Thanks for your efforts oibaf.
I also want to thank you :) Couldn't use 12.04 because a bug somehwere in the radeon stack kept locking my PC up randomly. Using your updated packages gave me a stable system :)
I switched from a hd4770 to a hd3850 and now my KDE turn into black screen with a running mouse (strg+alt+f1 console also works).
only the KDE-save-mode runs.. maybe the desktop 3D kwin are broken for hd3850 ? and with a hd4770 it works..
Also see my previous post about disabling LLVM.
I'm using xserver-xorg-video-ati 1:6.14.99+git1206080959.588837~gd~o in Mythbuntu 12.04 with a VisionTek Radeon HD2600 Pro AGP, a Soltek SL-65KVB motherboard and a 1 GHz Pentium 3. OpenGL and VDPAU output is capped to 10 fps, as if the vertical refresh rate is 10 Hz. However, it is actually 60 Hz, and xrandr properly outputs that.
Glxgears runs at 10 fps unless I have a vblank_mode=0 environment variable or I set the same thing via .drirc. (Driconf does not change anything unless ~/.drirc it creates is edited to change driver at the top to "dri2".) When I make that change, it runs at close to 200 FPS. Mplayer OpenGL output also runs at 10 fps unless I use "-vo gl:swapinterval=0". Interestingly, I don't see any tearing after changing those options.
VDPAU is useless because it is always capped to 10 fps and I don't know how to change that.
When MythTV is outputting video via XVideo at 30 fps, there is severe judder. Smooth pans have a very regular pattern of slowing down and speeding up. This problem goes away if I select one of the 2x deinterlacers and output at 60 fps. This is not exactly a 10 fps cap, but it may have something to do with this issue.
None of these problems are present in the driver that comes with 12.04.