This is necessary for AGP to work after running bios init scripts on nv3x, and
is seen in mmio traces of all cards (nv04-nv4x)
I'm not making the equivalent change to nv40_mc.c, as early cards (6200, 6800gt)
use the 0x000018XX PBUS and later cards use the 0x000880XX PBUS and I don't know
the effects of using the wrong one
The PGRAPH init for the various cards will need cleaning up at some point,
a lot of the values written there are per-context state left over from the
all the hardcoding done in the ddx.
It's possible some cards get broken by this commit, let me know.
Tested on: NV5, NV18, NV28, NV35, NV40, NV4E
Stuart Bennett
Dave Airlie
Ben Skeggs