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+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+=======
+KHO FDT
+=======
+
+KHO uses the flattened device tree (FDT) container format and libfdt
+library to create and parse the data that is passed between the
+kernels. The properties in KHO FDT are stored in native format.
+It includes the physical address of an in-memory structure describing
+all preserved memory regions, as well as physical addresses of KHO users'
+own FDTs. Interpreting those sub FDTs is the responsibility of KHO users.
+
+KHO nodes and properties
+========================
+
+Property ``preserved-memory-map``
+---------------------------------
+
+KHO saves a special property named ``preserved-memory-map`` under the root node.
+This node contains the physical address of an in-memory structure for KHO to
+preserve memory regions across kexec.
+
+Property ``compatible``
+-----------------------
+
+The ``compatible`` property determines compatibility between the kernel
+that created the KHO FDT and the kernel that attempts to load it.
+If the kernel that loads the KHO FDT is not compatible with it, the entire
+KHO process will be bypassed.
+
+Property ``fdt``
+----------------
+
+Generally, a KHO user serialize its state into its own FDT and instructs
+KHO to preserve the underlying memory, such that after kexec, the new kernel
+can recover its state from the preserved FDT.
+
+A KHO user thus can create a node in KHO root tree and save the physical address
+of its own FDT in that node's property ``fdt`` .
+
+Examples
+========
+
+The following example demonstrates KHO FDT that preserves two memory
+regions created with ``reserve_mem`` kernel command line parameter::
+
+  /dts-v1/;
+
+  / {
+  	compatible = "kho-v1";
+
+	preserved-memory-map = <0x40be16 0x1000000>;
+
+  	memblock {
+		fdt = <0x1517 0x1000000>;
+  	};
+  };
+
+where the ``memblock`` node contains an FDT that is requested by the
+subsystem memblock for preservation. The FDT contains the following
+serialized data::
+
+  /dts-v1/;
+
+  / {
+  	compatible = "memblock-v1";
+
+  	n1 {
+  		compatible = "reserve-mem-v1";
+  		start = <0xc06b 0x4000000>;
+  		size = <0x04 0x00>;
+  	};
+
+  	n2 {
+  		compatible = "reserve-mem-v1";
+  		start = <0xc067 0x4000000>;
+  		size = <0x04 0x00>;
+  	};
+  };