Linux 3.x: Flickering when logging into GNOME Shell or Unity

[Alex Deucher]

On Wed, Oct 17, 2012 at 4:48 PM, Paul Menzel
<paulepanter at users.sourceforge.net> wrote:
> Am Mittwoch, den 17.10.2012, 16:25 -0400 schrieb Alex Deucher:
>> On Wed, Oct 17, 2012 at 11:26 AM, Paul Menzel wrote:
>
>> > Am Mittwoch, den 17.10.2012, 16:49 +0200 schrieb Paul Menzel:
>> >
>> >> setting up an ASUS M2A-VM after some months with
>> >>
>> >>         [    3.178337] [drm] initializing kernel modesetting (RS690 0x1002:0x791E 0x1043:0x826D).
>> >>
>> >> logging in into GNOME Shell (GNOME 3) or for testing with Ubuntu 12.04
>> >> and Unity, the image flickers for a second and then works normally.
>> >>
>> >> Turning on debugging
>> >>
>> >>         /sys/module/drm/parameters$ echo "0x06" | sudo tee debug
>> >>         sudo: unable to resolve host granit
>> >>         0x06
>> >>
>> >> before logging in, the following is logged. Looking at the source code,
>> >> I do not see that this is supposed to be a problem. But maybe you can
>> >> figure out more.
>> >>
>> >>         [  454.896408] [drm:drm_mode_addfb], [FB:41]
>> >>         [  454.896427] [drm:radeon_crtc_page_flip], flip-ioctl() cur_fbo = ffff880072438400, cur_bbo = ffff880037072400
>> >
>> > trying Linux 3.5
>> >
>> >         $ dpkg -l linux-image-3.5* | grep ii | tr -s ' ' | cut -d ' ' -f 2-4
>> >         linux-image-3.5-trunk-amd64 3.5.5-1~experimental.1 amd64
>> >
>> > the flickering is still there.
>>
>> I don't see anything wrong in the log.  Does the flicker occur at
>> regular intervals or just at start up?
>
> As far as I see, one second after hitting enter in the graphical login
> manager (LightDM in this case).
>
>> I suspect the flicker may be due to your desktop environment probing
>> for monitors at startup
>
> Hmm. Only a VGA monitor is detected and I do not see that issue on
> different system where I tested GNOME Shell to reproduce this. I have
> test Unity too again.
>

Depends on the system and what connectors they have and whether or not
they support load detection.

> Though the probing should be in the logs somehow? But there are not
> during the time of login.
>
>> which causes a flicker if nothing is attached to the analog ports
>> (VGA, s-video) as that results in a load detection operation to probe
>> for old monitors without EDIDs or analog TVs.
>
> Any hint on how to rule that out? Disable some outputs on the command
> line or so?

Depending on what is doing the probing you could try starting bare X
without a desktop environment.  Or disable the analog outputs you
aren't using in your xorg.conf.  E.g.,

  Section "Monitor"
    Identifier "S-video"
    Option "Disable" "true"
  EndSection


Alex