RandR: multi-referenced monitor sections & problems with them

Matthias Hopf mhopf at suse.de
Thu Mar 13 10:55:44 PDT 2008

I just stumbled over some strange behavior, and it definitely changed
past Xserver 1.4.0 (don't know the exact version yet, bisecting this
would be probably worth it).

A snippet of the config I'm testing is

Section "Monitor"
  Identifier "M1"
Section "Monitor"
  Identifier "M2"
  Option     "Right-Of" "M1"

Section "Device"
  Identifier "D"
  Driver "radeonhd"
  Option "monitor-DVI-I_1/digital" "M1"
  Option "monitor-DVI-I_2/digital" "M2"

Section "Screen"
  Identifier "S"
  Device "D"
  Monitor "M1"


So basically a static multi-monitor setup for RandR 1.2, with one of the
monitors additionally referenced in the Screen section. This monitor
reference shouldn't be used at all, because the driver sets
use_screen_monitor to FALSE for all outputs.

This used to work - however, beginning with 1.4.90 the multi-monitor
setup fails if and only if I use the two digital DVI outputs on this
card, with DVI and VGA it works fine, with DVI/d and DVI/a it also works
fine. If I remove the reference to the M1 monitor in the Screen section
it works fine. If I add another monitor and reference it in the Screen
section instead it works fine. It's probably difficult to reproduce this
with another driver, but this shouldn't be a driver issue.

Does anybody have a clue WTF is going on here, is this considered
standard behavior or rather a bug? If it's standard, why is its behavior
depending on the outputs (and not on the monitors)?



Matthias Hopf <mhopf at suse.de>      __        __   __
Maxfeldstr. 5 / 90409 Nuernberg   (_   | |  (_   |__          mat at mshopf.de
Phone +49-911-74053-715           __)  |_|  __)  |__  R & D   www.mshopf.de

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