If you had hdmi audio working in Slackware 14.0 and it not working in 14.1 with your card that uses the radeon module, you probably need to load the module with the argument.
If you load it from initrd you might have to modify /boot/initrd-tree/load_kernel_modules and rebuild your initrd, and update lilo.
Somewhere along the line of kernels between 3.2 and 3.10 it started defaulting to disabled. Lots about that on Google. I had trouble finding the cause because appears to work, alsa will show the audio card present and the hdmi subdevice even when disabled. So I thought I'd share here. Audio applications will appear to be playing you just won't hear anything. I can't find anything that indicates its disabled, but don't be fooled. Make sure the argument is passed and suddenly everything works.