Hi. i am just an user of rv280 and mostly current linux stack.
Draw operation with KMS are deadly slow, so don't look in that code. I think devs just get it for free from Xorg's acceleration architecture
, so it remain in software - no GPU accelaration.
It is better with UMS and EXA and even faster with now removed XAA.
P.S. No, no, i'm not sarcastic, rv280 is just unusable with current stack.