so all the other drivers (intel, nouveau) seem to pass the ELD stuff into the hardware at some point, not sure if you can work out from radeontool or you need more tracing to see if this happens on ATI hw.
I had an HD 5850 for a year, doing almost exclusive Windows gaming and when switching back to works on Linux, I sold it. One year after being sold, it is still not supported by Linux, it proved again that ATI is for Windows only and investing on hardware for the future support is the stupidest idea.
It's completely family dependant (and also timing dependant) best is to not read this range, also the way radeontool hamer the register backbone doesn't help.
Unfortunately I can't limit the range of registers. I'm blindly looking for registers used for controlling HDMI (enabling HDMI mode, setting audio and video frames).
Even worse: from the early results I've received, it seems DCE4 (early Evergreen) does not have HDMI registers in 0x0000...0xe000.