drm/ttm: restructure to allow driver to plug in alternate memory manager

Nouveau will need this on GeForce 8 and up to account for the GPU
reordering physical VRAM for some memory types.

Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Acked-by: Thomas Hellström <thellstrom@vmware.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/ttm/ttm_agp_backend.c b/drivers/gpu/drm/ttm/ttm_agp_backend.c
index 4bf69c4..f999e36 100644
--- a/drivers/gpu/drm/ttm/ttm_agp_backend.c
+++ b/drivers/gpu/drm/ttm/ttm_agp_backend.c
@@ -74,6 +74,7 @@
 {
 	struct ttm_agp_backend *agp_be =
 	    container_of(backend, struct ttm_agp_backend, backend);
+	struct drm_mm_node *node = bo_mem->mm_node;
 	struct agp_memory *mem = agp_be->mem;
 	int cached = (bo_mem->placement & TTM_PL_FLAG_CACHED);
 	int ret;
@@ -81,7 +82,7 @@
 	mem->is_flushed = 1;
 	mem->type = (cached) ? AGP_USER_CACHED_MEMORY : AGP_USER_MEMORY;
 
-	ret = agp_bind_memory(mem, bo_mem->mm_node->start);
+	ret = agp_bind_memory(mem, node->start);
 	if (ret)
 		printk(KERN_ERR TTM_PFX "AGP Bind memory failed.\n");