docs(genesis): define s390x validation limits

docs/source/developers/guides/code/dhcp_backend_validation_matrix.rst

@@ -136,6 +136,12 @@ The following matrix is the default live validation gate for DHCP backend work.
      - ``makedhcp -n``; backend parser; architecture ``0x001f``; DHCP options
        209 and 210; TFTP fetch of the generated ``pxelinux.cfg``-style configuration,
        Genesis kernel, and initramfs
+   * - IBM Z DPM
+     - ``s390x``
+     - ``ISC`` and ``Kea``
+     - configuration handoff only
+     - backend parser; architecture ``0x0020``; generated network configuration
+       offered as the DHCP boot filename; physical boot remains unvalidated
 
 Kea Boot and Reservation Regression Matrix
 ------------------------------------------

docs/source/developers/guides/code/genesis_openembedded_plan.rst

@@ -99,6 +99,8 @@ and z/VM Genesis networking therefore remain unvalidated.
 Genesis does not use the shared CEC serial as an s390x node identifier.
 QEMU validation covers network IPL, DHCP options 209 and 210, TFTP, and the
 network-specific ``pxelinux.cfg``-style configuration written by ``mknb``.
+For DPM clients, DHCP architecture 32 receives a DPM-formatted configuration
+as its boot filename.  This path has parser coverage but no physical validation.
 Existing xCAT s390x operating-system provisioning remains unchanged.
 
 xCAT protocol
@@ -283,6 +285,8 @@ References
   <https://kas.readthedocs.io/en/latest/userguide/project-configuration.html>`_
 * `NetworkManager dispatcher interface
   <https://networkmanager.dev/docs/api/latest/NetworkManager-dispatcher.html>`_
+* `IBM Z DPM network boot server configuration
+  <https://www.ibm.com/docs/en/systems-hardware/zsystems/2964-N63?topic=administrators-customizing-network-boot-server-environment>`_
 * `NetworkManager initrd generator
   <https://networkmanager.dev/docs/api/latest/nm-initrd-generator.html>`_
 * `systemd system extensions