How to disable one Radeon output?

[Boszormenyi Zoltan]

Hi,

I have a small Kabini base mini PC that has a primary DisplayPort-0
output and a secondary HDMI-0 output.

I would like to have a configuration where only the primary is used
no matter if there's a monitor attached to the secondary.
(Don't ask, business requirements.)

No matter how I try, the secondary monitor output is the clone
of the primary.

Is there a way to disable a specific Radeon output from xorg.conf?

Here's a configuration below that should work but doesn't.

The same method works for the Intel driver: explicitly reference
the to-be-disabled ZaphodHead in a Device section, a Screen section
in turn references this Device section and then leaving the second
Screen out of the ServerLayout section give the desired result,
X leaves the unwanted output in terminal mode.

Section "Monitor"
     Identifier    "HDMI-0"
     Option        "AutoServerLayout" "on"
EndSection

Section "Monitor"
     Identifier    "DisplayPort-0"
     Option        "AutoServerLayout" "on"
EndSection

Section "Device"
     Identifier    "RADEON"
     Driver        "radeon"
     BusID        "PCI:0:1:0"
     Option        "AutoServerLayout" "on"
     Option        "ZaphodHeads" "DisplayPort-0"
     Option        "Monitor-DisplayPort-0" "DisplayPort-0"
     Option        "TearFree" "on"
     Option          "DRI"    "3"
EndSection

Section "Device"
     Identifier    "RADEON1"
     Driver        "radeon"
     BusID        "PCI:0:1:0"
     Option        "AutoServerLayout" "on"
     Option        "ZaphodHeads" "HDMI-0"
     Option        "Monitor-HDMI-0" "HDMI-0"
     Option        "TearFree" "on"
     Option          "DRI"    "3"
EndSection

Section "Screen"
     Identifier    "SCREEN"
     Option        "AutoServerLayout" "on"
     Device        "RADEON"
     Monitor        "Monitor-DisplayPort-0"
EndSection

Section "Screen"
     Identifier    "SCREEN1"
     Option        "AutoServerLayout" "on"
     Device        "RADEON1"
     Monitor        "Monitor-HDMI-0"
EndSection

Section "ServerLayout"
     Identifier    "LAYOUT"
     Option        "AutoServerLayout" "on"
     Screen 0 "SCREEN"
EndSection

Thanks in advance,
Zoltán Böszörményi