drm/i915/selftests: Err out on coherency if initialisation failed

If gt initialisation failed, we are left with no engines to use for
coherency testing. Currently we bug out, which makes the actual error,
so fail more gracefully instead.

Closes: https://gitlab.freedesktop.org/drm/intel/issues/896Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Andi Shyti <andi.shyti@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191227103050.2715402-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/selftests/i915_gem_coherency.c

@@ -325,7 +325,10 @@ static int igt_gem_coherency(void *arg)
 	values = offsets + ncachelines;
 
 	ctx.engine = random_engine(i915, &prng);
-	GEM_BUG_ON(!ctx.engine);
+	if (!ctx.engine) {
+		err = -ENODEV;
+		goto out_free;
+	}
 	pr_info("%s: using %s\n", __func__, ctx.engine->name);
 	intel_engine_pm_get(ctx.engine);
 
@@ -354,7 +357,7 @@ static int igt_gem_coherency(void *arg)
 					ctx.obj = i915_gem_object_create_internal(i915, PAGE_SIZE);
 					if (IS_ERR(ctx.obj)) {
 						err = PTR_ERR(ctx.obj);
-						goto free;
+						goto out_pm;
 					}
 
 					i915_random_reorder(offsets, ncachelines, &prng);
@@ -405,14 +408,15 @@ static int igt_gem_coherency(void *arg)
 			}
 		}
 	}
-free:
+out_pm:
 	intel_engine_pm_put(ctx.engine);
+out_free:
 	kfree(offsets);
 	return err;
 
 put_object:
 	i915_gem_object_put(ctx.obj);
-	goto free;
+	goto out_pm;
 }
 
 int i915_gem_coherency_live_selftests(struct drm_i915_private *i915)