Linux console goes crazy ("cpu pipe a fifo underrun") when Xorg quits.

Question

Hi,
>> Short story:
When I run `startx', it works alright, it runs the `twm' window manager. When I quit twm, however, the display starts behaving like an old TV with a bad signal. I took a picture:
>> Long story:
I installed Arch on a new DELL Inspiron and, following the wiki ([1] and [2]), installed:
xorg-server
xf86-video-intel
mesa-libgl
libva-intel-driver
libva
libvdpau-va-gl
My xinitrc is ends with:
exec ~/.tdm/sessions/TWM
which in turn exec's the following script:
#!/bin/sh
twm &
xterm -fg white -bg black &
exec xmessage "Exit"
So far so good; I log in, run `startx', and when I quit the `twm' window manager, havoc starts (see the "short story" above hehe). In the above "screenshot" you can see that the display shows the console in "three times" in the same display, each of the three overlapping each other, and all of them blurry, etc. But I can still type, and everything appears to be working alright, except for the display. Sometimes, when the display stops blinking for a second, I can read the kernel message invading my bash prompt:
[drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe A FIFO underrun
Changing virtual terminals doesn't work. If I ssh into the computer, it all seems calm, it all works, and when I run `journalctl -xe', I can read clearly the same kernel message above.
I have tested both the default kernel, and the `linux-lts' kernel, and I can reproduce the above in both of them (both always boot in UEFI mode, with Intel Microcode properly loaded). Both the cpu and the graphics card are Intel. Here's some info:
[smt-dell ~]$ uname -a
Linux smt-dell 4.0.4-2-ARCH #1 SMP PREEMPT Fri May 22 03:05:23 UTC 2015 x86_64 GNU/Linux
[smt-dell ~]$ lspci |grep -i vga
00:02.0 VGA compatible controller: Intel Corporation Broadwell-U Integrated Graphics (rev 09)
I have absolutely no idea what this bizarre behaviour could mean, or what package could be acting poorly. Does anyone have the slightest idea?
Thanks
Last edited by fofoni (2015-06-02 09:26:28)

Answer 1

Solved. It was just a matter of following the recommendation that was given when I installed the video driver `xf86-video-intel':
This driver uses SNA as the default acceleration method. You can try
falling back to UXA if you run into trouble. To do so, save a file with
the following content as /etc/X11/xorg.conf.d/20-intel.conf :
Section "Device"
Identifier "Intel Graphics"
Driver "intel"
Option "AccelMethod" "uxa"
#Option "AccelMethod" "sna"
EndSection