In the Edit I/O Device <=> Processor Definitions dialog from Figure 3, you can check the Explicit device candidate list box. This selection fills the Partitions (all available) box with a list of partitions that are reachable for the current device. Adding partitions to the Partitions defined for device(s) box will create the explicit device candidate list for the current device. Only the partitions contained in this list may access the device.
For XMP processors, if devices are connected to a control unit which is shared between multiple channel subsystems, some (not all) of these devices may specify an explicit null device candidate list for one or more CSSs. If you define a null device candidate list of a device for a certain CSS, then no partition of this CSS may have access to the device. Specifying a null device candidate list in HCM means to check the Explicit device candidate list box without adding candidates to the Partitions defined for device(s) box.