Comment 11 for bug 980058

OK, so I've made a discovery in terms of what could be causing this problem, it appears that when the display is garbled, it's because vesafb is being used, rather than the intel driver. attached it the relevant dmsg that i got by sshing into the computer, note the following lines when the graphics are garbled:

Dmesg when the display is garbled:
...
[ 21.024313] mtrr: type mismatch for b0000000,10000000 old: write-back new: write-combining
[ 21.024320] [drm] MTRR allocation failed. Graphics performance may suffer.
[ 21.025526] i915 0000:00:02.0: irq 42 for MSI/MSI-X
[ 21.025540] [drm] Supports vblank timestamp caching Rev 1 (10.10.2010).
[ 21.025546] [drm] Driver supports precise vblank timestamp query.
[ 21.025612] vgaarb: device changed decodes: PCI:0000:00:02.0,olddecodes=io+mem,decodes=io+mem:owns=io+mem
...
[ 22.471389] vesafb: mode is 1024x768x32, linelength=4096, pages=0
[ 22.471392] vesafb: scrolling: redraw
[ 22.471394] vesafb: Truecolor: size=8:8:8:8, shift=24:16:8:0
...
[ 22.472177] vesafb: framebuffer at 0xb0000000, mapped to 0xffffc90011500000, using 3072k, total 3072k
[ 22.472350] Console: switching to colour frame buffer device 128x48
[ 22.472378] fb0: VESA VGA frame buffer device
...
Xorg.log when the display is garbled (contains loads of lines e.g.):
...
[ 22.579] (II) VESA(0): Total Memory: 2047 64KB banks (131008kB)
[ 22.579] (II) VESA(0): <default monitor>: Using hsync value of 47.05 kHz
[ 22.579] (II) VESA(0): <default monitor>: Using vrefresh value of 60.01 Hz
...

compared to when inteldrmfb is used (the following was taken from this boot, when the display was behaving normally):
Dmesg when the problem isn't present:
...
[ 21.472059] mtrr: type mismatch for b0000000,10000000 old: write-back new: write-combining
[ 21.472064] [drm] MTRR allocation failed. Graphics performance may suffer.
[ 21.472579] i915 0000:00:02.0: irq 42 for MSI/MSI-X
[ 21.472584] [drm] Supports vblank timestamp caching Rev 1 (10.10.2010).
[ 21.472589] [drm] Driver supports precise vblank timestamp query.
[ 21.472675] vgaarb: device changed decodes: PCI:0000:00:02.0,olddecodes=io+mem,decodes=io+mem:owns=io+mem
...
[ 22.091428] fbcon: inteldrmfb (fb0) is primary device
[ 22.091963] Console: switching to colour frame buffer device 170x48
[ 22.091998] fb0: inteldrmfb frame buffer device
[ 22.092000] drm: registered panic notifier
[ 22.095748] input: Video Bus as /devices/LNXSYSTM:00/device:00/PNP0A08:00/LNXVIDEO:00/input/input7
[ 22.095845] ACPI: Video Device [GFX0] (multi-head: yes rom: no post: no)
[ 22.097115] [drm] Initialized i915 1.6.0 20080730 for 0000:00:02.0 on minor 0
...

Xorg.log when the problem isn't present:
...
[ 5137.691] (==) intel(0): Depth 24, (--) framebuffer bpp 32
[ 5137.691] (==) intel(0): RGB weight 888
[ 5137.691] (==) intel(0): Default visual is TrueColor
[ 5137.691] (II) intel(0): Integrated Graphics Chipset: Intel(R) Sandybridge Mobile (GT2)
[ 5137.691] (--) intel(0): Chipset: "Sandybridge Mobile (GT2)"
...

What would cause vesafb to be used instead of inteldrmfb?