I have HDMI video/audio out on my AMD 7660D GPU, running the 13.2 beta 7 Catalyst drivers. When I suspend for a long-ish period and resume, HDMI audio does not work. It's still detected and I can try to move streams to HDMI, but nothing outputs. (This doesn't happen if I suspend for a brief moment.) I haven't found any way to get it back without restarting. (I haven't tried re-logging in.) Any ideas as to what might be causing this?

Given that this appears to be triggered by suspend, it could very well be a bug in the Catalyst drivers.

Have you attempted logging out and reloading the Catalyst drivers, by removing the modules and loading them back in?

That's what I suspected. I haven't tried what you suggested because I don't know how to do that. Can you point me to some explanation of how to do so? Many thanks!

First you need to logout, then drop to init 3.
Then you need to login as root (or use sudo as a normal user) and run the following:

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rmmod fglrx
modprobe fglrx

Please note that those commands may not be entirely correct, and that you screen may go blank after completing the first command.
As such, you might want to run it as a single command:

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rmmod fglrx && sleep 10s && modprobe fglrx

Once completed, you can return to init 5, and login again.

Thanks for the help. I ended up just removing the binary blob altogether to see if my suspend issues would go away too. Neither did. Even running the open source Mesa drivers, HDMI doesn't work on resume.

Unusual. If you invoke a program directly against the HDMI audio output, such as aplay (with a *.wav file) does that work?

Given that changing drivers had no impact, and that it still works after a short period of suspend, but does not after a long period of suspend it could be a hardware/firmware/BIOS level issue.

That didn't work either. In fact, I just booted the KDE liveCD of opensuse 12.3 and it also fails to produce sound through HDMI after resume from suspend. It's probably a BIOS issue, which wouldn't surprise me given other issues I've had with this board. In case anyone is interested/experiencing same issue, it's an Asrock FM2A75 Pro4-M (socket FM2 for AMD Trinity).

I would suggest reporting the issue to ATI as they may be able to workaround the issue in their proprietary driver or encourage the manufacturer to release an updated BIOS.

For an update, I installed Kubuntu 13.04 beta and HDMI works after resuming from sleep, so the issue has to do with Kubuntu 12.10 (with KDE 4.10.1 enabled through backports). I'll file a bug.