Hello. I'm running Devuan Chimaera on a Dell Optiplex 3020, and today I installed an AMD Radeon HD 8490 video card with one DVI output and one DisplayPort output. Here is the output of lspci | grep VGA (the first line describes the built-in graphics controller which is not currently in use, and the second line is the controller to which I have attached two displays):

00:02.0 VGA compatible controller: Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor Integrated Graphics Controller (rev 06)
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Caicos XTX [Radeon HD 8490 / R5 235X OE

I have xserver-xorg-video-radeon (version 1:19.1.0-2) installed, and the output of find /sys | grep drivers.*01:00.0 is /sys/bus/pci/drivers/radeon/0000:01:00.0.

Here is the problem: for some reason the 1280x1024 DVI display on the right is showing, at its left edge, a copy of the right-most two columns of pixels from the 1366x768 DP display on the left; and the image that should be shown starting at the left edge of the right display (including wallpaper) instead begins in column three (which also means that the last two columns at the right side of the right display are off the edge of the screen and not shown). Windows on the right display snap to the third column of pixels instead of the first, and there is a two-pixel-wide "hump" at the bottom of the left edge of the right display around which the mouse pointer must pass to reach the left display (since the displays are aligned at their top edges and the left display is shorter than the right). I did some experimenting with the contents of ~/.config/monitors.xml but was unable to completely resolve the problem (I could subtract 2 from the X positions of both displays and get the border between the displays to end up in the right spot, but then the left-hand display's effective left edge, set at -2, somehow moved to the right, uncovering two columns of pixels of unknown origin). The problem doesn't seem to be exclusive to MATE, as logging out takes me to the login screen where the wallpaper on the monitors aligns in the same unexpected way as when logged into MATE.

The problem is the same as what's discussed on the following page, which also has a very helpful illustration: https://unix.stackexchange.com/question … ternal-dis

The output of xrandr is shown below:

Screen 0: minimum 320 x 200, current 2646 x 1024, maximum 16384 x 16384
DisplayPort-1 connected 1366x768+0+0 (normal left inverted right x axis y axis) 410mm x 230mm
   1366x768      59.79*+
   1280x1024     75.02  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   640x480       75.00    59.94  
   720x400       70.08  
DVI-0 connected primary 1280x1024+1366+0 (normal left inverted right x axis y axis) 338mm x 270mm
   1280x1024     60.02*+
   1280x960      60.00  
   1152x864      75.00  
   1024x768      75.03    70.07    60.00  
   832x624       74.55  
   800x600       72.19    75.00    60.32    56.25  
   640x480       75.00    72.81    66.67    59.94  
   720x400       70.08  

Thank you for your assistance, and please let me know if there is additional information I can provide that would be useful.