[Bug 88803] New: Resolution switch sometimes leads to corrupted or black screen on LVDS output

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=88803

            Bug ID: 88803
           Summary: Resolution switch sometimes leads to corrupted or
                    black screen on LVDS output
           Product: xorg
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Driver/Radeon
          Assignee: xorg-driver-ati at lists.x.org
          Reporter: j.stern at gsp-berlin.de
        QA Contact: xorg-team at lists.x.org

Sometimes after the first mode switch during booting our system, the LVDS
output shows a distorted picture which after some seconds disappears
completely. We were able to reproduce the problem in about 1 of 50 tries. The
higher the resolution, the more likely the error was. We could reproduce it
with xf86-video-ati 7.3.0 (Porteus Linux 3.0) and 7.5.0 (Porteus Linux 3.1rc2).
It does NOT happen with the Catalyst driver we used before.

We found the following 100% working fix which we unconditionally apply on every
boot (we cannot find out if the problem occured or not):

xrandr --output LVDS --off
sleep 1
xrandr --output LVDS --preferred

Omitting the "sleep 1" does NOT fix the problem. Because all of this, we
suspect it has something to do with how the driver switches from one resolution
to another, which also is a lot faster compared to when switching resolutions
with the Catalyst driver.

The hardware we use are different congatec conga-EAF ETX boards
(http://www.congatec.com/en/products/etx/conga-eaf.html) with AMD HD6320 and
AMD HD 6250 graphics. The board uses an Analogix ANX3110 DisplayPort to LVDS
converter, which we suspect cannot cope with the DisplayPort signal it gets. We
can rule out our custom base board as the problem also appears when using the
congatec evaluation board.

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