So while I suspect this is a topic that's been beaten to death and on which there should be plenty to read about, I still am not sure what the real difference between the radeon & the radeonhd drivers are. I know that the 'hd' one is supposed to be a rewrite ? ... and that it's supposed to be for cards from r500 and onwards ...
But other than that, I fail to find any information as to where the radeonhd driver is at, or whether on which one I should be using and why ? ... Ive been the project page for radeonhd but nothing there could answer any of my questions.
Note also that I have an r500 card and that the radeonhd driver just doesn't work on my laptop.
He meant that you still can use xf86-video-ati driver. You never said it doesn't work, only that xf86-video-radeonhd doesn't work. He meant that not everyone is lucky to enough to be supported by *two* opensource drivers. (Though nowadays probably only people with older cards than r500 aren't)
I currently own a card which would work with radeonhd, but I think it is wasted time to use it, because autodetection is forcing ati/radeon and radeonhd will be always 2nd choice only. The automatically used driver has to work.
To my knowledge, the only thing radeonhd does at all that the radeon driver does not is support of HDMI Audio. I'm quite sure that'll end up in the radeon driver as well if/when someone actually bothers to port the patches.
Otherwise, the drivers have pretty closely aligned. The radeonhd driver used to do things totally differently than the radeon driver, but that changed iirc after the radeon approach (using AtomBIOS) was proven pretty much mandatory for supporting all the new cards.
The modesetting code is still fairly different, even in the cases where both drivers use AtomBIOS (7xx and up). We're still finding a number of cases where one driver works and the other doesn't, and having the two code paths often helps to track down the issue. When we find that both drivers have the same problems, that's our cue to go looking for hardware workarounds in the closed-source drivers.
Our guess is that the benefit from having two drivers will fade out around the same time that kernel modesetting becomes commonplace in shipping distros, ie sometime in 2010. In the meantime, most of the ongoing work is done outside of the X driver (ie in drm and mesa), so there isn't much additional overhead from having the two drivers.