greybus: connection: add latency tag enable/disable callbacks

This patch adds a layered wrapper around optional latency tag
enable/disable commands to APBridge. When set APBridge and GPBridge will
insert timing information into reserved fields in the loopback response
header. Correspondingly when unset no timing information will be included
in the response payload.
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/connection.c

@@ -527,6 +527,38 @@ void gb_connection_destroy(struct gb_connection *connection)
 	device_unregister(&connection->dev);
 }
 
+void gb_connection_latency_tag_enable(struct gb_connection *connection)
+{
+	struct greybus_host_device *hd = connection->hd;
+	int ret;
+
+	if (!hd->driver->latency_tag_enable)
+		return;
+
+	ret = hd->driver->latency_tag_enable(hd, connection->hd_cport_id);
+	if (ret) {
+		dev_err(&connection->dev,
+			"failed to enable latency tag: %d\n", ret);
+	}
+}
+EXPORT_SYMBOL_GPL(gb_connection_latency_tag_enable);
+
+void gb_connection_latency_tag_disable(struct gb_connection *connection)
+{
+	struct greybus_host_device *hd = connection->hd;
+	int ret;
+
+	if (!hd->driver->latency_tag_disable)
+		return;
+
+	ret = hd->driver->latency_tag_disable(hd, connection->hd_cport_id);
+	if (ret) {
+		dev_err(&connection->dev,
+			"failed to disable latency tag: %d\n", ret);
+	}
+}
+EXPORT_SYMBOL_GPL(gb_connection_latency_tag_disable);
+
 void gb_hd_connections_exit(struct greybus_host_device *hd)
 {
 	struct gb_connection *connection;

drivers/staging/greybus/connection.h

@@ -66,4 +66,7 @@ void greybus_data_rcvd(struct greybus_host_device *hd, u16 cport_id,
 
 int gb_connection_bind_protocol(struct gb_connection *connection);
 
+void gb_connection_latency_tag_enable(struct gb_connection *connection);
+void gb_connection_latency_tag_disable(struct gb_connection *connection);
+
 #endif /* __CONNECTION_H */