[Bug 49193] New: random screen blackouts

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=49193

             Bug #: 49193
           Summary: random screen blackouts
    Classification: Unclassified
           Product: xorg
           Version: git
          Platform: x86-64 (AMD64)
        OS/Version: Linux (All)
            Status: NEW
          Severity: major
          Priority: medium
         Component: Driver/Radeon
        AssignedTo: xorg-driver-ati at lists.x.org
        ReportedBy: thomas at koeller.dyndns.org
         QAContact: xorg-team at lists.x.org


Created attachment 60636
  --> https://bugs.freedesktop.org/attachment.cgi?id=60636
X server log /w acceleration enabled

I am running the latest git (commit 0bda305f7ab2a4720b3fea3f318ab2a73be151e5)
version of driver/xf86-video-ati. My hardware is a RV280 AGP card, for details
see the attached X server log.

The problem I am facing: Whenever I run the X server with acceleration enabled
in the radeon driver (option 'NoAccel' set to 'off'), the screen turns black at
uneven intervals, most often for ~2s, sometimes longer, then it comes up again.
These events seem to happen randomly, but most often when the screen contents
change, and generally at a rate high enough to make the display entirely
unusable. Even typing a single character in a text window is often sufficient
to trigger a blackout.

I tried lots of driver option settings, such as the different AGPMode settings,
disabling DRI and RenderAccel, and more, but the only thing that makes the
problem disappear is to set the 'NoAccel' option to 'on' (or, for that matter,
changing to the unaccelerated 'fbdev' driver).

I recently switched from an older 1280x1024 flatscreen monitor to a new one
with 1920x1080 resolution. The problem was already present when I still used
the old monitor, but the blackouts occurred much less often, and so I got used
to ignoring them. I do not remember when I first noticed the problem, nor what
driver version I was running at that time.

If a blackout lasts long enough, my monitor complains about video timings that
are beyond its limits. As can be seen in the server logs, the preferred video
mode is 1920x1080 @ 60 fps. The monitor sometimes reports a vertical frequency
twice as high (120 Hz). Also, when I chvt to a text console (using a frame
buffer console via the fbcon kernel module), the blackouts keep occurring even
in text mode until I shut down the X server. I therefore suspect that the
problem is ultimatly caused by KMS malfunctioning.

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