xrandr does not find modes defined in xorg.conf

Marius Gedminas marius at pov.lt
Wed Jan 3 10:17:54 UTC 2007


On Wed, Jan 03, 2007 at 11:02:11AM +0100, Nils wrote:
> I have a strange problem on a T43p Laptop with Edgy on it.

T43p has an ATI Radeon video card.  I assume you use the default,
open-source 'radeon' driver for it.

> When I
> execute xrandr --query, it only shows the current resolution, but not
> these in xorg.conf. I'm not sure where xrandr gets the resultions
> from, but I don't think it's xorg.conf.

You appear to have the MergedFB option enabled (I think it's enabled by
default).  In that case xrandr takes the list of modes from the
MetaModes option in xorg.conf.  If there's no such option, it will know
about only one mode (the biggest one).  The radeon(4) manual page will
tell you more.

> Another problem i have is that i cannot change the resolutions with
> ctrl-alt-+/-. I'm not sure if KDE is blocking or if it's a problem if
> the +/- is not on a numeric keypad (since it's a laptop..).

Same reason as above.  Both xrandr and Ctrl-Alt-+/- use the mode
combinations from MetaModes, when MergedFB is enabled.

> Thanks for comments and suggestions.

If you do not intend to use an external monitor (or projector), disabling
MergedFB seems to be the simplest option.  Add

    Option          "MergedFB"      "false"

to the Device section in your xorg.conf.

If you do intend to use an external monitor, add MetaModes instead, e.g.

    Option          "MetaModes"     "1024x768 800x600 640x480"

will let you switch between three different clone modes (same picture on
both monitors), while

    Option          "MetaModes"     "1024x768-1024x768 1024x768 800x600 640x480"

will also let you use one extended desktop mode.

People are now working on improving the randr extension.  In the future
you should be able to switch video modes without having to manual pages
and craft custom xorg.conf files.  This feature is unlikely to make it
into Feisty, but I hope to see it in the next release after Feisty.


Warning: in Edgy there appears to be a bug in the X server that makes
xrandr stop working sometimes.  By "stop working" I mean that you can
request mode changes, but they do not take effect, and no error message
is shown.  Restarting the X server solves the problem, but requires you
to close all running programs, which is often inconvenient.

Still, it's better than the bug in Dapper where the radeon driver would
randomly crash your system.

Marius Gedminas
-- 
This sentence contradicts itself -- no actually it doesn't.
                -- Douglas Hofstadter
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