xrandr output on my system when the problem is in place:

$ xrandr                                                    
Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 8192 x 8192
eDP-1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 344mm x 193mm
   1920x1080     60.00 +  59.97*   59.96    59.93  
   1680x1050     59.95    59.88  
   1600x1024     60.17  
   1400x1050     59.98  
   1600x900      59.99    59.94    59.95    59.82  
   1280x1024     60.02  
   1440x900      59.89  
   1400x900      59.96    59.88  
   1280x960      60.00  
   1440x810      60.00    59.97  
   1368x768      59.88    59.85  
   1360x768      59.80    59.96  
   1280x800      59.99    59.97    59.81    59.91  
   1152x864      60.00  
   1280x720      60.00    59.99    59.86    59.74  
   1024x768      60.04    60.00  
   960x720       60.00  
   928x696       60.05  
   896x672       60.01  
   1024x576      59.95    59.96    59.90    59.82  
   960x600       59.93    60.00  
   960x540       59.96    59.99    59.63    59.82  
   800x600       60.00    60.32    56.25  
   840x525       60.01    59.88  
   864x486       59.92    59.57  
   800x512       60.17  
   700x525       59.98  
   800x450       59.95    59.82  
   640x512       60.02  
   720x450       59.89  
   700x450       59.96    59.88  
   640x480       60.00    59.94  
   720x405       59.51    58.99  
   684x384       59.88    59.85  
   680x384       59.80    59.96  
   640x400       59.88    59.98  
   576x432       60.06  
   640x360       59.86    59.83    59.84    59.32  
   512x384       60.00  
   512x288       60.00    59.92  
   480x270       59.63    59.82  
   400x300       60.32    56.34  
   432x243       59.92    59.57  
   320x240       60.05  
   360x202       59.51    59.13  
   320x180       59.84    59.32  
VGA-1 disconnected (normal left inverted right x axis y axis)
DP-1 disconnected (normal left inverted right x axis y axis)
HDMI-1 disconnected (normal left inverted right x axis y axis)
DP-2 disconnected (normal left inverted right x axis y axis)
HDMI-2 disconnected (normal left inverted right x axis y axis)
DP-2-1 connected (normal left inverted right x axis y axis)
   1920x1080     60.00 +  50.00    59.94  
   1680x1050     59.88  
   1400x1050     59.95  
   1600x900      60.00  
   1280x1024     75.02    60.02  
   1440x900      59.90  
   1280x960      60.00  
   1280x800      59.91  
   1152x864      75.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.03    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  
DP-2-2 connected (normal left inverted right x axis y axis)
   1920x1080     60.00 +  50.00    59.94  
   1680x1050     59.88  
   1400x1050     59.95  
   1600x900      60.00  
   1280x1024     75.02    60.02  
   1440x900      59.90  
   1280x960      60.00  
   1280x800      59.91  
   1152x864      75.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.03    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  
DP-2-3 disconnected (normal left inverted right x axis y axis)


When trying to activate one of the external displays I get this:

$ xrandr --output DP-2-2  --auto --right-of eDP-1  --verbose
screen 0: 3840x1080 1013x285 mm  96.25dpi
crtc 1:    1920x1080  60.00 +1920+0 "DP-2-2"
xrandr: Configure crtc 1 failed
crtc 0: disable
crtc 1: disable
crtc 2: disable
screen 0: revert
crtc 0: revert
crtc 1: revert
crtc 2: revert

Rebooting the system fixes the issue but it re-occurs from time to time on different kernel versions.

Hi Evgheni - How often does this issue reproduce?

Also, please try to reproduce the error using drm-tip (https://cgit.freedesktop.org/drm-tip) and kernel parameters drm.debug=0x1e log_buf_len=4M, and if the problem persists attach the full dmesg from boot.

Hi James, thanks for the fast reply.

I can't reliably reproduce it - pops up once in a couple of weeks (the system is always turned on). I've enabled debugging and will wait for the problem to re-occur, will share the logs here once that happens.

Created attachment 141397 [details]
dmesg outout around issue

I've not been able to catch the issue for some time and as I was constantly running out of disk space due to debug logs I decided to undock to see if that's related.

Attaching dmesg output around the period: the laptop was undocked at 712379 and docked at 712384. The fifo underrun error appeared immediately after that and both external displays stopped working. There was no kernel backtrace this time.

Software versions used are:
kernel 4.17.0-3-amd64 (Debian)
libdrm-intel1-2.4.93-1
xserver-xorg-video-intel 2.99.917+git20171229-1+b1

> Attaching dmesg output around the period: the laptop was undocked at 712379
> and docked at 712384. The fifo underrun error appeared immediately after
> that and both external displays stopped working. There was no kernel
> backtrace this time.

Were you able to update drm-tip to latest? is this logs from latest drm-tip?
https://cgit.freedesktop.org/drm-tip

Evgheni, ping?

Unfortunately I didn't have time to build a kernel and try drm-tip on it. The logs provided are from kernel 4.17.17 as shipped with Debian Unstable.

Evgheni, do you still have the issue with latest kernel?

I did a few tests and did not see this issue on kernel 4.18.10 and libdrm-intel1 2.4.94 so we can probably close this

Thanks for the feedback. Closing this bug.