Kernel 3.16 with MST support for Debian experimental

on September 6, 2014

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Mendix recently gave me a ThinkPad T440s. This is an amazing machine, however, to use more than one external display through a docking station or through the mini-displayport connector you have to use DisplayPort Multi Stream Transport (MST). If you’re on Windows this is no problem (I assume), but on Linux you’re out of luck for now. While support has been built by David Airlie of Red Hat, it has yet to appear in a stable kernel (3.17 will include the changes) and only a couple distributions included it so far. In this post I’ll show you how I got it to run on Debian testing with kernel from experimental, that I patched using David Airlie’s Linux repository.

We’ll follow this how-to from wiki.debian.org but skip some steps.


Preparation

Start with a fully upgraded Debian system: sudo apt-get dist-upgrade.

Start fetching the linux kernel from a location that has the necessary changes: git clone git://people.freedesktop.org/~airlied/linux

Obtain the packages needed to compile the kernel: sudo apt-get install devscripts equivs wget fakeroot build-essential libncurses5-dev


Installing a kernel from experimental

So, here is what I was running so far: Debian testing with kernel 3.16 from experimental. To do this, you need to include these lines in your /etc/apt/sources.list

deb http://ftp.nl.debian.org/debian/ experimental main non-free contrib
deb-src http://ftp.nl.debian.org/debian/ experimental main non-free contrib

To prevent that all your packages are upgraded to the wild wild west of Debian experimental you need to create a pin in a file like /etc/apt/preferences.d/no-experimental-please the contents:

Package: *
Pin: release a=experimental
Pin-Priority: 50

This ensures that everything from experimental gets a lower priority, so it won’t be installed. Verify that the pin works and you won’t upgrade everything by running a dry-run dist-upgrade: apt-get dist-upgrade -s.

Now run apt-get update and search for the newest kernel packages (3.16 at this time):

$ apt-cache search 3.16 | grep ^linux
...
linux-headers-3.16-trunk-amd64
...
linux-image-3.16-trunk-amd64
...

We’re going to install the kernel image and the header files: sudo apt-get install linux-headers-3.16-trunk-amd64 linux-image-3.16-trunk-amd64

Now we have a fancy new kernel, but we need to apply some patches!


Getting a patch ready

Go to the directory you’ve cloned the linux kernel in and run git checkout drm-i915-mst-v3.16. You can see that David neatly rebased his changes on top of the 3.16 release, so we can get a patch ready with git diff v3.16..drm-i915-mst-v3.16 > ~/mst-patch-on-3.16.


Getting the kernel source and applying the patch

Now we’re going to a new directory and get the source of the debian linux kernel: apt-get source linux. Verify that this version matches the kernel you we’re trying to patch.

Run the following:

cd linux-*
sudo apt-get build-dep linux
sed -i -e 's/^abiname:.*/&+mst.1/' debian/config/defines  # change the name of the packages so they don't clash with the system packages
quilt new mst-patch
for i in $(patch -p1 --dry-run < ~/mst-patch-on-3.16 | cut -d' ' -f3); do quilt add $i; done
patch -p1 < ~/mst-patch-on-3.16
quilt refresh
make -f debian/rules source  # fails the first time
make -f debian/rules source
dch --local +mst.1

Now write a fancy changelog for this patch, mine looked like this:

linux (3.16-1~exp1+mst.1) UNRELEASED; urgency=medium

  * Add displayport mst patch from http://cgit.freedesktop.org/~airlied

 -- Jouke Waleson <jouke@waleson.com>  Sat, 06 Sep 2014 19:49:22 +0200

This will be added to the file debian/changelog

Now we’re going to build this kernel for one platform only.

fakeroot make -f debian/rules.gen setup_amd64_none_amd64
fakeroot make -f debian/rules.gen binary-arch_amd64_none_amd64 binary-indep -j$(nproc)

A long wait later (30 minutes on my system) you will have a couple of .deb files, install the required ones:

sudo dpkg -i linux-headers-3.16-trunk+mst.1-amd64_3.16-1~exp1+mst.1_amd64.deb linux-headers-3.16-trunk+mst.1-common_3.16-1~exp1+mst.1_amd64.deb linux-image-3.16-trunk+mst.1-amd64_3.16-1~exp1+mst.1_amd64.deb

If everything went right so far, you can now reboot and choose this kernel in grub!

Here is the output from xrandr after rebooting:

$ xrandr
Screen 0: minimum 8 x 8, current 5520 x 1080, maximum 32767 x 32767
eDP1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 309mm x 173mm
   1920x1080     60.05*+  59.93  
   1680x1050     59.95    59.88  
   1600x1024     60.17  
   1400x1050     59.98  
   1280x1024     60.02  
   1440x900      59.89  
   1280x960      60.00  
   1360x768      59.80    59.96  
   1152x864      60.00  
   1024x768      60.00  
   800x600       60.32    56.25  
   640x480       59.94  
DP1 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
DP2 disconnected (normal left inverted right x axis y axis)
HDMI2 disconnected (normal left inverted right x axis y axis)
DP3 disconnected (normal left inverted right x axis y axis)
DP4 connected 1920x1080+1920+0 (normal left inverted right x axis y axis) 531mm x 299mm
   1920x1080     60.00*+  50.00    59.94  
   1600x1200     60.00  
   1680x1050     59.88  
   1280x1024     75.02    60.02  
   1440x900      74.98    59.90  
   1280x960      60.00  
   1280x800      59.91  
   1152x864      75.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.08    70.07    60.00  
   832x624       74.55  
   800x600       72.19    75.00    60.32    56.25  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    72.81    66.67    60.00    59.94  
   720x400       70.08  
DP5 connected 1680x1050+3840+0 (normal left inverted right x axis y axis) 459mm x 296mm
   1680x1050     59.88*+
   1280x1024     75.02    60.02  
   1280x960      60.00  
   1152x864      75.00  
   1024x768      75.08    70.07    60.00  
   832x624       74.55  
   800x600       72.19    75.00    60.32    56.25  
   640x480       75.00    72.81    66.67    60.00  
   720x400       70.08  
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

Great success, epic win, etcetera.

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About Jouke Waleson

Product Manager and Team Lead of the Mendix Cloud team.

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