drm/i915/execlists: Record elsp offset during engine setup

Currently, we record the elsp register offset inside init-hw but we only
need to do it once during engine setup (after we know the mmio
iomapping).
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NMichał Winiarski <michal.winiarski@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180102151235.3949-17-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_lrc.c

@@ -1496,9 +1496,6 @@ static int gen8_init_common_ring(struct intel_engine_cs *engine)
 	execlists->csb_head = -1;
 	execlists->active = 0;
 
-	execlists->elsp =
-		dev_priv->regs + i915_mmio_reg_offset(RING_ELSP(engine));
-
 	/* After a GPU reset, we may have requests to replay */
 	if (execlists->first)
 		tasklet_schedule(&execlists->tasklet);
@@ -2007,6 +2004,9 @@ static int logical_ring_init(struct intel_engine_cs *engine)
 	if (ret)
 		goto error;
 
+	engine->execlists.elsp =
+		engine->i915->regs + i915_mmio_reg_offset(RING_ELSP(engine));
+
 	return 0;
 
 error: