drm/radeon/kms: block RN50 from using 3D engine.

RN50/ES1000 is a cut-down rv100 chip used in the server market.
The 3D engine on these is either not there or unverified so refuse
any attempt to configure registers on it.

Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/r100.c b/drivers/gpu/drm/radeon/r100.c
index 97c9229..0d05909 100644
--- a/drivers/gpu/drm/radeon/r100.c
+++ b/drivers/gpu/drm/radeon/r100.c
@@ -973,6 +973,11 @@
 		case R300_TX_OFFSET_0+52:
 		case R300_TX_OFFSET_0+56:
 		case R300_TX_OFFSET_0+60:
+			/* rn50 has no 3D engine so fail on any 3d setup */
+			if (ASIC_IS_RN50(p->rdev)) {
+				DRM_ERROR("attempt to use RN50 3D engine failed\n");
+				return -EINVAL;
+			}
 			r = r100_cs_packet_next_reloc(p, &reloc);
 			if (r) {
 				DRM_ERROR("No reloc for ib[%d]=0x%04X\n",