ubuntu-x-swat team mailing list archive

[Bryce Harrington <745112@xxxxxxxxxxxxxxxxxx>]

Roland, thanks for that.

Alright, here is what I think is happening.  Arrandale graphics cards
have a hardware limitation of a max texture buffer size of 4096x4096.
What this means is that compositing will work only if the total screen
width is 4096 or less.  Over that, and the GPU can lock up or other
weird things can occur.

My hypothesis is that when you are booting with the laptop docked, the
internal laptop LVDS panel is disabled, so your total width is 1920+1920
which is <4096.  However, when you boot with the laptop panel on and
*then* dock, the kernel is adding the two monitors to the left or right
of the laptop panel, resulting in 1920+1920+1440 which is >4096.

Looking at your monitors.xml, the first section shows HDMI2 and HDMI3
arranged side-by-side, and LVDS1 is also present and not disabled but
not set to any particular position, so it is unclear how the kernel
would position it in this case; perhaps it is adding it at +3840+0 which
would fit with my hypothesis.

There are a few things you could test which might prove my hypothesis
wrong:

a.  This behavior should occur only with Unity/Compiz.  If you boot
Classic Desktop (No Effects), the system freeze should be
unreproducible.  (However, see below)

b.  If in gnome-display-properties you arrange your LVDS to be
positioned *below* your two main monitors, it should work in unity.
Note you may need to delete your monitors.xml before making these
settings.

c.  If you disable your LVDS before docking (either using the GUI, or
via 'xrandr --output LVDS1 --off') and then docking, the system
shouldn't freeze.  (I don't know if the external monitors will fire up
in this case, but at least it won't trigger the freeze bug).

These may also give you some idea on working around the issue.

If those tests turn out correct, then this issue is basically a sub-case
of bug #555641.  However, I think that there could be some work done in
gnome-display-properties to check max texture size before enabling
configurations like this, if compiz is running.

Now, one other caveat.  It appears that there is a separate unrelated
bug that is common to Arrandale, that certain RANDR operations can
sometimes result in a monitor being improperly blanked.  So, that may
add some confusion to your testing.  But the way to tell these bugs
apart is that your original bug results in a system lockup (a black
screen with a mouse pointer, and no way to recover), whereas with this
latter blanking bug, you won't see a mouse cursor and the monitor will
appear to be not getting any signal.  Possibly you may be able to work
around this blanking issue via this command:

xset dpms force on

Anyway, sorry for the lengthy dissertation, but hopefully with this
information you can help me nail down this bug.  I have some thoughts on
what steps to take to get resolution to this issue (and the blanking
one) but let's see if you can prove my hypothesis before we get into all
that.

-- 
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https://bugs.launchpad.net/bugs/745112

Title:
  [arrandale] desktop is messed up (goes black) when laptop is docked
  with two external 1920x1200 monitors (x86_64)