[Bug 36630] New: Radeon jittery post 2.6.35

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Wed Apr 27 05:10:29 PDT 2011


           Summary: Radeon jittery post 2.6.35
           Product: xorg
           Version: git
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Driver/Radeon
        AssignedTo: xorg-driver-ati at lists.x.org
        ReportedBy: aeriksson at fastmail.fm
         QAContact: xorg-team at lists.x.org

Created an attachment (id=46117)
 --> (https://bugs.freedesktop.org/attachment.cgi?id=46117)


I've found what I guess is a radeon (or drm/kms) regression post 2.6.35.
I've got my TV conneced to my RS690G over HDMI, and the display has
always been jittery after POST and at the GRUB screen. Pre-KMS, the X
server (or driver) got it sorted, and when KMS started the display
stabilized right after the kernel driver was initiated. However, post
2.6.35, I see the jitter is back.

I've spent the last month trying to bisect it, but pretty much failed.
It appears that versions closer to 2.6.38/39 are more prone to display
jitter, while 2.6.36 or so can have many successful runs. It also
appears to be related to device power-on order, or so I've come to
believe; A stable display can turn jittery, just by power cycling the TV. I'm
also fairly successful in stabilizing a jittery display by power cycling the

I've uploaded a video of a 38-rc8 boot:
which is mirrored here:

You'll see jitter at the POST screen and in GRUB. When KMS kicks in it
stabilizes, and when Freevo starts X, it's back to jitter. It's not freevo
related at all as a plain 'xinit' to a WM-less xterm causes the same effect.

The jitter is always of the same kind. It looks like an old tv set which
loses sync. The contents on the display is, for a split second, placed
at the wrong part of the screen (vertically and to some extent
horizontally), and every 5-15 seconds or so, there is a big reset when
the TV tries to restart things (I guess). At the resets, thee is a loud
'ping' in the nearby stereo too...

During the bisect  (and at 39-rc4) I've seen this both at the console
(post KMS) and in X, so I'm not sure where the error is. I hope some of
you can get a better idea of where to hunt for the bug by looking at the

Another observation is that, if left jittering for a while (say a few to ten
minutes), it usually, but not always, stop occurring.

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