greybus: time out operation requests

Arrange for operation requests that takke too long to time out.
At the moment, nothing happens when that occurs (other than a silly
message getting printed).  When the connection and operation and
interface and module code are cleaned up properly, this event should
most likely cause the affected module to get torn down.
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

drivers/staging/greybus/connection.c

@@ -102,6 +102,15 @@ static void gb_connection_hd_cport_id_free(struct gb_connection *connection)
 	connection->hd_cport_id = CPORT_ID_BAD;
 }
 
+static void connection_timeout(struct work_struct *work)
+{
+	struct gb_connection *connection;
+
+	connection =
+		container_of(work, struct gb_connection, timeout_work.work);
+	printk("timeout!\n");
+}
+
 /*
  * Set up a Greybus connection, representing the bidirectional link
  * between a CPort on a (local) Greybus host device and a CPort on
@@ -143,6 +152,7 @@ struct gb_connection *gb_connection_create(struct gb_interface *interface,
 	INIT_LIST_HEAD(&connection->operations);
 	connection->pending = RB_ROOT;
 	atomic_set(&connection->op_cycle, 0);
+	INIT_DELAYED_WORK(&connection->timeout_work, connection_timeout);
 
 	return connection;
 }

drivers/staging/greybus/connection.h

@@ -26,6 +26,7 @@ struct gb_connection {
 	struct list_head		operations;
 	struct rb_root			pending;	/* awaiting reponse */
 	atomic_t			op_cycle;
+	struct delayed_work		timeout_work;
 
 	void				*private;
 };

drivers/staging/greybus/operation.c

@@ -19,6 +19,8 @@
  */
 #define GB_OPERATION_TYPE_RESPONSE	0x80
 
+#define CONNECTION_TIMEOUT_DEFAULT	1000	/* milliseconds */
+
 /*
  * XXX This needs to be coordinated with host driver parameters
  */
@@ -62,6 +64,8 @@ static void gb_operation_insert(struct gb_operation *operation)
 	struct rb_node **link = &root->rb_node;
 	struct rb_node *above = NULL;
 	struct gb_operation_msg_hdr *header;
+	unsigned long timeout;
+	bool start_timer;
 	__le16 wire_id;
 
 	/*
@@ -76,6 +80,16 @@ static void gb_operation_insert(struct gb_operation *operation)
 	/* OK, insert the operation into its connection's tree */
 	spin_lock_irq(&gb_operations_lock);
 
+	/*
+	 * We impose a time limit for requests to complete.  If
+	 * there are no requests pending there is no need for a
+	 * timer.  So if this will be the only one in flight we'll
+	 * need to start the timer.  Otherwise we just update the
+	 * existing one to give this request a full timeout period
+	 * to complete.
+	 */
+	start_timer = RB_EMPTY_ROOT(root);
+
 	while (*link) {
 		struct gb_operation *other;
 
@@ -89,15 +103,31 @@ static void gb_operation_insert(struct gb_operation *operation)
 	}
 	rb_link_node(node, above, link);
 	rb_insert_color(node, root);
-
 	spin_unlock_irq(&gb_operations_lock);
+
+	timeout = msecs_to_jiffies(CONNECTION_TIMEOUT_DEFAULT);
+	if (start_timer)
+		schedule_delayed_work(&connection->timeout_work, timeout);
+	else
+		mod_delayed_work(system_wq, &connection->timeout_work, timeout);
 }
 
 static void gb_operation_remove(struct gb_operation *operation)
 {
+	struct gb_connection *connection = operation->connection;
+	bool last_pending;
+
 	spin_lock_irq(&gb_operations_lock);
-	rb_erase(&operation->node, &operation->connection->pending);
+	rb_erase(&operation->node, &connection->pending);
+	last_pending = RB_EMPTY_ROOT(&connection->pending);
 	spin_unlock_irq(&gb_operations_lock);
+
+	/*
+	 * If there are no more pending requests, we can stop the
+	 * timeout timer.
+	 */
+	if (last_pending)
+		cancel_delayed_work(&connection->timeout_work);
 }
 
 static struct gb_operation *