Only fallback mode with kernel 3.16

[Jan Niggemann <jn hz6 de>]

Hi list,

I'm currently looking into a weird behavior with GNOME 3 starting in 
fallback mode every now and then.
I only experience this issue with the latest 3.16 kernel, I suspect an 
issue with my graphics driver.
There are no issues using 3.14.18 instead, perhaps there's less video 
RAM available when running kernel 3.16...

To debug, I need to know when, why GNOME starts in fallback mode (using 
llvmpipe).

Debian stable, 32bit, Lenovo T400
GNOME Shell 3.4.2

laptop:~$ grep Mem /var/log/Xorg.0.log
[     8.975] (--) PCI:*(0:0:2:0) 8086:2a42:17aa:20e4 rev 7, Mem @ 
0xf4400000/4194304, 0xd0000000/268435456, I/O @ 0x00001800/8
[     8.975] (--) PCI: (0:0:2:1) 8086:2a43:17aa:20e4 rev 7, Mem @ 
0xf4200000/1048576

laptop:~$ lspci |grep 02\.
00:02.0 VGA compatible controller: Intel Corporation Mobile 4 Series 
Chipset Integrated Graphics Controller (rev 07)
00:02.1 Display controller: Intel Corporation Mobile 4 Series Chipset 
Integrated Graphics Controller (rev 07)

Thank you in advance
jan