[Bug 109680] Multiple cards with modesetting results in Segmentation Fault

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=109680

--- Comment #5 from ToBeReplaced at gmail.com ---
Thank you for all of the help. I have come to a resolution based on your hunch
about removing Screen lines in the device sections.

The segmentation fault appears to occur if there is no "Screen 0" for a given
BusID. The core misunderstanding was that the screen number in the ServerLayout
section is *not* related to the screen number in the Device section.

My comment about ZaphodHeads was because I originally had a third screen based
off of the second bus id, but I removed it from the configuration since it was
not required to cause a Segmentation Fault. My end goal was display :0.0 on one
card, :0.1 on another card, and :0.2 on that second card.

A working configuration, with comments for the "surprises" I had is below, in
case it is useful for anyone in the future or for improving existing
documentaiton.

Section "ServerLayout" 
    Identifier "Example" 
    Screen 0 "A" 
    Screen 1 "B" 
    Screen 2 "C" 
EndSection 

Section "Device" 
    Identifier "A Card" 
    Driver "modesetting" 
    Screen 0 
    BusID "PCI:16 at 0:0:0" 
    Option "kmsdev" "/dev/dri/card1"
    Option "Monitor-DVI-D-1" 
EndSection 

Section "Monitor" 
    Identifier "A Monitor" 
EndSection 

Section "Screen" 
    Identifier "A" 
    Device "A Card" 
    Monitor "A Monitor" 
EndSection 

Section "Device" 
    Identifier "B Card" 
    Driver "modesetting" 
    Screen 0 # 1st screen for bus, 2nd screen in layout
    BusID "PCI:56 at 0:0:0" 
    Option "kmsdev" "/dev/dri/card0"
    Option "Monitor-HDMI-1" 
EndSection 

Section "Monitor" 
    Identifier "B Monitor" 
EndSection 

Section "Screen" 
    Identifier "B" 
    Device "B Card" 
    Monitor "B Monitor" 
EndSection 

Section "Device"
    Identifier "C Card"
    Driver "modesetting"
    Screen 1 # 2nd screen for bus, 3rd screen in layout
    BusID "PCI:56 at 0:0:0"
    Option "kmsdev" "/dev/dri/card0"
    Option "Monitor-HDMI-2"
    Option "ZaphodHeads" "HDMI-2"
EndSection

Section "Monitor"
    Identifier "C Monitor"
EndSection

Section "Screen"
    Identifier "C"
    Device "C Card"
    Monitor "C Monitor"
EndSection

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