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Using fglrx and trying to set up dual-monitor setup here. Here's what xrandr says:

Screen 0: minimum 320 x 200, current 1400 x 1050, maximum 1600 x 1600

So, you know this one already, right? All I have to do is adjust Virtual screen size in xorg.conf. But I have, here's the whole file:

Section "ServerLayout"
    Identifier     "aticonfig Layout"
    Screen      0  "virtual screen" 0 0
EndSection

Section "Monitor"
    Identifier   "Monitor."
    Option      "DPMS" "true"
EndSection

Section "Device"
    Identifier  "hd6450"
    Driver      "fglrx"
    BusID       "PCI:1:0:0"
    Option      "mtrr"          "no"
    Option      "no_dri"        "no"
    Option      "no_accel"      "no"
EndSection

Section "Screen"
    Identifier "virtual screen"
    Device     "hd6450"
    SubSection "Display"
        Virtual   3600 1080
    EndSubSection
EndSection

Judging from Xorg.0.log, the resolution is silently dropped to 1600x1600 which is not enough. If I set the Virtual size to 2048 2048 I can get my monitors at native resolution of 1680x1050 but I cannot use the second monitor:

~ % xrandr --output CRT1 --left-of DFP2
xrandr: screen cannot be larger than 2048x2048 (desired size 3360x1050)

So what to do? I've tried fglrx versions 11.11 and 11.8. Oddly enough, amdcccle doesn't let me edit any of the settings. The inputs are all disabled from editing. Thanks for your attention.

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2 Answers 2

up vote 2 down vote accepted

Could you add card model? I just tested on my test machine, and it surely accepted:

    Virtual   4096 4096

Can you add the output of 'xrandr'? Here's mine (HD5850, 09:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI Cypress LE [Radeon HD 5800 Series])

Screen 0: minimum 320 x 200, current 2048 x 1152, maximum 4096 x 4096
DFP1 disconnected (normal left inverted right x axis y axis)
DFP2 disconnected (normal left inverted right x axis y axis)
DFP3 disconnected (normal left inverted right x axis y axis)
DFP4 connected 2048x1152+0+0 (normal left inverted right x axis y axis) 510mm x 287mm
   2048x1152      59.9*+
   1920x1080      59.9  
   1680x1050      60.0  
   1400x1050      60.0  
   1600x900       60.0  
   1360x1024      60.0  
   1280x1024      60.0  
   1440x900       59.9  
   1280x960       60.0  
   1280x800       59.8  
   1280x768       59.8  
   1280x720       59.8  
   1024x768       60.0  
   800x600        60.3     56.2  
   640x480        59.9  
CRT1 disconnected (normal left inverted right x axis y axis)
CRT2 disconnected (normal left inverted right x axis y axis)

See comment.

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1  
That's it. The ratio between WIDTH and HEIGHT apparently has to be within some limit. 1:1 is always okay. :) I wondered why I had a well working Virtual size of '3060 1680' about a year ago (last time I had ATI) but now I can't set up 3360 1080. –  progo Mar 1 '12 at 21:31

Not every number can be used for the "Virtual" directive in case of fglrx. Not sure what the exact policy is, but "3600 1080" will not work. Try "3600 1200". If doesn't work, try "3600 3600" then "3600 1800" too. Don't worry about the numbers too much, xrandr will actually use a smaller area, but for some reason the driver expects "round" numbers.

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Thanks. We solved the problem in @qdot's answer. See the comment :) –  progo Mar 23 '12 at 14:43

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