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When I enter: man radeon I get the output:

Option "ReverseDDC" "boolean" When BIOS connector informations aren't available, use this option to reverse the mapping of the 2 main DDC ports. Use this if the X server obviously detects the wrong display for each connector. This is typically needed on the Radeon 9600 cards bundled with Apple G5s. The default is off.

Every time I boot I am met with a low resolution login screen, which is fine, but when I enter my password to boot into the desktop environment I'm met with a No Signal message on the screen and I have to physically switch the connector port. Does anyone know what to do, or how to fix this?

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up vote 2 down vote accepted

When I installed Ubuntu 10.10 (or any distro derived from debian) I had a similar problem. I managed to fix it by additing the below line to the Section "Device"and naming the Driver "radeon";

Option "Reverse DDC" "on" 

For eg my xorg.conf file would have looked something like;

    Section "ServerLayout"
Identifier "X.org Configured"
Screen 0 "Screen0" 0 0
InputDevice "Mouse0" "CorePointer"
InputDevice "Keyboard0" "CoreKeyboard"
EndSection

Section "Files"
ModulePath "/usr/lib/xorg/modules"
FontPath "/usr/share/fonts/X11/misc"
FontPath "/usr/share/fonts/X11/cyrillic"
FontPath "/usr/share/fonts/X11/100dpi/:unscaled"
FontPath "/usr/share/fonts/X11/75dpi/:unscaled"
FontPath "/usr/share/fonts/X11/Type1"
FontPath "/usr/share/fonts/X11/100dpi"
FontPath "/usr/share/fonts/X11/75dpi"
FontPath "/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType"
FontPath "built-ins"
EndSection

Section "Module"
Load "record"
Load "glx"
Load "dbe"
Load "dri2"
Load "extmod"
Load "dri"
EndSection

Section "InputDevice"
Identifier "Keyboard0"
Driver "kbd"
EndSection

Section "InputDevice"
Identifier "Mouse0"
Driver "mouse"
Option "Protocol" "auto"
Option "Device" "/dev/input/mice"
Option "ZAxisMapping" "4 5 6 7"
EndSection

Section "Monitor"
Identifier "Monitor0"
VendorName "Monitor Vendor"
ModelName "Monitor Model"
EndSection

Section "Device"
Driver "radeon"
### Values: <i>: integer, <f>: float, <bool>: "True"/"False",
### <string>: "String", <freq>: "<f> Hz/kHz/MHz",
### <percent>: "<f>%"
### [arg]: arg optional
#Option "NoAccel" # [<bool>]
#Option "SWcursor" # [<bool>]
#Option "Dac6Bit" # [<bool>]
#Option "Dac8Bit" # [<bool>]
#Option "BusType" # [<str>]
#Option "CPPIOMode" # [<bool>]
#Option "CPusecTimeout" # <i>
#Option "AGPMode" # <i>
#Option "AGPFastWrite" # [<bool>]
#Option "AGPSize" # <i>
#Option "GARTSize" # <i>
#Option "RingSize" # <i>
#Option "BufferSize" # <i>
#Option "EnableDepthMoves" # [<bool>]
#Option "EnablePageFlip" # [<bool>]
#Option "NoBackBuffer" # [<bool>]
#Option "DMAForXv" # [<bool>]
#Option "FBTexPercent" # <i>
#Option "DepthBits" # <i>
#Option "PCIAPERSize" # <i>
#Option "AccelDFS" # [<bool>]
#Option "IgnoreEDID" # [<bool>]
#Option "CustomEDID" # [<str>]
#Option "DisplayPriority" # [<str>]
#Option "PanelSize" # [<str>]
#Option "ForceMinDotClock" # <freq>
#Option "ColorTiling" # [<bool>]
#Option "VideoKey" # <i>
#Option "RageTheatreCrystal" # <i>
#Option "RageTheatreTunerPort" # <i>
#Option "RageTheatreCompositePort" # <i>
#Option "RageTheatreSVideoPort" # <i>
#Option "TunerType" # <i>
#Option "RageTheatreMicrocPath" # <str>
#Option "RageTheatreMicrocType" # <str>
#Option "ScalerWidth" # <i>
#Option "RenderAccel" # [<bool>]
#Option "SubPixelOrder" # [<str>]
#Option "ClockGating" # [<bool>]
#Option "VGAAccess" # [<bool>]
#Option "ReverseDDC" # [<bool>]
#Option "LVDSProbePLL" # [<bool>]
#Option "AccelMethod" # <str>
#Option "DRI" # [<bool>]
#Option "ConnectorTable" # <str>
#Option "DefaultConnectorTable" # [<bool>]
#Option "DefaultTMDSPLL" # [<bool>]
#Option "MacModel" # <str>
#Option "TVDACLoadDetect" # [<bool>]
#Option "ForceTVOut" # [<bool>]
#Option "TVStandard" # <str>
#Option "IgnoreLidStatus" # [<bool>]
#Option "DefaultTVDACAdj" # [<bool>]
#Option "Int10" # [<bool>]
#Option "EXAVSync" # [<bool>]
#Option "ATOMTVOut" # [<bool>]
#Option "R4xxATOM" # [<bool>]
#Option "ForceLowPowerMode" # [<bool>]
#Option "DynamicPM" # [<bool>]
#Option "NewPLL" # [<bool>]
#Option "ZaphodHeads" # <str>
Option "Reverse DDC" "on"
Identifier "Card0"
Driver "radeon"
BusID "PCI:240:16:0"
EndSection

Section "Screen"
Identifier "Screen0"
Device "Card0"
Monitor "Monitor0"
SubSection "Display"
Viewport 0 0
Depth 1
EndSubSection
SubSection "Display"
Viewport 0 0
Depth 4
EndSubSection
SubSection "Display"
Viewport 0 0
Depth 8
EndSubSection
SubSection "Display"
Viewport 0 0
Depth 15
EndSubSection
SubSection "Display"
Viewport 0 0
Depth 16
EndSubSection
SubSection "Display"
Viewport 0 0
Depth 24
EndSubSection
EndSection

If you don't have an xorg file (as newer versions of ubuntu do not generally come with one) one can be created by running;

Xorg -configure

This seems to have done the trick with all debian based distros that I have since installed on my G5. You can see more details on the link below;

http://manpages.ubuntu.com/manpages/precise/man4/radeon.4.html

I hope that helps.

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Awesome answer man! Thanks! –  etsr Feb 22 '13 at 1:37
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