Glitch in newer drm-next/drm-radeon-testing

["Marius Gröger" <marius.groeger@googlemail.com>]

Hello All,

I'm trying the top-of-trunk drm-2.6 trees (both drm-next and
drm-radeon-testing) with my Radeon HD 3200 GPU over HDMI. The primary
application is mythtv which uses DRM syncing for the frame
syncronisation. Now, with the exact same userland software I noticed the
introduction of sync gliches in the May-timeframe. The
drm-radeon-testing on May 9 was still ok, but both drm-next and
drm-radeon-testing at the end of May showed that glitch: every couple of
seconds there's a very visual hickup, especially in scroll texts.

Apologies for such an unspecific description, and for what almost seems
like a support request for MythTV. I wouldn't post here if I were not
100% sure it must be related with the recent drm changes.

What I've tried so far:

* I tried bisecting, but I failed to spot the offending commits somehow.
My last hope is this list of experts - for me the git logs look sane,
but you guy surely have more insight.

* I tried turning on drm debug=1, but did not see anything suspicious,
especially with relation to the r600 irq handling changes.

* Currently I'm in the process of setting up systemtap to profile the
scheduling, but I'm still on the learning curve  :)

I'd be most grateful for any tips and things to try to isolate this issue.

Thanks
Marius