...x...

To turn an output off:

xrandr --output <output>  --off

To make an output show the same screen area as an other output (cloned mode, default with Randr12):

xrandr --output <output to change> --same-as <output you want to clone>

To put the display of one output left, right, above or below to the display of an existing output use --left-of, --right-of, --above, --below :

xrandr --output <output to change> [ --left-of |--right-of | --above | --below ] <output which shall keep its position>

More xrandr examples are found in the generic Randr12 howtos mentioned on the top of this page.