Bug 16927

Summary: xorg.conf's PreferredMode overridden by RandR when starting up X
Product: xorg Reporter: Alec Habig <ahabig>
Component: Server/DDX/XorgAssignee: Xorg Project Team <xorg-team>
Status: RESOLVED MOVED QA Contact: Xorg Project Team <xorg-team>
Severity: normal    
Priority: high CC: ahabig, arequipeno, mrmazda
Version: git   
Hardware: Other   
OS: All   
Whiteboard: 2011BRB_Reviewed
i915 platform: i915 features:
Attachments:
Description Flags
Xorg.0.log none

Description Alec Habig 2008-07-31 12:29:21 UTC 
(This bug grew out of some radeonhd debugging over in bug #16740.  The driver bug is now fixed, so this bug has been opened to discuss the resulting RandR problem).

The RandR machinery has come a long way at being able to guess appropriate defaults without guidance from xorg.conf.  However, it seems to have gone a bit too far, in that it overrides the PreferredModes in the conf file upon startup.

My setup:  a 1920x1200 external LCD on DVI-D_1, and a 1400x1050 laptop LCD on PANEL, RightOf the external monitor.

By default, RandR wants to bring up both monitors in the same resolution, with the larger monitor running in the lower resolution.  If I use RROutputOrder to set the external monitor as the primary one, then the big monitor is ok but PANEL runs in a painful 1920x1200scaled mode.

My own preference is to let each monitor run in their native modes, and the bit of lost virtual screen real estate off the bottom of the smaller monitor is the price I pay for crisp pixels and no headache at the end of the workday.  So, I set:

  (II) RADEONHD(0): Output DVI-D_1 using monitor section DoubleSightDVI
  (**) RADEONHD(0): Option "PreferredMode" "1920x1200"
  (II) RADEONHD(0): Output VGA_1 has no monitor section
  (II) RADEONHD(0): Output PANEL using monitor section ThinkpadLCD
  (**) RADEONHD(0): Option "PreferredMode" "1400x1050"
  (**) RADEONHD(0): Option "RightOf" "DoubleSightDVI"

RandR decides that no, you really want to be running the same resolutions, silly boy!  and proceeds to lie:

  (II) RADEONHD(0): Using user preference for initial modes

then set:

  (II) RADEONHD(0): Output DVI-D_1 using initial mode 1920x1200
  (II) RADEONHD(0): Output PANEL using initial mode 1920x1200Scaled

Now, I can then proceed to manually set things right:

  xrandr --output PANEL --mode 1400x1050

and things work fine.  The Bug (IMHO) is that RandR isn't honoring the xorg.conf file set PreferredModes.  It recognizes that I set them with the "+" label in its list, but decides to Do Its Own Thing anyway.  One shouldn't have to shell script something which there's already conf file option for.

(System: up to date Fedora 9 system, xorg-x11-server-utils-7.4-1.fc9.i386, xorg-x11-radeonhd from git head.  See bug #16740 for a plethora of logging).
Comment 1 Alec Habig 2008-08-14 09:07:38 UTC 
The choice to automatically scale the secondary monitor to exactly match the primary one is even sillier in the case of the new monitor I just tried.  At 1680x1050, the Y axes already match, so a LeftOf or RightOf setup (with the PANEL in native 1400x1050) is perfect.  Yet the default is for PANEL to come up in 1680x1050scaled, ignoring the xorg.conf set PreferredModes. 

xrandr from the command line happily puts the PANEL back in its native mode.  Any ideas at all on how to make PreferredMode be honored?
Comment 2 Ian Pilcher 2009-02-26 08:46:24 UTC 
I'm seeing something similar.  (See bug #20310.)  In my case it's running my
1280x1024 LCD at 1400x1050.

Not to be too whiny, but running a display at a resolution which it doesn't
support seems like an obvious bug, one which merits at least some response.

Thanks!
Comment 3 Aaron Plattner 2013-02-06 18:20:27 UTC 
Moving to the DDX (I'm assuming radeonhd uses the common server infrastructure for this).

The mode selection code changed a while back, IIRC.  Is this still a problem?
Comment 4 Felix Miata 2013-06-27 03:51:27 UTC 
Created attachment 81520 [details]
Xorg.0.log

(In reply to comment #3)
> The mode selection code changed a while back, IIRC.  Is this still a problem?

I believe so. Using an rv380 with VGA-0 default and DVI-0 & S-video secondaries, PreferredMode is not obeyed if the only cable is connected to DVI-0, and the configfile does not explicitly direct its applicability to DVI-0.
Comment 5 GitLab Migration User 2018-12-13 18:28:17 UTC 
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