The present invention provides a data processing apparatus and method of controlling access to a shared resource. The data processing apparatus has a plurality of processors operable to perform respective data processing operations requiring access to the shared resource, and a path is provided interconnecting the plurality of processors. An access control mechanism is operable to control access to the shared resource by the plurality of processors, each processor being operable to enter a power saving mode if access to the shared resource is required but the access control mechanism is preventing access to the shared resource by that processor. Further, each processor is operable, when that processor has access to the shared resource, to issue a notification on the path when access to the shared resource is no longer required by that processor. A processor in the power saving mode is arranged, upon receipt of that notification, to exit the power saving mode and to seek access to the shared resource. This approach has been found to result in significant power savings.