drm/i915: Move calling engine->init_hw() to its own function

Just a simple refactor to move a loop and some support code out of
i915_gem_init_hw(). This is in preparation for avoiding a race between
the tasklet writing to ELSP whilst simultaneously being written by
engine->init_hw() following a GPU reset.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170208143033.11651-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem.c

@@ -4367,11 +4367,24 @@ static void init_unused_rings(struct drm_i915_private *dev_priv)
 	}
 }
 
-int
-i915_gem_init_hw(struct drm_i915_private *dev_priv)
+static int __i915_gem_restart_engines(void *data)
 {
+	struct drm_i915_private *i915 = data;
 	struct intel_engine_cs *engine;
 	enum intel_engine_id id;
+	int err;
+
+	for_each_engine(engine, i915, id) {
+		err = engine->init_hw(engine);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
+int i915_gem_init_hw(struct drm_i915_private *dev_priv)
+{
 	int ret;
 
 	dev_priv->gt.last_init_time = ktime_get();
@@ -4417,11 +4430,9 @@ i915_gem_init_hw(struct drm_i915_private *dev_priv)
 	}
 
 	/* Need to do basic initialisation of all rings first: */
-	for_each_engine(engine, dev_priv, id) {
-		ret = engine->init_hw(engine);
+	ret = __i915_gem_restart_engines(dev_priv);
 	if (ret)
 		goto out;
-	}
 
 	intel_mocs_init_l3cc_table(dev_priv);