+ /* Not a clue what this is exactly. Without pointing it at a
+ * scratch page, VRAM->GART blits with M2MF (as in DDX DFS)
+ * cause IOMMU "read from address 0" errors (rh#561267)
+ */
+ nv_wr32(dev, 0x100c08, dev_priv->gart_info.sg_dummy_bus >> 8);
+
+ /* This is needed to get meaningful information from 100c90
+ * on traps. No idea what these values mean exactly. */