Booting the Linux/ppc kernel without Open Firmware
             --------------------------------------------------

  (c) 2005 Benjamin Herrenschmidt <benh at kernel.crashing.org>,
      IBM Corp.
  (c) 2005 Becky Bruce <becky.bruce at freescale.com>,
      Freescale Semiconductor, FSL SOC and 32-bit additions

  (c) 2006 MontaVista Software, Inc.
      Flash chip node definition

  Table of Contents
  =================
  
    I - Introduction

      1) Entry point for arch/arm
      2) Entry point for arch/powerpc
      3) Entry point for arch/x86

  
    II - The DT block format
      1) Header
      2) Device tree generalities
      3) Device tree "structure" block
      4) Device tree "strings" block
  
    III - Required content of the device tree
      1) Note about cells and address representation
      2) Note about "compatible" properties
      3) Note about "name" properties
      4) Note about node and property names and character set
      5) Required nodes and properties
        a) The root node
        b) The /cpus node
        c) The /cpus/* nodes
        d) the /memory node(s)
        e) The /chosen node
        f) the /soc<SOCname> node
  
    IV - "dtc", the device tree compiler
  
    V - Recommendations for a bootloader
  
    VI - System-on-a-chip devices and nodes
      1) Defining child nodes of an SOC
      2) Representing devices without a current OF specification

    VII - Specifying interrupt information for devices

      1) interrupts property
      2) interrupt-parent property
      3) OpenPIC Interrupt Controllers
      4) ISA Interrupt Controllers

    VIII - Specifying device power management information (sleep property)

    Appendix A - Sample SOC node for MPC8540
  
  
  Revision Information
  ====================

     May 18, 2005: Rev 0.1 - Initial draft, no chapter III yet.
  
     May 19, 2005: Rev 0.2 - Add chapter III and bits & pieces here or
                             clarifies the fact that a lot of things are
                             optional, the kernel only requires a very
                             small device tree, though it is encouraged
                             to provide an as complete one as possible.
  
     May 24, 2005: Rev 0.3 - Precise that DT block has to be in RAM
  			 - Misc fixes
  			 - Define version 3 and new format version 16
  			   for the DT block (version 16 needs kernel
  			   patches, will be fwd separately).
  			   String block now has a size, and full path
  			   is replaced by unit name for more
  			   compactness.
  			   linux,phandle is made optional, only nodes
  			   that are referenced by other nodes need it.
  			   "name" property is now automatically
  			   deduced from the unit name
  
     June 1, 2005: Rev 0.4 - Correct confusion between OF_DT_END and
                             OF_DT_END_NODE in structure definition.
                           - Change version 16 format to always align
                             property data to 4 bytes. Since tokens are
                             already aligned, that means no specific

                             required alignment between property size

                             and property data. The old style variable
                             alignment would make it impossible to do
                             "simple" insertion of properties using

                             memmove (thanks Milton for

                             noticing). Updated kernel patch as well

  			 - Correct a few more alignment constraints

  			 - Add a chapter about the device-tree
                             compiler and the textural representation of
                             the tree that can be "compiled" by dtc.

     November 21, 2005: Rev 0.5
  			 - Additions/generalizations for 32-bit
  			 - Changed to reflect the new arch/powerpc
  			   structure
  			 - Added chapter VI
  
  
   ToDo:
  	- Add some definitions of interrupt tree (simple/complex)

  	- Add some definitions for PCI host bridges

  	- Add some common address format examples
  	- Add definitions for standard properties and "compatible"
  	  names for cells that are not already defined by the existing
  	  OF spec.
  	- Compare FSL SOC use of PCI to standard and make sure no new
  	  node definition required.
  	- Add more information about node definitions for SOC devices
    	  that currently have no standard, like the FSL CPM.
  
  
  I - Introduction
  ================

  During the development of the Linux/ppc64 kernel, and more

  specifically, the addition of new platform types outside of the old
  IBM pSeries/iSeries pair, it was decided to enforce some strict rules
  regarding the kernel entry and bootloader <-> kernel interfaces, in
  order to avoid the degeneration that had become the ppc32 kernel entry
  point and the way a new platform should be added to the kernel. The
  legacy iSeries platform breaks those rules as it predates this scheme,
  but no new board support will be accepted in the main tree that

  doesn't follow them properly.  In addition, since the advent of the

  arch/powerpc merged architecture for ppc32 and ppc64, new 32-bit
  platforms and 32-bit platforms which move into arch/powerpc will be
  required to use these rules as well.
  
  The main requirement that will be defined in more detail below is
  the presence of a device-tree whose format is defined after Open
  Firmware specification. However, in order to make life easier
  to embedded board vendors, the kernel doesn't require the device-tree
  to represent every device in the system and only requires some nodes
  and properties to be present. This will be described in detail in
  section III, but, for example, the kernel does not require you to
  create a node for every PCI device in the system. It is a requirement
  to have a node for PCI host bridges in order to provide interrupt

  routing information and memory/IO ranges, among others. It is also

  recommended to define nodes for on chip devices and other buses that

  don't specifically fit in an existing OF specification. This creates a
  great flexibility in the way the kernel can then probe those and match
  drivers to device, without having to hard code all sorts of tables. It
  also makes it more flexible for board vendors to do minor hardware
  upgrades without significantly impacting the kernel code or cluttering
  it with special cases.

  1) Entry point for arch/arm
  ---------------------------
  
     There is one single entry point to the kernel, at the start
     of the kernel image. That entry point supports two calling
     conventions.  A summary of the interface is described here.  A full
     description of the boot requirements is documented in
     Documentation/arm/Booting
  
          a) ATAGS interface.  Minimal information is passed from firmware
          to the kernel with a tagged list of predefined parameters.
  
                  r0 : 0
  
                  r1 : Machine type number
  
                  r2 : Physical address of tagged list in system RAM
  
          b) Entry with a flattened device-tree block.  Firmware loads the
          physical address of the flattened device tree block (dtb) into r2,
          r1 is not used, but it is considered good practise to use a valid
          machine number as described in Documentation/arm/Booting.
  
                  r0 : 0
  
                  r1 : Valid machine type number.  When using a device tree,
                  a single machine type number will often be assigned to
                  represent a class or family of SoCs.
  
                  r2 : physical pointer to the device-tree block
                  (defined in chapter II) in RAM.  Device tree can be located
                  anywhere in system RAM, but it should be aligned on a 64 bit
                  boundary.
  
     The kernel will differentiate between ATAGS and device tree booting by
     reading the memory pointed to by r2 and looking for either the flattened
     device tree block magic value (0xd00dfeed) or the ATAG_CORE value at
     offset 0x4 from r2 (0x54410001).
  
  2) Entry point for arch/powerpc

  -------------------------------

     There is one single entry point to the kernel, at the start

     of the kernel image. That entry point supports two calling
     conventions:
  
          a) Boot from Open Firmware. If your firmware is compatible
          with Open Firmware (IEEE 1275) or provides an OF compatible
          client interface API (support for "interpret" callback of
          forth words isn't required), you can enter the kernel with:
  
                r5 : OF callback pointer as defined by IEEE 1275

                bindings to powerpc. Only the 32-bit client interface

                is currently supported
  
                r3, r4 : address & length of an initrd if any or 0
  
                The MMU is either on or off; the kernel will run the
                trampoline located in arch/powerpc/kernel/prom_init.c to
                extract the device-tree and other information from open
                firmware and build a flattened device-tree as described
                in b). prom_init() will then re-enter the kernel using
                the second method. This trampoline code runs in the
                context of the firmware, which is supposed to handle all
                exceptions during that time.
  
          b) Direct entry with a flattened device-tree block. This entry
          point is called by a) after the OF trampoline and can also be
          called directly by a bootloader that does not support the Open
          Firmware client interface. It is also used by "kexec" to
          implement "hot" booting of a new kernel from a previous
          running one. This method is what I will describe in more
          details in this document, as method a) is simply standard Open
          Firmware, and thus should be implemented according to the
          various standard documents defining it and its binding to the
          PowerPC platform. The entry point definition then becomes:
  
                  r3 : physical pointer to the device-tree block
                  (defined in chapter II) in RAM
  
                  r4 : physical pointer to the kernel itself. This is
                  used by the assembly code to properly disable the MMU
                  in case you are entering the kernel with MMU enabled
                  and a non-1:1 mapping.

                  r5 : NULL (as to differentiate with method a)

  
          Note about SMP entry: Either your firmware puts your other
          CPUs in some sleep loop or spin loop in ROM where you can get
          them out via a soft reset or some other means, in which case
          you don't need to care, or you'll have to enter the kernel
          with all CPUs. The way to do that with method b) will be
          described in a later revision of this document.

     Board supports (platforms) are not exclusive config options. An
     arbitrary set of board supports can be built in a single kernel
     image. The kernel will "know" what set of functions to use for a
     given platform based on the content of the device-tree. Thus, you
     should:
  
          a) add your platform support as a _boolean_ option in
          arch/powerpc/Kconfig, following the example of PPC_PSERIES,
          PPC_PMAC and PPC_MAPLE. The later is probably a good
          example of a board support to start from.
  
          b) create your main platform file as
          "arch/powerpc/platforms/myplatform/myboard_setup.c" and add it
          to the Makefile under the condition of your CONFIG_
          option. This file will define a structure of type "ppc_md"
          containing the various callbacks that the generic code will
          use to get to your platform specific code

    A kernel image may support multiple platforms, but only if the

    platforms feature the same core architecture.  A single kernel build

    cannot support both configurations with Book E and configurations
    with classic Powerpc architectures.

  3) Entry point for arch/x86

  -------------------------------
  
    There is one single 32bit entry point to the kernel at code32_start,
    the decompressor (the real mode entry point goes to the same  32bit
    entry point once it switched into protected mode). That entry point
    supports one calling convention which is documented in
    Documentation/x86/boot.txt
    The physical pointer to the device-tree block (defined in chapter II)
    is passed via setup_data which requires at least boot protocol 2.09.
    The type filed is defined as
  
    #define SETUP_DTB                      2
  
    This device-tree is used as an extension to the "boot page". As such it
    does not parse / consider data which is already covered by the boot
    page. This includes memory size, reserved ranges, command line arguments
    or initrd address. It simply holds information which can not be retrieved
    otherwise like interrupt routing or a list of devices behind an I2C bus.

  
  II - The DT block format
  ========================
  
  
  This chapter defines the actual format of the flattened device-tree
  passed to the kernel. The actual content of it and kernel requirements
  are described later. You can find example of code manipulating that
  format in various places, including arch/powerpc/kernel/prom_init.c
  which will generate a flattened device-tree from the Open Firmware
  representation, or the fs2dt utility which is part of the kexec tools
  which will generate one from a filesystem representation. It is
  expected that a bootloader like uboot provides a bit more support,
  that will be discussed later as well.
  
  Note: The block has to be in main memory. It has to be accessible in
  both real mode and virtual mode with no mapping other than main
  memory. If you are writing a simple flash bootloader, it should copy
  the block to RAM before passing it to the kernel.
  
  
  1) Header
  ---------

     The kernel is passed the physical address pointing to an area of memory
     that is roughly described in include/linux/of_fdt.h by the structure

     boot_param_header:
  
  struct boot_param_header {
          u32     magic;                  /* magic word OF_DT_HEADER */
          u32     totalsize;              /* total size of DT block */
          u32     off_dt_struct;          /* offset to structure */
          u32     off_dt_strings;         /* offset to strings */
          u32     off_mem_rsvmap;         /* offset to memory reserve map

                                             */

          u32     version;                /* format version */
          u32     last_comp_version;      /* last compatible version */
  
          /* version 2 fields below */
          u32     boot_cpuid_phys;        /* Which physical CPU id we're
                                             booting on */
          /* version 3 fields below */
          u32     size_dt_strings;        /* size of the strings block */

  
          /* version 17 fields below */
          u32	size_dt_struct;		/* size of the DT structure block */

  };
  
     Along with the constants:
  
  /* Definitions used by the flattened device tree */
  #define OF_DT_HEADER            0xd00dfeed      /* 4: version,
  						   4: total size */
  #define OF_DT_BEGIN_NODE        0x1             /* Start node: full name

  						   */

  #define OF_DT_END_NODE          0x2             /* End node */
  #define OF_DT_PROP              0x3             /* Property: name off,
                                                     size, content */
  #define OF_DT_END               0x9
  
     All values in this header are in big endian format, the various
     fields in this header are defined more precisely below. All
     "offset" values are in bytes from the start of the header; that is

     from the physical base address of the device tree block.

  
     - magic
  
       This is a magic value that "marks" the beginning of the
       device-tree block header. It contains the value 0xd00dfeed and is
       defined by the constant OF_DT_HEADER
  
     - totalsize
  
       This is the total size of the DT block including the header. The
       "DT" block should enclose all data structures defined in this
       chapter (who are pointed to by offsets in this header). That is,
       the device-tree structure, strings, and the memory reserve map.
  
     - off_dt_struct
  
       This is an offset from the beginning of the header to the start
       of the "structure" part the device tree. (see 2) device tree)
  
     - off_dt_strings
  
       This is an offset from the beginning of the header to the start
       of the "strings" part of the device-tree
  
     - off_mem_rsvmap
  
       This is an offset from the beginning of the header to the start

       of the reserved memory map. This map is a list of pairs of 64-

       bit integers. Each pair is a physical address and a size. The

       list is terminated by an entry of size 0. This map provides the
       kernel with a list of physical memory areas that are "reserved"
       and thus not to be used for memory allocations, especially during
       early initialization. The kernel needs to allocate memory during
       boot for things like un-flattening the device-tree, allocating an
       MMU hash table, etc... Those allocations must be done in such a
       way to avoid overriding critical things like, on Open Firmware
       capable machines, the RTAS instance, or on some pSeries, the TCE
       tables used for the iommu. Typically, the reserve map should
       contain _at least_ this DT block itself (header,total_size). If
       you are passing an initrd to the kernel, you should reserve it as
       well. You do not need to reserve the kernel image itself. The map

       should be 64-bit aligned.

  
     - version
  
       This is the version of this structure. Version 1 stops
       here. Version 2 adds an additional field boot_cpuid_phys.
       Version 3 adds the size of the strings block, allowing the kernel
       to reallocate it easily at boot and free up the unused flattened
       structure after expansion. Version 16 introduces a new more
       "compact" format for the tree itself that is however not backward

       compatible. Version 17 adds an additional field, size_dt_struct,
       allowing it to be reallocated or moved more easily (this is
       particularly useful for bootloaders which need to make
       adjustments to a device tree based on probed information). You
       should always generate a structure of the highest version defined
       at the time of your implementation. Currently that is version 17,
       unless you explicitly aim at being backward compatible.

  
     - last_comp_version
  
       Last compatible version. This indicates down to what version of
       the DT block you are backward compatible. For example, version 2
       is backward compatible with version 1 (that is, a kernel build
       for version 1 will be able to boot with a version 2 format). You
       should put a 1 in this field if you generate a device tree of

       version 1 to 3, or 16 if you generate a tree of version 16 or 17

       using the new unit name format.
  
     - boot_cpuid_phys
  
       This field only exist on version 2 headers. It indicate which
       physical CPU ID is calling the kernel entry point. This is used,
       among others, by kexec. If you are on an SMP system, this value
       should match the content of the "reg" property of the CPU node in
       the device-tree corresponding to the CPU calling the kernel entry

       point (see further chapters for more information on the required

       device-tree contents)

     - size_dt_strings
  
       This field only exists on version 3 and later headers.  It
       gives the size of the "strings" section of the device tree (which
       starts at the offset given by off_dt_strings).
  
     - size_dt_struct
  
       This field only exists on version 17 and later headers.  It gives
       the size of the "structure" section of the device tree (which
       starts at the offset given by off_dt_struct).

  
     So the typical layout of a DT block (though the various parts don't
     need to be in that order) looks like this (addresses go from top to
     bottom):
  
  
               ------------------------------

       base -> |  struct boot_param_header  |

               ------------------------------
               |      (alignment gap) (*)   |
               ------------------------------
               |      memory reserve map    |
               ------------------------------
               |      (alignment gap)       |
               ------------------------------
               |                            |
               |    device-tree structure   |
               |                            |
               ------------------------------
               |      (alignment gap)       |
               ------------------------------
               |                            |
               |     device-tree strings    |
               |                            |
        -----> ------------------------------
        |
        |

        --- (base + totalsize)

  
    (*) The alignment gaps are not necessarily present; their presence
        and size are dependent on the various alignment requirements of
        the individual data blocks.
  
  
  2) Device tree generalities
  ---------------------------
  
  This device-tree itself is separated in two different blocks, a
  structure block and a strings block. Both need to be aligned to a 4
  byte boundary.
  
  First, let's quickly describe the device-tree concept before detailing
  the storage format. This chapter does _not_ describe the detail of the
  required types of nodes & properties for the kernel, this is done
  later in chapter III.
  
  The device-tree layout is strongly inherited from the definition of
  the Open Firmware IEEE 1275 device-tree. It's basically a tree of
  nodes, each node having two or more named properties. A property can
  have a value or not.
  
  It is a tree, so each node has one and only one parent except for the
  root node who has no parent.
  
  A node has 2 names. The actual node name is generally contained in a
  property of type "name" in the node property list whose value is a
  zero terminated string and is mandatory for version 1 to 3 of the

  format definition (as it is in Open Firmware). Version 16 makes it

  optional as it can generate it from the unit name defined below.

  There is also a "unit name" that is used to differentiate nodes with

  the same name at the same level, it is usually made of the node

  names, the "@" sign, and a "unit address", which definition is

  specific to the bus type the node sits on.
  
  The unit name doesn't exist as a property per-se but is included in
  the device-tree structure. It is typically used to represent "path" in
  the device-tree. More details about the actual format of these will be
  below.

  The kernel generic code does not make any formal use of the

  unit address (though some board support code may do) so the only real
  requirement here for the unit address is to ensure uniqueness of
  the node unit name at a given level of the tree. Nodes with no notion
  of address and no possible sibling of the same name (like /memory or
  /cpus) may omit the unit address in the context of this specification,
  or use the "@0" default unit address. The unit name is used to define
  a node "full path", which is the concatenation of all parent node
  unit names separated with "/".
  
  The root node doesn't have a defined name, and isn't required to have
  a name property either if you are using version 3 or earlier of the
  format. It also has no unit address (no @ symbol followed by a unit
  address). The root node unit name is thus an empty string. The full
  path to the root node is "/".
  
  Every node which actually represents an actual device (that is, a node
  which isn't only a virtual "container" for more nodes, like "/cpus"

  is) is also required to have a "compatible" property indicating the
  specific hardware and an optional list of devices it is fully
  backwards compatible with.

  
  Finally, every node that can be referenced from a property in another

  node is required to have either a "phandle" or a "linux,phandle"
  property. Real Open Firmware implementations provide a unique
  "phandle" value for every node that the "prom_init()" trampoline code
  turns into "linux,phandle" properties. However, this is made optional
  if the flattened device tree is used directly. An example of a node

  referencing another node via "phandle" is when laying out the
  interrupt tree which will be described in a further version of this
  document.

  The "phandle" property is a 32-bit value that uniquely

  identifies a node. You are free to use whatever values or system of
  values, internal pointers, or whatever to generate these, the only
  requirement is that every node for which you provide that property has
  a unique value for it.
  
  Here is an example of a simple device-tree. In this example, an "o"
  designates a node followed by the node unit name. Properties are
  presented with their name followed by their content. "content"
  represents an ASCII string (zero terminated) value, while <content>

  represents a 32-bit hexadecimal value. The various nodes in this

  example will be discussed in a later chapter. At this point, it is
  only meant to give you a idea of what a device-tree looks like. I have
  purposefully kept the "name" and "linux,phandle" properties which
  aren't necessary in order to give you a better idea of what the tree
  looks like in practice.
  
    / o device-tree
        |- name = "device-tree"
        |- model = "MyBoardName"
        |- compatible = "MyBoardFamilyName"
        |- #address-cells = <2>
        |- #size-cells = <2>
        |- linux,phandle = <0>
        |
        o cpus
        | | - name = "cpus"
        | | - linux,phandle = <1>
        | | - #address-cells = <1>
        | | - #size-cells = <0>
        | |
        | o PowerPC,970@0
        |   |- name = "PowerPC,970"
        |   |- device_type = "cpu"
        |   |- reg = <0>
        |   |- clock-frequency = <5f5e1000>

        |   |- 64-bit

        |   |- linux,phandle = <2>
        |
        o memory@0
        | |- name = "memory"
        | |- device_type = "memory"
        | |- reg = <00000000 00000000 00000000 20000000>
        | |- linux,phandle = <3>
        |
        o chosen
          |- name = "chosen"
          |- bootargs = "root=/dev/sda2"

          |- linux,phandle = <4>
  
  This tree is almost a minimal tree. It pretty much contains the
  minimal set of required nodes and properties to boot a linux kernel;

  that is, some basic model information at the root, the CPUs, and the

  physical memory layout.  It also includes misc information passed
  through /chosen, like in this example, the platform type (mandatory)
  and the kernel command line arguments (optional).

  The /cpus/PowerPC,970@0/64-bit property is an example of a

  property without a value. All other properties have a value. The
  significance of the #address-cells and #size-cells properties will be
  explained in chapter IV which defines precisely the required nodes and
  properties and their content.
  
  
  3) Device tree "structure" block
  
  The structure of the device tree is a linearized tree structure. The
  "OF_DT_BEGIN_NODE" token starts a new node, and the "OF_DT_END_NODE"
  ends that node definition. Child nodes are simply defined before
  "OF_DT_END_NODE" (that is nodes within the node). A 'token' is a 32
  bit value. The tree has to be "finished" with a OF_DT_END token
  
  Here's the basic structure of a single node:
  
       * token OF_DT_BEGIN_NODE (that is 0x00000001)
       * for version 1 to 3, this is the node full path as a zero
         terminated string, starting with "/". For version 16 and later,
         this is the node unit name only (or an empty string for the
         root node)
       * [align gap to next 4 bytes boundary]
       * for each property:
          * token OF_DT_PROP (that is 0x00000003)

          * 32-bit value of property value size in bytes (or 0 if no
            value)
          * 32-bit value of offset in string block of property name

          * property value data if any
          * [align gap to next 4 bytes boundary]
       * [child nodes if any]
       * token OF_DT_END_NODE (that is 0x00000002)

  So the node content can be summarized as a start token, a full path,

  a list of properties, a list of child nodes, and an end token. Every

  child node is a full node structure itself as defined above.

  NOTE: The above definition requires that all property definitions for
  a particular node MUST precede any subnode definitions for that node.
  Although the structure would not be ambiguous if properties and
  subnodes were intermingled, the kernel parser requires that the
  properties come first (up until at least 2.6.22).  Any tools
  manipulating a flattened tree must take care to preserve this
  constraint.

  4) Device tree "strings" block

  
  In order to save space, property names, which are generally redundant,
  are stored separately in the "strings" block. This block is simply the
  whole bunch of zero terminated strings for all property names
  concatenated together. The device-tree property definitions in the
  structure block will contain offset values from the beginning of the
  strings block.
  
  
  III - Required content of the device tree
  =========================================
  
  WARNING: All "linux,*" properties defined in this document apply only
  to a flattened device-tree. If your platform uses a real
  implementation of Open Firmware or an implementation compatible with
  the Open Firmware client interface, those properties will be created
  by the trampoline code in the kernel's prom_init() file. For example,
  that's where you'll have to add code to detect your board model and

  set the platform number. However, when using the flattened device-tree

  entry point, there is no prom_init() pass, and thus you have to
  provide those properties yourself.
  
  
  1) Note about cells and address representation
  ----------------------------------------------
  
  The general rule is documented in the various Open Firmware

  documentations. If you choose to describe a bus with the device-tree

  and there exist an OF bus binding, then you should follow the
  specification. However, the kernel does not require every single
  device or bus to be described by the device tree.
  
  In general, the format of an address for a device is defined by the
  parent bus type, based on the #address-cells and #size-cells

  properties.  Note that the parent's parent definitions of #address-cells

  and #size-cells are not inherited so every node with children must specify

  them.  The kernel requires the root node to have those properties defining
  addresses format for devices directly mapped on the processor bus.

  
  Those 2 properties define 'cells' for representing an address and a

  size. A "cell" is a 32-bit number. For example, if both contain 2

  like the example tree given above, then an address and a size are both

  composed of 2 cells, and each is a 64-bit number (cells are

  concatenated and expected to be in big endian format). Another example
  is the way Apple firmware defines them, with 2 cells for an address
  and one cell for a size.  Most 32-bit implementations should define
  #address-cells and #size-cells to 1, which represents a 32-bit value.
  Some 32-bit processors allow for physical addresses greater than 32
  bits; these processors should define #address-cells as 2.
  
  "reg" properties are always a tuple of the type "address size" where
  the number of cells of address and size is specified by the bus
  #address-cells and #size-cells. When a bus supports various address
  spaces and other flags relative to a given address allocation (like
  prefetchable, etc...) those flags are usually added to the top level
  bits of the physical address. For example, a PCI physical address is
  made of 3 cells, the bottom two containing the actual address itself
  while the top cell contains address space indication, flags, and pci
  bus & device numbers.

  For buses that support dynamic allocation, it's the accepted practice

  to then not provide the address in "reg" (keep it 0) though while
  providing a flag indicating the address is dynamically allocated, and
  then, to provide a separate "assigned-addresses" property that
  contains the fully allocated addresses. See the PCI OF bindings for
  details.
  
  In general, a simple bus with no address space bits and no dynamic
  allocation is preferred if it reflects your hardware, as the existing
  kernel address parsing functions will work out of the box. If you
  define a bus type with a more complex address format, including things
  like address space bits, you'll have to add a bus translator to the
  prom_parse.c file of the recent kernels for your bus type.

  The "reg" property only defines addresses and sizes (if #size-cells is
  non-0) within a given bus. In order to translate addresses upward

  (that is into parent bus addresses, and possibly into CPU physical

  addresses), all buses must contain a "ranges" property. If the

  "ranges" property is missing at a given level, it's assumed that

  translation isn't possible, i.e., the registers are not visible on the
  parent bus.  The format of the "ranges" property for a bus is a list
  of:

  
  	bus address, parent bus address, size
  
  "bus address" is in the format of the bus this bus node is defining,
  that is, for a PCI bridge, it would be a PCI address. Thus, (bus
  address, size) defines a range of addresses for child devices. "parent
  bus address" is in the format of the parent bus of this bus. For
  example, for a PCI host controller, that would be a CPU address. For a
  PCI<->ISA bridge, that would be a PCI address. It defines the base
  address in the parent bus where the beginning of that range is mapped.

  For new 64-bit board support, I recommend either the 2/2 format or

  Apple's 2/1 format which is slightly more compact since sizes usually

  fit in a single 32-bit word.   New 32-bit board support should use a

  1/1 format, unless the processor supports physical addresses greater
  than 32-bits, in which case a 2/1 format is recommended.

  Alternatively, the "ranges" property may be empty, indicating that the
  registers are visible on the parent bus using an identity mapping
  translation.  In other words, the parent bus address space is the same
  as the child bus address space.

  
  2) Note about "compatible" properties
  -------------------------------------
  
  These properties are optional, but recommended in devices and the root
  node. The format of a "compatible" property is a list of concatenated
  zero terminated strings. They allow a device to express its
  compatibility with a family of similar devices, in some cases,
  allowing a single driver to match against several devices regardless
  of their actual names.
  
  3) Note about "name" properties
  -------------------------------
  
  While earlier users of Open Firmware like OldWorld macintoshes tended
  to use the actual device name for the "name" property, it's nowadays
  considered a good practice to use a name that is closer to the device

  class (often equal to device_type). For example, nowadays, Ethernet

  controllers are named "ethernet", an additional "model" property
  defining precisely the chip type/model, and "compatible" property
  defining the family in case a single driver can driver more than one
  of these chips. However, the kernel doesn't generally put any
  restriction on the "name" property; it is simply considered good
  practice to follow the standard and its evolutions as closely as
  possible.
  
  Note also that the new format version 16 makes the "name" property
  optional. If it's absent for a node, then the node's unit name is then
  used to reconstruct the name. That is, the part of the unit name
  before the "@" sign is used (or the entire unit name if no "@" sign
  is present).
  
  4) Note about node and property names and character set
  -------------------------------------------------------

  While Open Firmware provides more flexible usage of 8859-1, this

  specification enforces more strict rules. Nodes and properties should
  be comprised only of ASCII characters 'a' to 'z', '0' to
  '9', ',', '.', '_', '+', '#', '?', and '-'. Node names additionally
  allow uppercase characters 'A' to 'Z' (property names should be
  lowercase. The fact that vendors like Apple don't respect this rule is
  irrelevant here). Additionally, node and property names should always
  begin with a character in the range 'a' to 'z' (or 'A' to 'Z' for node
  names).
  
  The maximum number of characters for both nodes and property names
  is 31. In the case of node names, this is only the leftmost part of
  a unit name (the pure "name" property), it doesn't include the unit
  address which can extend beyond that limit.
  
  
  5) Required nodes and properties
  --------------------------------
    These are all that are currently required. However, it is strongly
    recommended that you expose PCI host bridges as documented in the

    PCI binding to Open Firmware, and your interrupt tree as documented

    in OF interrupt tree specification.
  
    a) The root node
  
    The root node requires some properties to be present:
  
      - model : this is your board name/model
      - #address-cells : address representation for "root" devices
      - #size-cells: the size representation for "root" devices

      - compatible : the board "family" generally finds its way here,
        for example, if you have 2 board models with a similar layout,
        that typically get driven by the same platform code in the

        kernel, you would specify the exact board model in the
        compatible property followed by an entry that represents the SoC
        model.

  
    The root node is also generally where you add additional properties
    specific to your board like the serial number if any, that sort of

    thing. It is recommended that if you add any "custom" property whose

    name may clash with standard defined ones, you prefix them with your
    vendor name and a comma.
  
    b) The /cpus node
  
    This node is the parent of all individual CPU nodes. It doesn't
    have any specific requirements, though it's generally good practice
    to have at least:
  
                 #address-cells = <00000001>
                 #size-cells    = <00000000>
  
    This defines that the "address" for a CPU is a single cell, and has
    no meaningful size. This is not necessary but the kernel will assume
    that format when reading the "reg" properties of a CPU node, see
    below
  
    c) The /cpus/* nodes
  
    So under /cpus, you are supposed to create a node for every CPU on
    the machine. There is no specific restriction on the name of the

    CPU, though it's common to call it <architecture>,<core>. For

    example, Apple uses PowerPC,G5 while IBM uses PowerPC,970FX.

    However, the Generic Names convention suggests that it would be
    better to simply use 'cpu' for each cpu node and use the compatible
    property to identify the specific cpu core.

  
    Required properties:
  
      - device_type : has to be "cpu"

      - reg : This is the physical CPU number, it's a single 32-bit cell

        and is also used as-is as the unit number for constructing the
        unit name in the full path. For example, with 2 CPUs, you would
        have the full path:
          /cpus/PowerPC,970FX@0
          /cpus/PowerPC,970FX@1
        (unit addresses do not require leading zeroes)

      - d-cache-block-size : one cell, L1 data cache block size in bytes (*)
      - i-cache-block-size : one cell, L1 instruction cache block size in

        bytes
      - d-cache-size : one cell, size of L1 data cache in bytes
      - i-cache-size : one cell, size of L1 instruction cache in bytes

  (*) The cache "block" size is the size on which the cache management
  instructions operate. Historically, this document used the cache
  "line" size here which is incorrect. The kernel will prefer the cache
  block size and will fallback to cache line size for backward
  compatibility.

    Recommended properties:
  
      - timebase-frequency : a cell indicating the frequency of the
        timebase in Hz. This is not directly used by the generic code,
        but you are welcome to copy/paste the pSeries code for setting
        the kernel timebase/decrementer calibration based on this
        value.
      - clock-frequency : a cell indicating the CPU core clock frequency

        in Hz. A new property will be defined for 64-bit values, but if

        your frequency is < 4Ghz, one cell is enough. Here as well as
        for the above, the common code doesn't use that property, but
        you are welcome to re-use the pSeries or Maple one. A future
        kernel version might provide a common function for this.

      - d-cache-line-size : one cell, L1 data cache line size in bytes
        if different from the block size
      - i-cache-line-size : one cell, L1 instruction cache line size in
        bytes if different from the block size

  
    You are welcome to add any property you find relevant to your board,
    like some information about the mechanism used to soft-reset the
    CPUs. For example, Apple puts the GPIO number for CPU soft reset
    lines in there as a "soft-reset" property since they start secondary
    CPUs by soft-resetting them.
  
  
    d) the /memory node(s)
  
    To define the physical memory layout of your board, you should
    create one or more memory node(s). You can either create a single
    node with all memory ranges in its reg property, or you can create
    several nodes, as you wish. The unit address (@ part) used for the
    full path is the address of the first range of memory defined by a
    given node. If you use a single memory node, this will typically be
    @0.
  
    Required properties:
  
      - device_type : has to be "memory"
      - reg : This property contains all the physical memory ranges of
        your board. It's a list of addresses/sizes concatenated
        together, with the number of cells of each defined by the
        #address-cells and #size-cells of the root node. For example,

        with both of these properties being 2 like in the example given

        earlier, a 970 based machine with 6Gb of RAM could typically
        have a "reg" property here that looks like:
  
        00000000 00000000 00000000 80000000
        00000001 00000000 00000001 00000000
  
        That is a range starting at 0 of 0x80000000 bytes and a range
        starting at 0x100000000 and of 0x100000000 bytes. You can see
        that there is no memory covering the IO hole between 2Gb and
        4Gb. Some vendors prefer splitting those ranges into smaller
        segments, but the kernel doesn't care.
  
    e) The /chosen node

    This node is a bit "special". Normally, that's where Open Firmware

    puts some variable environment information, like the arguments, or

    the default input/output devices.

  
    This specification makes a few of these mandatory, but also defines
    some linux-specific properties that would be normally constructed by
    the prom_init() trampoline when booting with an OF client interface,
    but that you have to provide yourself when using the flattened format.

    Recommended properties:
  
      - bootargs : This zero-terminated string is passed as the kernel
        command line
      - linux,stdout-path : This is the full path to your standard
        console device if any. Typically, if you have serial devices on
        your board, you may want to put the full path to the one set as
        the default console in the firmware here, for the kernel to pick

        it up as its own default console.

  
    Note that u-boot creates and fills in the chosen node for platforms
    that use it.

    (Note: a practice that is now obsolete was to include a property
    under /chosen called interrupt-controller which had a phandle value
    that pointed to the main interrupt controller)

    f) the /soc<SOCname> node

    This node is used to represent a system-on-a-chip (SoC) and must be
    present if the processor is a SoC. The top-level soc node contains
    information that is global to all devices on the SoC. The node name
    should contain a unit address for the SoC, which is the base address
    of the memory-mapped register set for the SoC. The name of an SoC

    node should start with "soc", and the remainder of the name should
    represent the part number for the soc.  For example, the MPC8540's
    soc node would be called "soc8540".
  
    Required properties:

      - ranges : Should be defined as specified in 1) to describe the

        translation of SoC addresses for memory mapped SoC registers.
      - bus-frequency: Contains the bus frequency for the SoC node.

        Typically, the value of this field is filled in by the boot

        loader.

      - compatible : Exact model of the SoC

  
    Recommended properties:
  
      - reg : This property defines the address and size of the
        memory-mapped registers that are used for the SOC node itself.
        It does not include the child device registers - these will be
        defined inside each child node.  The address specified in the
        "reg" property should match the unit address of the SOC node.
      - #address-cells : Address representation for "soc" devices.  The
        format of this field may vary depending on whether or not the
        device registers are memory mapped.  For memory mapped
        registers, this field represents the number of cells needed to
        represent the address of the registers.  For SOCs that do not
        use MMIO, a special address format should be defined that
        contains enough cells to represent the required information.
        See 1) above for more details on defining #address-cells.
      - #size-cells : Size representation for "soc" devices
      - #interrupt-cells : Defines the width of cells used to represent
         interrupts.  Typically this value is <2>, which includes a
         32-bit number that represents the interrupt number, and a
         32-bit number that represents the interrupt sense and level.
         This field is only needed if the SOC contains an interrupt
         controller.
  
    The SOC node may contain child nodes for each SOC device that the
    platform uses.  Nodes should not be created for devices which exist
    on the SOC but are not used by a particular platform. See chapter VI

    for more information on how to specify devices that are part of a SOC.

  
    Example SOC node for the MPC8540:
  
  	soc8540@e0000000 {
  		#address-cells = <1>;
  		#size-cells = <1>;
  		#interrupt-cells = <2>;
  		device_type = "soc";
  		ranges = <00000000 e0000000 00100000>
  		reg = <e0000000 00003000>;

  		bus-frequency = <0>;

  	}
  
  
  
  IV - "dtc", the device tree compiler
  ====================================
  
  
  dtc source code can be found at

  <http://git.jdl.com/gitweb/?p=dtc.git>

  
  WARNING: This version is still in early development stage; the
  resulting device-tree "blobs" have not yet been validated with the

  kernel. The current generated block lacks a useful reserve map (it will

  be fixed to generate an empty one, it's up to the bootloader to fill
  it up) among others. The error handling needs work, bugs are lurking,
  etc...
  
  dtc basically takes a device-tree in a given format and outputs a
  device-tree in another format. The currently supported formats are:
  
    Input formats:
    -------------
  
       - "dtb": "blob" format, that is a flattened device-tree block
         with
          header all in a binary blob.
       - "dts": "source" format. This is a text file containing a
         "source" for a device-tree. The format is defined later in this
          chapter.
       - "fs" format. This is a representation equivalent to the
          output of /proc/device-tree, that is nodes are directories and
  	properties are files
  
   Output formats:
   ---------------
  
       - "dtb": "blob" format
       - "dts": "source" format
       - "asm": assembly language file. This is a file that can be
         sourced by gas to generate a device-tree "blob". That file can
         then simply be added to your Makefile. Additionally, the

         assembly file exports some symbols that can be used.

  
  
  The syntax of the dtc tool is
  
      dtc [-I <input-format>] [-O <output-format>]
          [-o output-filename] [-V output_version] input_filename

  The "output_version" defines what version of the "blob" format will be

  generated. Supported versions are 1,2,3 and 16. The default is
  currently version 3 but that may change in the future to version 16.
  
  Additionally, dtc performs various sanity checks on the tree, like the

  uniqueness of linux, phandle properties, validity of strings, etc...

  
  The format of the .dts "source" file is "C" like, supports C and C++

  style comments.

  
  / {
  }
  
  The above is the "device-tree" definition. It's the only statement
  supported currently at the toplevel.
  
  / {
    property1 = "string_value";	/* define a property containing a 0
                                   * terminated string
  				 */
  
    property2 = <1234abcd>;	/* define a property containing a

                                   * numerical 32-bit value (hexadecimal)

  				 */
  
    property3 = <12345678 12345678 deadbeef>;
                                  /* define a property containing 3

                                   * numerical 32-bit values (cells) in

                                   * hexadecimal
  				 */
    property4 = [0a 0b 0c 0d de ea ad be ef];
                                  /* define a property whose content is
                                   * an arbitrary array of bytes
                                   */

    childnode@address {	/* define a child node named "childnode"

                                   * whose unit name is "childnode at
  				 * address"
                                   */
  
      childprop = "hello
  ";      /* define a property "childprop" of
                                   * childnode (in this case, a string)
                                   */
    };
  };
  
  Nodes can contain other nodes etc... thus defining the hierarchical
  structure of the tree.
  
  Strings support common escape sequences from C: "
  ", "\t", "\r",
  "\(octal value)", "\x(hex value)".
  
  It is also suggested that you pipe your source file through cpp (gcc
  preprocessor) so you can use #include's, #define for constants, etc...
  
  Finally, various options are planned but not yet implemented, like
  automatic generation of phandles, labels (exported to the asm file so
  you can point to a property content and change it easily from whatever
  you link the device-tree with), label or path instead of numeric value
  in some cells to "point" to a node (replaced by a phandle at compile
  time), export of reserve map address to the asm file, ability to
  specify reserve map content at compile time, etc...
  
  We may provide a .h include file with common definitions of that
  proves useful for some properties (like building PCI properties or
  interrupt maps) though it may be better to add a notion of struct
  definitions to the compiler...
  
  
  V - Recommendations for a bootloader
  ====================================
  
  
  Here are some various ideas/recommendations that have been proposed
  while all this has been defined and implemented.
  
    - The bootloader may want to be able to use the device-tree itself
      and may want to manipulate it (to add/edit some properties,
      like physical memory size or kernel arguments). At this point, 2
      choices can be made. Either the bootloader works directly on the
      flattened format, or the bootloader has its own internal tree
      representation with pointers (similar to the kernel one) and
      re-flattens the tree when booting the kernel. The former is a bit
      more difficult to edit/modify, the later requires probably a bit
      more code to handle the tree structure. Note that the structure
      format has been designed so it's relatively easy to "insert"
      properties or nodes or delete them by just memmoving things
      around. It contains no internal offsets or pointers for this
      purpose.

    - An example of code for iterating nodes & retrieving properties

      directly from the flattened tree format can be found in the kernel

      file drivers/of/fdt.c.  Look at the of_scan_flat_dt() function,

      its usage in early_init_devtree(), and the corresponding various

      early_init_dt_scan_*() callbacks. That code can be re-used in a
      GPL bootloader, and as the author of that code, I would be happy

      to discuss possible free licensing to any vendor who wishes to

      integrate all or part of this code into a non-GPL bootloader.

      (reference needed; who is 'I' here? ---gcl Jan 31, 2011)

  
  
  
  VI - System-on-a-chip devices and nodes
  =======================================
  
  Many companies are now starting to develop system-on-a-chip

  processors, where the processor core (CPU) and many peripheral devices

  exist on a single piece of silicon.  For these SOCs, an SOC node
  should be used that defines child nodes for the devices that make
  up the SOC. While platforms are not required to use this model in
  order to boot the kernel, it is highly encouraged that all SOC
  implementations define as complete a flat-device-tree as possible to
  describe the devices on the SOC.  This will allow for the
  genericization of much of the kernel code.
  
  
  1) Defining child nodes of an SOC
  ---------------------------------
  
  Each device that is part of an SOC may have its own node entry inside
  the SOC node.  For each device that is included in the SOC, the unit
  address property represents the address offset for this device's
  memory-mapped registers in the parent's address space.  The parent's
  address space is defined by the "ranges" property in the top-level soc
  node. The "reg" property for each node that exists directly under the
  SOC node should contain the address mapping from the child address space
  to the parent SOC address space and the size of the device's
  memory-mapped register file.
  
  For many devices that may exist inside an SOC, there are predefined
  specifications for the format of the device tree node.  All SOC child
  nodes should follow these specifications, except where noted in this
  document.
  
  See appendix A for an example partial SOC node definition for the
  MPC8540.

  2) Representing devices without a current OF specification

  ----------------------------------------------------------

  Currently, there are many devices on SoCs that do not have a standard
  representation defined as part of the Open Firmware specifications,
  mainly because the boards that contain these SoCs are not currently
  booted using Open Firmware.  Binding documentation for new devices
  should be added to the Documentation/devicetree/bindings directory.
  That directory will expand as device tree support is added to more and
  more SoCs.

  VII - Specifying interrupt information for devices

  ===================================================

  The device tree represents the buses and devices of a hardware

  system in a form similar to the physical bus topology of the
  hardware.
  
  In addition, a logical 'interrupt tree' exists which represents the
  hierarchy and routing of interrupts in the hardware.
  
  The interrupt tree model is fully described in the
  document "Open Firmware Recommended Practice: Interrupt
  Mapping Version 0.9".  The document is available at:
  <http://playground.sun.com/1275/practice>.
  
  1) interrupts property
  ----------------------
  
  Devices that generate interrupts to a single interrupt controller
  should use the conventional OF representation described in the
  OF interrupt mapping documentation.
  
  Each device which generates interrupts must have an 'interrupt'
  property.  The interrupt property value is an arbitrary number of
  of 'interrupt specifier' values which describe the interrupt or
  interrupts for the device.
  
  The encoding of an interrupt specifier is determined by the
  interrupt domain in which the device is located in the
  interrupt tree.  The root of an interrupt domain specifies in
  its #interrupt-cells property the number of 32-bit cells
  required to encode an interrupt specifier.  See the OF interrupt
  mapping documentation for a detailed description of domains.
  
  For example, the binding for the OpenPIC interrupt controller
  specifies  an #interrupt-cells value of 2 to encode the interrupt
  number and level/sense information. All interrupt children in an
  OpenPIC interrupt domain use 2 cells per interrupt in their interrupts
  property.
  
  The PCI bus binding specifies a #interrupt-cell value of 1 to encode
  which interrupt pin (INTA,INTB,INTC,INTD) is used.
  
  2) interrupt-parent property
  ----------------------------
  
  The interrupt-parent property is specified to define an explicit
  link between a device node and its interrupt parent in
  the interrupt tree.  The value of interrupt-parent is the
  phandle of the parent node.

  If the interrupt-parent property is not defined for a node, its

  interrupt parent is assumed to be an ancestor in the node's
  _device tree_ hierarchy.
  
  3) OpenPIC Interrupt Controllers
  --------------------------------
  
  OpenPIC interrupt controllers require 2 cells to encode
  interrupt information.  The first cell defines the interrupt
  number.  The second cell defines the sense and level
  information.
  
  Sense and level information should be encoded as follows:
  
  	0 = low to high edge sensitive type enabled
  	1 = active low level sensitive type enabled
  	2 = active high level sensitive type enabled
  	3 = high to low edge sensitive type enabled
  
  4) ISA Interrupt Controllers
  ----------------------------
  
  ISA PIC interrupt controllers require 2 cells to encode
  interrupt information.  The first cell defines the interrupt
  number.  The second cell defines the sense and level
  information.
  
  ISA PIC interrupt controllers should adhere to the ISA PIC
  encodings listed below:
  
  	0 =  active low level sensitive type enabled
  	1 =  active high level sensitive type enabled
  	2 =  high to low edge sensitive type enabled
  	3 =  low to high edge sensitive type enabled

  VIII - Specifying Device Power Management Information (sleep property)

  ===================================================================
  
  Devices on SOCs often have mechanisms for placing devices into low-power
  states that are decoupled from the devices' own register blocks.  Sometimes,
  this information is more complicated than a cell-index property can
  reasonably describe.  Thus, each device controlled in such a manner
  may contain a "sleep" property which describes these connections.
  
  The sleep property consists of one or more sleep resources, each of
  which consists of a phandle to a sleep controller, followed by a
  controller-specific sleep specifier of zero or more cells.
  
  The semantics of what type of low power modes are possible are defined
  by the sleep controller.  Some examples of the types of low power modes
  that may be supported are:
  
   - Dynamic: The device may be disabled or enabled at any time.
   - System Suspend: The device may request to be disabled or remain
     awake during system suspend, but will not be disabled until then.
   - Permanent: The device is disabled permanently (until the next hard
     reset).
  
  Some devices may share a clock domain with each other, such that they should
  only be suspended when none of the devices are in use.  Where reasonable,
  such nodes should be placed on a virtual bus, where the bus has the sleep
  property.  If the clock domain is shared among devices that cannot be
  reasonably grouped in this manner, then create a virtual sleep controller
  (similar to an interrupt nexus, except that defining a standardized
  sleep-map should wait until its necessity is demonstrated).

  Appendix A - Sample SOC node for MPC8540
  ========================================

  	soc@e0000000 {

  		#address-cells = <1>;
  		#size-cells = <1>;

  		compatible = "fsl,mpc8540-ccsr", "simple-bus";

  		device_type = "soc";

  		ranges = <0x00000000 0xe0000000 0x00100000>

  		bus-frequency = <0>;

  		interrupt-parent = <&pic>;

  		ethernet@24000 {

  			#address-cells = <1>;
  			#size-cells = <1>;

  			device_type = "network";
  			model = "TSEC";

  			compatible = "gianfar", "simple-bus";

  			reg = <0x24000 0x1000>;
  			local-mac-address = [ 00 E0 0C 00 73 00 ];
  			interrupts = <29 2 30 2 34 2>;
  			phy-handle = <&phy0>;

  			sleep = <&pmc 00000080>;
  			ranges;
  
  			mdio@24520 {

  				reg = <0x24520 0x20>;

  				compatible = "fsl,gianfar-mdio";

  				phy0: ethernet-phy@0 {
  					interrupts = <5 1>;

  					reg = <0>;
  					device_type = "ethernet-phy";
  				};

  				phy1: ethernet-phy@1 {
  					interrupts = <5 1>;

  					reg = <1>;
  					device_type = "ethernet-phy";
  				};

  				phy3: ethernet-phy@3 {
  					interrupts = <7 1>;

  					reg = <3>;
  					device_type = "ethernet-phy";
  				};
  			};

  		};
  
  		ethernet@25000 {

  			device_type = "network";
  			model = "TSEC";
  			compatible = "gianfar";

  			reg = <0x25000 0x1000>;
  			local-mac-address = [ 00 E0 0C 00 73 01 ];
  			interrupts = <13 2 14 2 18 2>;
  			phy-handle = <&phy1>;

  			sleep = <&pmc 00000040>;

  		};
  
  		ethernet@26000 {

  			device_type = "network";
  			model = "FEC";
  			compatible = "gianfar";

  			reg = <0x26000 0x1000>;
  			local-mac-address = [ 00 E0 0C 00 73 02 ];
  			interrupts = <41 2>;
  			phy-handle = <&phy3>;

  			sleep = <&pmc 00000020>;

  		};
  
  		serial@4500 {

  			#address-cells = <1>;
  			#size-cells = <1>;
  			compatible = "fsl,mpc8540-duart", "simple-bus";
  			sleep = <&pmc 00000002>;
  			ranges;
  
  			serial@4500 {
  				device_type = "serial";
  				compatible = "ns16550";

  				reg = <0x4500 0x100>;

  				clock-frequency = <0>;

  				interrupts = <42 2>;

  			};
  
  			serial@4600 {
  				device_type = "serial";
  				compatible = "ns16550";

  				reg = <0x4600 0x100>;

  				clock-frequency = <0>;

  				interrupts = <42 2>;

  			};

  		};

  		pic: pic@40000 {

  			interrupt-controller;
  			#address-cells = <0>;

  			#interrupt-cells = <2>;
  			reg = <0x40000 0x40000>;

  			compatible = "chrp,open-pic";
  			device_type = "open-pic";

  		};
  
  		i2c@3000 {

  			interrupts = <43 2>;
  			reg = <0x3000 0x100>;

  			compatible  = "fsl-i2c";
  			dfsrr;

  			sleep = <&pmc 00000004>;

  		};

  		pmc: power@e0070 {
  			compatible = "fsl,mpc8540-pmc", "fsl,mpc8548-pmc";

  			reg = <0xe0070 0x20>;

  		};

  	};