Dual Head on Ubuntu Hardy with Intel GM965 (Part 1)

Yesterday I got a LCD monitor that I plugged in to the docking station of my Dell D830. Using cloned mode where both the laptop display and the external monitor display the same, worked right away. But I wanted to use extended mode so that I can have a bigger workspace. Here’s how I got it to work.

I tried to change it through the Monitor Resolution Settings dialog (System/Preferences/Screen Resolution), but it didn’t work.

There are several places on the web that explain how you can set this up, but none of them really works with Compiz. Then I found a bug report that contained the solution: The driver for i965 has a bug that limits the screen size to 2048×2048.

Here is what I did:

1. Patching

$ apt-get source xserver-xorg-video-intel
$ cd xserver-xorg-video-intel-2.2.1


Then I changed the file src/i965_render.c and applied the following patch:
http://gitweb.freedesktop.org/?p=xorg/driver/xf86-video-intel.git;a=blobdiff;h=ada3919adf33179ab72aecfdc2e9e48c439f8888;hp=7f798e6c8dfb0a5775cae5d4e6595d8d09b2a251;hb=4f5500abe209b92b39ae1f2d7a1118362ac95034;f=src/i965_render.c

The diff for this file is

- if ((w > 0x7ff) || (h > 0x7ff))
+ if ((w > 8192) || (h > 8192))

This enables support for larger resolutions (8192×8192).

Then I edited the file debian/changelog and added a new entry with a new version number (I choose 2:2.2.1-1ubuntu13.6-1) at the top of the file (so that apt knows the package I’m going to create is newer than the currently installed package, otherwise it might decide to reinstall the unpatched version from the official repository). I built the package:

$ dpkg-buildpackage -rfakeroot -uc -b

and installed it:

$ sudo dpkg -i ../xserver-xorg-video-intel_2.2.1-1ubuntu13.6-1_amd64.deb

In addition the Mesa driver also needs to be modified:

$ cd ..
$ apt-get source mesa
$ cd mesa-7.0.3-rc2

I patched the file src/mesa/drivers/dri/i965/brw_context.c with the following patch (also taken from the bug report):

diff --git a/src/mesa/drivers/dri/i965/brw_context.c b/src/mesa/drivers/dri/i965/brw_c!
index 1601f6d..c06f5da 100644
--- a/src/mesa/drivers/dri/i965/brw_context.c
+++ b/src/mesa/drivers/dri/i965/brw_context.c
@@ -138,10 +138,10 @@ GLboolean brwCreateContext( const __GLcontextModes *mesaVis,
/* Advertise the full hardware capabilities. The new memory
* manager should cope much better with overload situations:
*/
- ctx->Const.MaxTextureLevels = 12;
+ ctx->Const.MaxTextureLevels = 13;
ctx->Const.Max3DTextureLevels = 9;
ctx->Const.MaxCubeTextureLevels = 12;
- ctx->Const.MaxTextureRectSize = (1<<11);
+ ctx->Const.MaxTextureRectSize = (1<<12);
ctx->Const.MaxTextureUnits = BRW_MAX_TEX_UNIT;

/* ctx->Const.MaxNativeVertexProgramTemps = 32; */

Again I edited the file debian/changelog and built the package:

$ dpkg-buildpackage -rfakeroot -uc -b

I installed only those packages that I already had installed. To verify that larger resolutions are possible now I did a

$ glxinfo -l | grep GL_MAX_TEXTURE_SIZE

which gave me

GL_MAX_TEXTURE_SIZE = 4096

The 4096 is a general limit in Mesa, but it is enough to run my external LCD monitor and my laptop screen with 1680×1050 each.

Changing Settings

I also had to modify my xorg.conf: in the section “Screen” I added a new subsection “Display”:

SubSection "Display"
Virtual 4096 4096
EndSubSection

After that I tried to get the expanded mode to work – no success. However, this morning after having rebooted it suddenly worked:

Doing a xrandr displays the names of the output ports and the possible screen resolutions. Then I did a

$ xrandr --output TMDS-1 --left-of LVDS

and it worked!