I'm having a great deal of difficulty making the latest Catalyst/fglrx drivers usable on my Ubuntu Natty 11.4 dual-head workstation. I've tried it with the Ubuntu-packaged drivers, r8.840, and by following the directions to build fglrx from the latest drivers, r.8.850. In both cases I was able to get Xorg/KDE to run, using aticonfig and a little hand-tweaking as necessary. However, no matter what I did, my 2nd monitor would have terrible flickering, making it very difficult to use. With a single monitor in place, no issues. With the OSS radeon drivers, no problem. With the old nVidia 8400GS card that I used to use, no problem (just slow!) I just can't get the Catalyst drivers to drive two monitors in a stable, non-headache-inducing way.

This sounds a lot like similar issues that Windows users have reported with Cypress cards and dual-head flickering. In their cases, the issue had to do with idle clock rates that were too low to handle two monitors without flicker. However, I can't find anything in the aticonfig settings to adjust idle clocks, only peak clocks.

lspci:
Code:
01:00.0 VGA compatible controller: ATI Technologies Inc Cypress [Radeon HD 5800 Series] (prog-if 00 [VGA controller])
        Subsystem: Giga-byte Technology Device 21e4
        Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR+ FastB2B- DisINTx+
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
Note that I tried this with and without Xinerama, with and without XRandR 1.2 enabled, and with and without the --dtop line. No combination fixed the flicker. Here's a sample of my final attempt before giving up and going back to OSS Radeon drivers.

aticonfig commands, final attempt:
Code:
sudo aticonfig --initial=dual-head --screen-layout=right --xinerama=on
sudo aticonfig --set-pcs-str="DDX,EnableRandR12,FALSE"
sudo aticonfig --dtop=horizontal --overlay-on=1
resulting xorg.conf:
Code:
Section "ServerLayout"
        Identifier     "Layout0"
        Screen      0  "aticonfig-Screen[0]-0" 0 0
        Screen         "aticonfig-Screen[0]-1" RightOf "aticonfig-Screen[0]-0"
EndSection

Section "Module"
EndSection

Section "ServerFlags"
        Option      "Xinerama" "on"
EndSection

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

Section "Monitor"
        Identifier   "aticonfig-Monitor[0]-1"
        Option      "VendorName" "ATI Proprietary Driver"
        Option      "ModelName" "Generic Autodetecting Monitor"
        Option      "DPMS" "true"
EndSection

Section "Device"
        Identifier  "aticonfig-Device[0]-0"
        Driver      "fglrx"
        Option      "UseFastTLS" "0"
        Option      "DesktopSetup" "horizontal"
        Option      "OverlayOnCRTC2" "1"
        BusID       "PCI:1:0:0"
EndSection

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

Section "Screen"
        Identifier "Screen0"
        Device     "radeon0"
        Monitor    "VGA1"
        DefaultDepth     24
        SubSection "Display"
                Viewport   0 0
                Depth     24
                Modes    "1280x1024" "1024x768" "800x600" "640x480"
        EndSubSection
EndSection

Section "Screen"
        Identifier "Screen1"
        Device     "radeon0"
        Monitor    "VGA0"
        DefaultDepth     24
        SubSection "Display"
                Viewport   0 0
                Depth     24
                Modes    "1280x1024" "1024x768" "800x600" "640x480"
        EndSubSection
EndSection

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
        EndSubSection
EndSection

Section "Screen"
        Identifier "aticonfig-Screen[0]-1"
        Device     "aticonfig-Device[0]-1"
        Monitor    "aticonfig-Monitor[0]-1"
        DefaultDepth     24
        SubSection "Display"
                Viewport   0 0
                Depth     24
        EndSubSection
EndSection

Section "Extensions"
        Option      "Composite" "Enable"
EndSection