[Bug 83184] New: Screen flickering at low resolution when monitor is attached via VGA dongle to DVI port

[bugzilla-daemon@freedesktop.org]

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https://bugs.freedesktop.org/show_bug.cgi?id=83184

          Priority: medium
            Bug ID: 83184
          Assignee: dri-devel@lists.freedesktop.org
           Summary: Screen flickering at low resolution when monitor is
                    attached via VGA dongle to DVI port
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: Rainer.Koenig@ts.fujitsu.com
          Hardware: x86-64 (AMD64)
            Status: NEW
           Version: unspecified
         Component: DRM/Radeon
           Product: DRI

Created attachment 105377
  --> https://bugs.freedesktop.org/attachment.cgi?id=105377&action=edit
dmesg output with drm debug information

Encountered a strange problem with Radeon HD 6250 (or HD 6310) on a Fujitsu
D3003-S1x mainboard. Occurs with every tested linux distribution and older and
newer kernels. 

Problem occurs only when a monitor is attached via VGA to the DVI port. If the
monitor is attached via DVI then the problem does not occur.

Problem is that
- Monitor is flickering sporadically 
- Monitor resolution is fixed to 1024x768 instead of higher resolutions that
are possible
- xrandr shows 2 monitors while just one monitor is attached

Tried to debug this with kernel parameter drm.debug=14 (dmesg log is attached)
and found the following messages that would explain the flickering screen.

[    4.098364] [drm:radeon_connector_analog_encoder_conflict_solve] 1:
conflicting encoders switching off DVI-I-1
[    4.098369] [drm:radeon_connector_analog_encoder_conflict_solve] in favor of
VGA-1
[    4.219817] [drm:radeon_connector_analog_encoder_conflict_solve] 1:
conflicting encoders switching off VGA-1
[    4.219830] [drm:radeon_connector_analog_encoder_conflict_solve] in favor of
DVI-I-1
[    4.231344] [drm:radeon_connector_analog_encoder_conflict_solve] 1:
conflicting encoders switching off DVI-I-1
[    4.231350] [drm:radeon_connector_analog_encoder_conflict_solve] in favor of
VGA-1
[   13.949336] [drm:radeon_connector_analog_encoder_conflict_solve] 1:
conflicting encoders switching off VGA-1
[   13.949350] [drm:radeon_connector_analog_encoder_conflict_solve] in favor of
DVI-I-1
[   13.967886] [drm:radeon_connector_analog_encoder_conflict_solve] 1:
conflicting encoders switching off DVI-I-1
[   13.967891] [drm:radeon_connector_analog_encoder_conflict_solve] in favor of
VGA-1
[   14.023332] [drm:radeon_connector_analog_encoder_conflict_solve] 1:
conflicting encoders switching off VGA-1
[   14.023345] [drm:radeon_connector_analog_encoder_conflict_solve] in favor of
DVI-I-1
[   14.056688] [drm:radeon_connector_analog_encoder_conflict_solve] 1:
conflicting encoders switching off DVI-I-1
[   14.056694] [drm:radeon_connector_analog_encoder_conflict_solve] in favor of
VGA-1

The problem is still to find the root cause that leads to the issue of having
"conflicting encoders". Any idea what could cause this behaviour?

Regards
Rainer

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