Comment # 18 on bug 91268 from Michel Dänzer

(In reply to Christian König from comment #11)
> Considering how old the hardware is I suggest that we just disable that
> feature for anything older than R7XX.

fglrx was already using write-combined CPU mappings with the very first PCIe
GPUs (RV3xx), so I don't think it's that simple.

I was hoping that we'd find something to key off a quirk in the dmesg output,
but since we can't seem to get that, maybe this is the best we can do for now.
:(