drm/i915: Check engine->default_state mapping on module load

Check we can indeed acquire a WB mapping of the context image on module
load. Later this will give us the opportunity to validate that we can
switch from WC to WB as required.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180914123504.2062-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem.c

@@ -5416,6 +5416,7 @@ static int __intel_engines_record_defaults(struct drm_i915_private *i915)
 
 	for_each_engine(engine, i915, id) {
 		struct i915_vma *state;
+		void *vaddr;
 
 		state = to_intel_context(ctx, engine)->state;
 		if (!state)
@@ -5438,6 +5439,16 @@ static int __intel_engines_record_defaults(struct drm_i915_private *i915)
 			goto err_active;
 
 		engine->default_state = i915_gem_object_get(state->obj);
+
+		/* Check we can acquire the image of the context state */
+		vaddr = i915_gem_object_pin_map(engine->default_state,
+						I915_MAP_WB);
+		if (IS_ERR(vaddr)) {
+			err = PTR_ERR(vaddr);
+			goto err_active;
+		}
+
+		i915_gem_object_unpin_map(engine->default_state);
 	}
 
 	if (IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)) {