Comment 2 for bug 570589

@Jeremy:

I'm using the latest version of Ubuntu 10.04 and can test on three different machines, all of which exhibit the problem (two in extreme, one in not critical ways).
Upstream-testing is currently going on with the 2.6.34-series where some portions of the PM code have been added which already works. Further code is currently being prepared for merging into 2.6.35 once the merge window opens.
I tested this on all three machines with 2.6.34-rc5 and ATI KMS PM works when /etc/modprobe.d/radeon-kms.conf is altered to say "options radeon modeset=1 dynpm=1". On two machines dynamic clock setting works as it should, however on my main working machine (which doesn't get too hot on the 2600XT anyway) I need additional patches which allow me to manually set the clock speeds as dynpm doesn't work due to the settings in the atomBIOS table of my card.

So, in short: The issue has been fixed upstream (and is heavvily worked on right now) but is obviously missing from lucid's kernel.

To test the latest upstream PM code, apply these patches on top of the drm-next tree: http://people.freedesktop.org/~agd5f/pm3/