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I'm using latest ArchLinux with dual monitor, but my second monitor is not detected

$ lspci | grep VGA
00:01.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Richland [Radeon HD 8570D]

$ pacman -Q | grep xorg-server
xorg-server 1.15.1-1
xorg-server-common 1.15.1-1
xorg-server-utils 7.6-3

$ pacman -Q | grep catalyst
catalyst-hook 14.4-10
catalyst-libgl 14.4-11
catalyst-utils 14.4-10
lib32-catalyst-utils 14.4-11
lib32-opencl-catalyst 14.4-10
opencl-catalyst 14.4-10

$ cat /etc/X11/xorg.conf
Section "ServerLayout"
        Identifier     "aticonfig Layout"
        Screen      0  "aticonfig-Screen[0]-0" 0 0

Section "Module"

Section "Monitor"
        Identifier   "aticonfig-Monitor[0]-0"
        Option      "VendorName" "ATI Proprietary Driver"
        Option      "ModelName" "Generic Autodetecting Monitor"
        Option      "DPMS" "true"

Section "Device"
        Identifier  "aticonfig-Device[0]-0"
        Driver      "fglrx"
        BusID       "PCI:0@0:1:0"

Section "Screen"
        Identifier "aticonfig-Screen[0]-0"
        Device     "aticonfig-Device[0]-0"
        Monitor    "aticonfig-Monitor[0]-0"
        DefaultDepth     24
        SubSection "Display"
                Viewport   0 0
                Depth     24
                Modes    "1280x1024"

$ xrandr -q
Screen 0: minimum 320 x 200, current 1600 x 900, maximum 16384 x 16384
DFP1 disconnected (normal left inverted right x axis y axis)
CRT1 connected 1600x900+0+0 (normal left inverted right x axis y axis) 434mm x 236mm
   1280x1024     75.02 +  60.02  
   1600x900      60.00*+
   1440x900      60.00  
   1280x960      75.02    60.02  
   1280x768      75.02    60.02  
   1280x720      60.00  
   1024x768      75.03    70.07    60.00  
   1024x600      75.03    70.07    60.00  
   800x600       72.19    75.00    60.32    56.25  
   800x480       72.19    75.00    60.32    56.25  
   640x480       75.00    72.81    67.00    59.94  

$ xrandr --output CRT1 --mode 1600x900 --output DFP1 --mode 1366x768 --right-of CRT1
xrandr: cannot find mode 1366x768

The question:

  1. How to fill xorg.conf when I don't know which BusID to put (I'm using onboard graphic card), the current display are the VGA/D-Sub port, the other one is DVI-D/24+1 port --> the one that new monitor plugged in
  2. What should I really put when I need horizontal span on my first monitor AOC E2070SWNL (1600x900) and the second new monitor Acer P166HQL (1366x768)?
share|improve this question
nevermind this post, the problem was on the passive DVI-D (24+1) to D-Sub/VGA converter – drerayo May 1 '14 at 14:58
Do you mean that your problem was faulty hardware? Or was it a problem with your software configuration, and if so, how did you solve it? – Gilles May 1 '14 at 17:43
yes, faulty hardware, I need active DVI-D to D-Sub converter, since I don't have it yet, I can't solve this problem for now.. – drerayo May 2 '14 at 4:01

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