drm/i915/execlists: Microoptimise execlists_cancel_port_request()

Just rearrange the code slightly to trim the number of iterations
required.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20170925124929.16974-1-chris@chris-wilson.co.ukReviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>

drivers/gpu/drm/i915/intel_lrc.c

@@ -571,14 +571,17 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 		execlists_submit_ports(engine);
 }
 
-static void execlist_cancel_port_requests(struct intel_engine_execlists *execlists)
+static void
+execlist_cancel_port_requests(struct intel_engine_execlists *execlists)
 {
-	unsigned int i;
-
-	for (i = 0; i < ARRAY_SIZE(execlists->port); i++)
-		i915_gem_request_put(port_request(&execlists->port[i]));
+	struct execlist_port *port = execlists->port;
+	unsigned int num_ports = ARRAY_SIZE(execlists->port);
 
-	memset(execlists->port, 0, sizeof(execlists->port));
+	while (num_ports-- && port_isset(port)) {
+		i915_gem_request_put(port_request(port));
+		memset(port, 0, sizeof(*port));
+		port++;
+	}
 }
 
 static void execlists_cancel_requests(struct intel_engine_cs *engine)
@@ -625,7 +628,7 @@ static void execlists_cancel_requests(struct intel_engine_cs *engine)
 
 	execlists->queue = RB_ROOT;
 	execlists->first = NULL;
-	GEM_BUG_ON(port_isset(&execlists->port[0]));
+	GEM_BUG_ON(port_isset(execlists->port));
 
 	/*
 	 * The port is checked prior to scheduling a tasklet, but