drm/i915/gtt: Setup vm callbacks late

If we manage to tangle errorpaths and get call to callbacks,
it is better to defensively keep them as null until object init is
finished so that we get clean null deref on callsite,
instead of more cryptic wreckage with partly initialized vm objects.
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1488295691-9404-5-git-send-email-mika.kuoppala@intel.com

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -1338,11 +1338,6 @@ static int gen8_ppgtt_init(struct i915_hw_ppgtt *ppgtt)
 		return ret;
 	}
 
-	ppgtt->base.cleanup = gen8_ppgtt_cleanup;
-	ppgtt->base.unbind_vma = ppgtt_unbind_vma;
-	ppgtt->base.bind_vma = ppgtt_bind_vma;
-	ppgtt->debug_dump = gen8_dump_ppgtt;
-
 	/* There are only few exceptions for gen >=6. chv and bxt.
 	 * And we are not sure about the latter so play safe for now.
 	 */
@@ -1382,6 +1377,11 @@ static int gen8_ppgtt_init(struct i915_hw_ppgtt *ppgtt)
 	if (intel_vgpu_active(dev_priv))
 		gen8_ppgtt_notify_vgt(ppgtt, true);
 
+	ppgtt->base.cleanup = gen8_ppgtt_cleanup;
+	ppgtt->base.unbind_vma = ppgtt_unbind_vma;
+	ppgtt->base.bind_vma = ppgtt_bind_vma;
+	ppgtt->debug_dump = gen8_dump_ppgtt;
+
 	return 0;
 
 free_scratch:
@@ -1808,13 +1808,7 @@ static int gen6_ppgtt_init(struct i915_hw_ppgtt *ppgtt)
 	if (ret)
 		return ret;
 
-	ppgtt->base.clear_range = gen6_ppgtt_clear_range;
-	ppgtt->base.insert_entries = gen6_ppgtt_insert_entries;
-	ppgtt->base.unbind_vma = ppgtt_unbind_vma;
-	ppgtt->base.bind_vma = ppgtt_bind_vma;
-	ppgtt->base.cleanup = gen6_ppgtt_cleanup;
 	ppgtt->base.total = I915_PDES * GEN6_PTES * PAGE_SIZE;
-	ppgtt->debug_dump = gen6_dump_ppgtt;
 
 	gen6_scratch_va_range(ppgtt, 0, ppgtt->base.total);
 	gen6_write_page_range(ppgtt, 0, ppgtt->base.total);
@@ -1825,6 +1819,13 @@ static int gen6_ppgtt_init(struct i915_hw_ppgtt *ppgtt)
 		return ret;
 	}
 
+	ppgtt->base.clear_range = gen6_ppgtt_clear_range;
+	ppgtt->base.insert_entries = gen6_ppgtt_insert_entries;
+	ppgtt->base.unbind_vma = ppgtt_unbind_vma;
+	ppgtt->base.bind_vma = ppgtt_bind_vma;
+	ppgtt->base.cleanup = gen6_ppgtt_cleanup;
+	ppgtt->debug_dump = gen6_dump_ppgtt;
+
 	DRM_DEBUG_DRIVER("Allocated pde space (%lldM) at GTT entry: %llx\n",
 			 ppgtt->node.size >> 20,
 			 ppgtt->node.start / PAGE_SIZE);