linux/Documentation/devicetree/booting-without-of.txt
<<
>>
Prefs
   1           Booting the Linux/ppc kernel without Open Firmware
   2           --------------------------------------------------
   3
   4(c) 2005 Benjamin Herrenschmidt <benh at kernel.crashing.org>,
   5    IBM Corp.
   6(c) 2005 Becky Bruce <becky.bruce at freescale.com>,
   7    Freescale Semiconductor, FSL SOC and 32-bit additions
   8(c) 2006 MontaVista Software, Inc.
   9    Flash chip node definition
  10
  11Table of Contents
  12=================
  13
  14  I - Introduction
  15    1) Entry point for arch/arm
  16    2) Entry point for arch/powerpc
  17    3) Entry point for arch/x86
  18
  19  II - The DT block format
  20    1) Header
  21    2) Device tree generalities
  22    3) Device tree "structure" block
  23    4) Device tree "strings" block
  24
  25  III - Required content of the device tree
  26    1) Note about cells and address representation
  27    2) Note about "compatible" properties
  28    3) Note about "name" properties
  29    4) Note about node and property names and character set
  30    5) Required nodes and properties
  31      a) The root node
  32      b) The /cpus node
  33      c) The /cpus/* nodes
  34      d) the /memory node(s)
  35      e) The /chosen node
  36      f) the /soc<SOCname> node
  37
  38  IV - "dtc", the device tree compiler
  39
  40  V - Recommendations for a bootloader
  41
  42  VI - System-on-a-chip devices and nodes
  43    1) Defining child nodes of an SOC
  44    2) Representing devices without a current OF specification
  45
  46  VII - Specifying interrupt information for devices
  47    1) interrupts property
  48    2) interrupt-parent property
  49    3) OpenPIC Interrupt Controllers
  50    4) ISA Interrupt Controllers
  51
  52  VIII - Specifying device power management information (sleep property)
  53
  54  Appendix A - Sample SOC node for MPC8540
  55
  56
  57Revision Information
  58====================
  59
  60   May 18, 2005: Rev 0.1 - Initial draft, no chapter III yet.
  61
  62   May 19, 2005: Rev 0.2 - Add chapter III and bits & pieces here or
  63                           clarifies the fact that a lot of things are
  64                           optional, the kernel only requires a very
  65                           small device tree, though it is encouraged
  66                           to provide an as complete one as possible.
  67
  68   May 24, 2005: Rev 0.3 - Precise that DT block has to be in RAM
  69                         - Misc fixes
  70                         - Define version 3 and new format version 16
  71                           for the DT block (version 16 needs kernel
  72                           patches, will be fwd separately).
  73                           String block now has a size, and full path
  74                           is replaced by unit name for more
  75                           compactness.
  76                           linux,phandle is made optional, only nodes
  77                           that are referenced by other nodes need it.
  78                           "name" property is now automatically
  79                           deduced from the unit name
  80
  81   June 1, 2005: Rev 0.4 - Correct confusion between OF_DT_END and
  82                           OF_DT_END_NODE in structure definition.
  83                         - Change version 16 format to always align
  84                           property data to 4 bytes. Since tokens are
  85                           already aligned, that means no specific
  86                           required alignment between property size
  87                           and property data. The old style variable
  88                           alignment would make it impossible to do
  89                           "simple" insertion of properties using
  90                           memmove (thanks Milton for
  91                           noticing). Updated kernel patch as well
  92                         - Correct a few more alignment constraints
  93                         - Add a chapter about the device-tree
  94                           compiler and the textural representation of
  95                           the tree that can be "compiled" by dtc.
  96
  97   November 21, 2005: Rev 0.5
  98                         - Additions/generalizations for 32-bit
  99                         - Changed to reflect the new arch/powerpc
 100                           structure
 101                         - Added chapter VI
 102
 103
 104 ToDo:
 105        - Add some definitions of interrupt tree (simple/complex)
 106        - Add some definitions for PCI host bridges
 107        - Add some common address format examples
 108        - Add definitions for standard properties and "compatible"
 109          names for cells that are not already defined by the existing
 110          OF spec.
 111        - Compare FSL SOC use of PCI to standard and make sure no new
 112          node definition required.
 113        - Add more information about node definitions for SOC devices
 114          that currently have no standard, like the FSL CPM.
 115
 116
 117I - Introduction
 118================
 119
 120During the development of the Linux/ppc64 kernel, and more
 121specifically, the addition of new platform types outside of the old
 122IBM pSeries/iSeries pair, it was decided to enforce some strict rules
 123regarding the kernel entry and bootloader <-> kernel interfaces, in
 124order to avoid the degeneration that had become the ppc32 kernel entry
 125point and the way a new platform should be added to the kernel. The
 126legacy iSeries platform breaks those rules as it predates this scheme,
 127but no new board support will be accepted in the main tree that
 128doesn't follow them properly.  In addition, since the advent of the
 129arch/powerpc merged architecture for ppc32 and ppc64, new 32-bit
 130platforms and 32-bit platforms which move into arch/powerpc will be
 131required to use these rules as well.
 132
 133The main requirement that will be defined in more detail below is
 134the presence of a device-tree whose format is defined after Open
 135Firmware specification. However, in order to make life easier
 136to embedded board vendors, the kernel doesn't require the device-tree
 137to represent every device in the system and only requires some nodes
 138and properties to be present. This will be described in detail in
 139section III, but, for example, the kernel does not require you to
 140create a node for every PCI device in the system. It is a requirement
 141to have a node for PCI host bridges in order to provide interrupt
 142routing information and memory/IO ranges, among others. It is also
 143recommended to define nodes for on chip devices and other buses that
 144don't specifically fit in an existing OF specification. This creates a
 145great flexibility in the way the kernel can then probe those and match
 146drivers to device, without having to hard code all sorts of tables. It
 147also makes it more flexible for board vendors to do minor hardware
 148upgrades without significantly impacting the kernel code or cluttering
 149it with special cases.
 150
 151
 1521) Entry point for arch/arm
 153---------------------------
 154
 155   There is one single entry point to the kernel, at the start
 156   of the kernel image. That entry point supports two calling
 157   conventions.  A summary of the interface is described here.  A full
 158   description of the boot requirements is documented in
 159   Documentation/arm/Booting
 160
 161        a) ATAGS interface.  Minimal information is passed from firmware
 162        to the kernel with a tagged list of predefined parameters.
 163
 164                r0 : 0
 165
 166                r1 : Machine type number
 167
 168                r2 : Physical address of tagged list in system RAM
 169
 170        b) Entry with a flattened device-tree block.  Firmware loads the
 171        physical address of the flattened device tree block (dtb) into r2,
 172        r1 is not used, but it is considered good practice to use a valid
 173        machine number as described in Documentation/arm/Booting.
 174
 175                r0 : 0
 176
 177                r1 : Valid machine type number.  When using a device tree,
 178                a single machine type number will often be assigned to
 179                represent a class or family of SoCs.
 180
 181                r2 : physical pointer to the device-tree block
 182                (defined in chapter II) in RAM.  Device tree can be located
 183                anywhere in system RAM, but it should be aligned on a 64 bit
 184                boundary.
 185
 186   The kernel will differentiate between ATAGS and device tree booting by
 187   reading the memory pointed to by r2 and looking for either the flattened
 188   device tree block magic value (0xd00dfeed) or the ATAG_CORE value at
 189   offset 0x4 from r2 (0x54410001).
 190
 1912) Entry point for arch/powerpc
 192-------------------------------
 193
 194   There is one single entry point to the kernel, at the start
 195   of the kernel image. That entry point supports two calling
 196   conventions:
 197
 198        a) Boot from Open Firmware. If your firmware is compatible
 199        with Open Firmware (IEEE 1275) or provides an OF compatible
 200        client interface API (support for "interpret" callback of
 201        forth words isn't required), you can enter the kernel with:
 202
 203              r5 : OF callback pointer as defined by IEEE 1275
 204              bindings to powerpc. Only the 32-bit client interface
 205              is currently supported
 206
 207              r3, r4 : address & length of an initrd if any or 0
 208
 209              The MMU is either on or off; the kernel will run the
 210              trampoline located in arch/powerpc/kernel/prom_init.c to
 211              extract the device-tree and other information from open
 212              firmware and build a flattened device-tree as described
 213              in b). prom_init() will then re-enter the kernel using
 214              the second method. This trampoline code runs in the
 215              context of the firmware, which is supposed to handle all
 216              exceptions during that time.
 217
 218        b) Direct entry with a flattened device-tree block. This entry
 219        point is called by a) after the OF trampoline and can also be
 220        called directly by a bootloader that does not support the Open
 221        Firmware client interface. It is also used by "kexec" to
 222        implement "hot" booting of a new kernel from a previous
 223        running one. This method is what I will describe in more
 224        details in this document, as method a) is simply standard Open
 225        Firmware, and thus should be implemented according to the
 226        various standard documents defining it and its binding to the
 227        PowerPC platform. The entry point definition then becomes:
 228
 229                r3 : physical pointer to the device-tree block
 230                (defined in chapter II) in RAM
 231
 232                r4 : physical pointer to the kernel itself. This is
 233                used by the assembly code to properly disable the MMU
 234                in case you are entering the kernel with MMU enabled
 235                and a non-1:1 mapping.
 236
 237                r5 : NULL (as to differentiate with method a)
 238
 239        Note about SMP entry: Either your firmware puts your other
 240        CPUs in some sleep loop or spin loop in ROM where you can get
 241        them out via a soft reset or some other means, in which case
 242        you don't need to care, or you'll have to enter the kernel
 243        with all CPUs. The way to do that with method b) will be
 244        described in a later revision of this document.
 245
 246   Board supports (platforms) are not exclusive config options. An
 247   arbitrary set of board supports can be built in a single kernel
 248   image. The kernel will "know" what set of functions to use for a
 249   given platform based on the content of the device-tree. Thus, you
 250   should:
 251
 252        a) add your platform support as a _boolean_ option in
 253        arch/powerpc/Kconfig, following the example of PPC_PSERIES,
 254        PPC_PMAC and PPC_MAPLE. The later is probably a good
 255        example of a board support to start from.
 256
 257        b) create your main platform file as
 258        "arch/powerpc/platforms/myplatform/myboard_setup.c" and add it
 259        to the Makefile under the condition of your CONFIG_
 260        option. This file will define a structure of type "ppc_md"
 261        containing the various callbacks that the generic code will
 262        use to get to your platform specific code
 263
 264  A kernel image may support multiple platforms, but only if the
 265  platforms feature the same core architecture.  A single kernel build
 266  cannot support both configurations with Book E and configurations
 267  with classic Powerpc architectures.
 268
 2693) Entry point for arch/x86
 270-------------------------------
 271
 272  There is one single 32bit entry point to the kernel at code32_start,
 273  the decompressor (the real mode entry point goes to the same  32bit
 274  entry point once it switched into protected mode). That entry point
 275  supports one calling convention which is documented in
 276  Documentation/x86/boot.txt
 277  The physical pointer to the device-tree block (defined in chapter II)
 278  is passed via setup_data which requires at least boot protocol 2.09.
 279  The type filed is defined as
 280
 281  #define SETUP_DTB                      2
 282
 283  This device-tree is used as an extension to the "boot page". As such it
 284  does not parse / consider data which is already covered by the boot
 285  page. This includes memory size, reserved ranges, command line arguments
 286  or initrd address. It simply holds information which can not be retrieved
 287  otherwise like interrupt routing or a list of devices behind an I2C bus.
 288
 289II - The DT block format
 290========================
 291
 292
 293This chapter defines the actual format of the flattened device-tree
 294passed to the kernel. The actual content of it and kernel requirements
 295are described later. You can find example of code manipulating that
 296format in various places, including arch/powerpc/kernel/prom_init.c
 297which will generate a flattened device-tree from the Open Firmware
 298representation, or the fs2dt utility which is part of the kexec tools
 299which will generate one from a filesystem representation. It is
 300expected that a bootloader like uboot provides a bit more support,
 301that will be discussed later as well.
 302
 303Note: The block has to be in main memory. It has to be accessible in
 304both real mode and virtual mode with no mapping other than main
 305memory. If you are writing a simple flash bootloader, it should copy
 306the block to RAM before passing it to the kernel.
 307
 308
 3091) Header
 310---------
 311
 312   The kernel is passed the physical address pointing to an area of memory
 313   that is roughly described in include/linux/of_fdt.h by the structure
 314   boot_param_header:
 315
 316struct boot_param_header {
 317        u32     magic;                  /* magic word OF_DT_HEADER */
 318        u32     totalsize;              /* total size of DT block */
 319        u32     off_dt_struct;          /* offset to structure */
 320        u32     off_dt_strings;         /* offset to strings */
 321        u32     off_mem_rsvmap;         /* offset to memory reserve map
 322                                           */
 323        u32     version;                /* format version */
 324        u32     last_comp_version;      /* last compatible version */
 325
 326        /* version 2 fields below */
 327        u32     boot_cpuid_phys;        /* Which physical CPU id we're
 328                                           booting on */
 329        /* version 3 fields below */
 330        u32     size_dt_strings;        /* size of the strings block */
 331
 332        /* version 17 fields below */
 333        u32     size_dt_struct;         /* size of the DT structure block */
 334};
 335
 336   Along with the constants:
 337
 338/* Definitions used by the flattened device tree */
 339#define OF_DT_HEADER            0xd00dfeed      /* 4: version,
 340                                                   4: total size */
 341#define OF_DT_BEGIN_NODE        0x1             /* Start node: full name
 342                                                   */
 343#define OF_DT_END_NODE          0x2             /* End node */
 344#define OF_DT_PROP              0x3             /* Property: name off,
 345                                                   size, content */
 346#define OF_DT_END               0x9
 347
 348   All values in this header are in big endian format, the various
 349   fields in this header are defined more precisely below. All
 350   "offset" values are in bytes from the start of the header; that is
 351   from the physical base address of the device tree block.
 352
 353   - magic
 354
 355     This is a magic value that "marks" the beginning of the
 356     device-tree block header. It contains the value 0xd00dfeed and is
 357     defined by the constant OF_DT_HEADER
 358
 359   - totalsize
 360
 361     This is the total size of the DT block including the header. The
 362     "DT" block should enclose all data structures defined in this
 363     chapter (who are pointed to by offsets in this header). That is,
 364     the device-tree structure, strings, and the memory reserve map.
 365
 366   - off_dt_struct
 367
 368     This is an offset from the beginning of the header to the start
 369     of the "structure" part the device tree. (see 2) device tree)
 370
 371   - off_dt_strings
 372
 373     This is an offset from the beginning of the header to the start
 374     of the "strings" part of the device-tree
 375
 376   - off_mem_rsvmap
 377
 378     This is an offset from the beginning of the header to the start
 379     of the reserved memory map. This map is a list of pairs of 64-
 380     bit integers. Each pair is a physical address and a size. The
 381     list is terminated by an entry of size 0. This map provides the
 382     kernel with a list of physical memory areas that are "reserved"
 383     and thus not to be used for memory allocations, especially during
 384     early initialization. The kernel needs to allocate memory during
 385     boot for things like un-flattening the device-tree, allocating an
 386     MMU hash table, etc... Those allocations must be done in such a
 387     way to avoid overriding critical things like, on Open Firmware
 388     capable machines, the RTAS instance, or on some pSeries, the TCE
 389     tables used for the iommu. Typically, the reserve map should
 390     contain _at least_ this DT block itself (header,total_size). If
 391     you are passing an initrd to the kernel, you should reserve it as
 392     well. You do not need to reserve the kernel image itself. The map
 393     should be 64-bit aligned.
 394
 395   - version
 396
 397     This is the version of this structure. Version 1 stops
 398     here. Version 2 adds an additional field boot_cpuid_phys.
 399     Version 3 adds the size of the strings block, allowing the kernel
 400     to reallocate it easily at boot and free up the unused flattened
 401     structure after expansion. Version 16 introduces a new more
 402     "compact" format for the tree itself that is however not backward
 403     compatible. Version 17 adds an additional field, size_dt_struct,
 404     allowing it to be reallocated or moved more easily (this is
 405     particularly useful for bootloaders which need to make
 406     adjustments to a device tree based on probed information). You
 407     should always generate a structure of the highest version defined
 408     at the time of your implementation. Currently that is version 17,
 409     unless you explicitly aim at being backward compatible.
 410
 411   - last_comp_version
 412
 413     Last compatible version. This indicates down to what version of
 414     the DT block you are backward compatible. For example, version 2
 415     is backward compatible with version 1 (that is, a kernel build
 416     for version 1 will be able to boot with a version 2 format). You
 417     should put a 1 in this field if you generate a device tree of
 418     version 1 to 3, or 16 if you generate a tree of version 16 or 17
 419     using the new unit name format.
 420
 421   - boot_cpuid_phys
 422
 423     This field only exist on version 2 headers. It indicate which
 424     physical CPU ID is calling the kernel entry point. This is used,
 425     among others, by kexec. If you are on an SMP system, this value
 426     should match the content of the "reg" property of the CPU node in
 427     the device-tree corresponding to the CPU calling the kernel entry
 428     point (see further chapters for more information on the required
 429     device-tree contents)
 430
 431   - size_dt_strings
 432
 433     This field only exists on version 3 and later headers.  It
 434     gives the size of the "strings" section of the device tree (which
 435     starts at the offset given by off_dt_strings).
 436
 437   - size_dt_struct
 438
 439     This field only exists on version 17 and later headers.  It gives
 440     the size of the "structure" section of the device tree (which
 441     starts at the offset given by off_dt_struct).
 442
 443   So the typical layout of a DT block (though the various parts don't
 444   need to be in that order) looks like this (addresses go from top to
 445   bottom):
 446
 447
 448             ------------------------------
 449     base -> |  struct boot_param_header  |
 450             ------------------------------
 451             |      (alignment gap) (*)   |
 452             ------------------------------
 453             |      memory reserve map    |
 454             ------------------------------
 455             |      (alignment gap)       |
 456             ------------------------------
 457             |                            |
 458             |    device-tree structure   |
 459             |                            |
 460             ------------------------------
 461             |      (alignment gap)       |
 462             ------------------------------
 463             |                            |
 464             |     device-tree strings    |
 465             |                            |
 466      -----> ------------------------------
 467      |
 468      |
 469      --- (base + totalsize)
 470
 471  (*) The alignment gaps are not necessarily present; their presence
 472      and size are dependent on the various alignment requirements of
 473      the individual data blocks.
 474
 475
 4762) Device tree generalities
 477---------------------------
 478
 479This device-tree itself is separated in two different blocks, a
 480structure block and a strings block. Both need to be aligned to a 4
 481byte boundary.
 482
 483First, let's quickly describe the device-tree concept before detailing
 484the storage format. This chapter does _not_ describe the detail of the
 485required types of nodes & properties for the kernel, this is done
 486later in chapter III.
 487
 488The device-tree layout is strongly inherited from the definition of
 489the Open Firmware IEEE 1275 device-tree. It's basically a tree of
 490nodes, each node having two or more named properties. A property can
 491have a value or not.
 492
 493It is a tree, so each node has one and only one parent except for the
 494root node who has no parent.
 495
 496A node has 2 names. The actual node name is generally contained in a
 497property of type "name" in the node property list whose value is a
 498zero terminated string and is mandatory for version 1 to 3 of the
 499format definition (as it is in Open Firmware). Version 16 makes it
 500optional as it can generate it from the unit name defined below.
 501
 502There is also a "unit name" that is used to differentiate nodes with
 503the same name at the same level, it is usually made of the node
 504names, the "@" sign, and a "unit address", which definition is
 505specific to the bus type the node sits on.
 506
 507The unit name doesn't exist as a property per-se but is included in
 508the device-tree structure. It is typically used to represent "path" in
 509the device-tree. More details about the actual format of these will be
 510below.
 511
 512The kernel generic code does not make any formal use of the
 513unit address (though some board support code may do) so the only real
 514requirement here for the unit address is to ensure uniqueness of
 515the node unit name at a given level of the tree. Nodes with no notion
 516of address and no possible sibling of the same name (like /memory or
 517/cpus) may omit the unit address in the context of this specification,
 518or use the "@0" default unit address. The unit name is used to define
 519a node "full path", which is the concatenation of all parent node
 520unit names separated with "/".
 521
 522The root node doesn't have a defined name, and isn't required to have
 523a name property either if you are using version 3 or earlier of the
 524format. It also has no unit address (no @ symbol followed by a unit
 525address). The root node unit name is thus an empty string. The full
 526path to the root node is "/".
 527
 528Every node which actually represents an actual device (that is, a node
 529which isn't only a virtual "container" for more nodes, like "/cpus"
 530is) is also required to have a "compatible" property indicating the
 531specific hardware and an optional list of devices it is fully
 532backwards compatible with.
 533
 534Finally, every node that can be referenced from a property in another
 535node is required to have either a "phandle" or a "linux,phandle"
 536property. Real Open Firmware implementations provide a unique
 537"phandle" value for every node that the "prom_init()" trampoline code
 538turns into "linux,phandle" properties. However, this is made optional
 539if the flattened device tree is used directly. An example of a node
 540referencing another node via "phandle" is when laying out the
 541interrupt tree which will be described in a further version of this
 542document.
 543
 544The "phandle" property is a 32-bit value that uniquely
 545identifies a node. You are free to use whatever values or system of
 546values, internal pointers, or whatever to generate these, the only
 547requirement is that every node for which you provide that property has
 548a unique value for it.
 549
 550Here is an example of a simple device-tree. In this example, an "o"
 551designates a node followed by the node unit name. Properties are
 552presented with their name followed by their content. "content"
 553represents an ASCII string (zero terminated) value, while <content>
 554represents a 32-bit value, specified in decimal or hexadecimal (the
 555latter prefixed 0x). The various nodes in this example will be
 556discussed in a later chapter. At this point, it is only meant to give
 557you a idea of what a device-tree looks like. I have purposefully kept
 558the "name" and "linux,phandle" properties which aren't necessary in
 559order to give you a better idea of what the tree looks like in
 560practice.
 561
 562  / o device-tree
 563      |- name = "device-tree"
 564      |- model = "MyBoardName"
 565      |- compatible = "MyBoardFamilyName"
 566      |- #address-cells = <2>
 567      |- #size-cells = <2>
 568      |- linux,phandle = <0>
 569      |
 570      o cpus
 571      | | - name = "cpus"
 572      | | - linux,phandle = <1>
 573      | | - #address-cells = <1>
 574      | | - #size-cells = <0>
 575      | |
 576      | o PowerPC,970@0
 577      |   |- name = "PowerPC,970"
 578      |   |- device_type = "cpu"
 579      |   |- reg = <0>
 580      |   |- clock-frequency = <0x5f5e1000>
 581      |   |- 64-bit
 582      |   |- linux,phandle = <2>
 583      |
 584      o memory@0
 585      | |- name = "memory"
 586      | |- device_type = "memory"
 587      | |- reg = <0x00000000 0x00000000 0x00000000 0x20000000>
 588      | |- linux,phandle = <3>
 589      |
 590      o chosen
 591        |- name = "chosen"
 592        |- bootargs = "root=/dev/sda2"
 593        |- linux,phandle = <4>
 594
 595This tree is almost a minimal tree. It pretty much contains the
 596minimal set of required nodes and properties to boot a linux kernel;
 597that is, some basic model information at the root, the CPUs, and the
 598physical memory layout.  It also includes misc information passed
 599through /chosen, like in this example, the platform type (mandatory)
 600and the kernel command line arguments (optional).
 601
 602The /cpus/PowerPC,970@0/64-bit property is an example of a
 603property without a value. All other properties have a value. The
 604significance of the #address-cells and #size-cells properties will be
 605explained in chapter IV which defines precisely the required nodes and
 606properties and their content.
 607
 608
 6093) Device tree "structure" block
 610
 611The structure of the device tree is a linearized tree structure. The
 612"OF_DT_BEGIN_NODE" token starts a new node, and the "OF_DT_END_NODE"
 613ends that node definition. Child nodes are simply defined before
 614"OF_DT_END_NODE" (that is nodes within the node). A 'token' is a 32
 615bit value. The tree has to be "finished" with a OF_DT_END token
 616
 617Here's the basic structure of a single node:
 618
 619     * token OF_DT_BEGIN_NODE (that is 0x00000001)
 620     * for version 1 to 3, this is the node full path as a zero
 621       terminated string, starting with "/". For version 16 and later,
 622       this is the node unit name only (or an empty string for the
 623       root node)
 624     * [align gap to next 4 bytes boundary]
 625     * for each property:
 626        * token OF_DT_PROP (that is 0x00000003)
 627        * 32-bit value of property value size in bytes (or 0 if no
 628          value)
 629        * 32-bit value of offset in string block of property name
 630        * property value data if any
 631        * [align gap to next 4 bytes boundary]
 632     * [child nodes if any]
 633     * token OF_DT_END_NODE (that is 0x00000002)
 634
 635So the node content can be summarized as a start token, a full path,
 636a list of properties, a list of child nodes, and an end token. Every
 637child node is a full node structure itself as defined above.
 638
 639NOTE: The above definition requires that all property definitions for
 640a particular node MUST precede any subnode definitions for that node.
 641Although the structure would not be ambiguous if properties and
 642subnodes were intermingled, the kernel parser requires that the
 643properties come first (up until at least 2.6.22).  Any tools
 644manipulating a flattened tree must take care to preserve this
 645constraint.
 646
 6474) Device tree "strings" block
 648
 649In order to save space, property names, which are generally redundant,
 650are stored separately in the "strings" block. This block is simply the
 651whole bunch of zero terminated strings for all property names
 652concatenated together. The device-tree property definitions in the
 653structure block will contain offset values from the beginning of the
 654strings block.
 655
 656
 657III - Required content of the device tree
 658=========================================
 659
 660WARNING: All "linux,*" properties defined in this document apply only
 661to a flattened device-tree. If your platform uses a real
 662implementation of Open Firmware or an implementation compatible with
 663the Open Firmware client interface, those properties will be created
 664by the trampoline code in the kernel's prom_init() file. For example,
 665that's where you'll have to add code to detect your board model and
 666set the platform number. However, when using the flattened device-tree
 667entry point, there is no prom_init() pass, and thus you have to
 668provide those properties yourself.
 669
 670
 6711) Note about cells and address representation
 672----------------------------------------------
 673
 674The general rule is documented in the various Open Firmware
 675documentations. If you choose to describe a bus with the device-tree
 676and there exist an OF bus binding, then you should follow the
 677specification. However, the kernel does not require every single
 678device or bus to be described by the device tree.
 679
 680In general, the format of an address for a device is defined by the
 681parent bus type, based on the #address-cells and #size-cells
 682properties.  Note that the parent's parent definitions of #address-cells
 683and #size-cells are not inherited so every node with children must specify
 684them.  The kernel requires the root node to have those properties defining
 685addresses format for devices directly mapped on the processor bus.
 686
 687Those 2 properties define 'cells' for representing an address and a
 688size. A "cell" is a 32-bit number. For example, if both contain 2
 689like the example tree given above, then an address and a size are both
 690composed of 2 cells, and each is a 64-bit number (cells are
 691concatenated and expected to be in big endian format). Another example
 692is the way Apple firmware defines them, with 2 cells for an address
 693and one cell for a size.  Most 32-bit implementations should define
 694#address-cells and #size-cells to 1, which represents a 32-bit value.
 695Some 32-bit processors allow for physical addresses greater than 32
 696bits; these processors should define #address-cells as 2.
 697
 698"reg" properties are always a tuple of the type "address size" where
 699the number of cells of address and size is specified by the bus
 700#address-cells and #size-cells. When a bus supports various address
 701spaces and other flags relative to a given address allocation (like
 702prefetchable, etc...) those flags are usually added to the top level
 703bits of the physical address. For example, a PCI physical address is
 704made of 3 cells, the bottom two containing the actual address itself
 705while the top cell contains address space indication, flags, and pci
 706bus & device numbers.
 707
 708For buses that support dynamic allocation, it's the accepted practice
 709to then not provide the address in "reg" (keep it 0) though while
 710providing a flag indicating the address is dynamically allocated, and
 711then, to provide a separate "assigned-addresses" property that
 712contains the fully allocated addresses. See the PCI OF bindings for
 713details.
 714
 715In general, a simple bus with no address space bits and no dynamic
 716allocation is preferred if it reflects your hardware, as the existing
 717kernel address parsing functions will work out of the box. If you
 718define a bus type with a more complex address format, including things
 719like address space bits, you'll have to add a bus translator to the
 720prom_parse.c file of the recent kernels for your bus type.
 721
 722The "reg" property only defines addresses and sizes (if #size-cells is
 723non-0) within a given bus. In order to translate addresses upward
 724(that is into parent bus addresses, and possibly into CPU physical
 725addresses), all buses must contain a "ranges" property. If the
 726"ranges" property is missing at a given level, it's assumed that
 727translation isn't possible, i.e., the registers are not visible on the
 728parent bus.  The format of the "ranges" property for a bus is a list
 729of:
 730
 731        bus address, parent bus address, size
 732
 733"bus address" is in the format of the bus this bus node is defining,
 734that is, for a PCI bridge, it would be a PCI address. Thus, (bus
 735address, size) defines a range of addresses for child devices. "parent
 736bus address" is in the format of the parent bus of this bus. For
 737example, for a PCI host controller, that would be a CPU address. For a
 738PCI<->ISA bridge, that would be a PCI address. It defines the base
 739address in the parent bus where the beginning of that range is mapped.
 740
 741For new 64-bit board support, I recommend either the 2/2 format or
 742Apple's 2/1 format which is slightly more compact since sizes usually
 743fit in a single 32-bit word.   New 32-bit board support should use a
 7441/1 format, unless the processor supports physical addresses greater
 745than 32-bits, in which case a 2/1 format is recommended.
 746
 747Alternatively, the "ranges" property may be empty, indicating that the
 748registers are visible on the parent bus using an identity mapping
 749translation.  In other words, the parent bus address space is the same
 750as the child bus address space.
 751
 7522) Note about "compatible" properties
 753-------------------------------------
 754
 755These properties are optional, but recommended in devices and the root
 756node. The format of a "compatible" property is a list of concatenated
 757zero terminated strings. They allow a device to express its
 758compatibility with a family of similar devices, in some cases,
 759allowing a single driver to match against several devices regardless
 760of their actual names.
 761
 7623) Note about "name" properties
 763-------------------------------
 764
 765While earlier users of Open Firmware like OldWorld macintoshes tended
 766to use the actual device name for the "name" property, it's nowadays
 767considered a good practice to use a name that is closer to the device
 768class (often equal to device_type). For example, nowadays, Ethernet
 769controllers are named "ethernet", an additional "model" property
 770defining precisely the chip type/model, and "compatible" property
 771defining the family in case a single driver can driver more than one
 772of these chips. However, the kernel doesn't generally put any
 773restriction on the "name" property; it is simply considered good
 774practice to follow the standard and its evolutions as closely as
 775possible.
 776
 777Note also that the new format version 16 makes the "name" property
 778optional. If it's absent for a node, then the node's unit name is then
 779used to reconstruct the name. That is, the part of the unit name
 780before the "@" sign is used (or the entire unit name if no "@" sign
 781is present).
 782
 7834) Note about node and property names and character set
 784-------------------------------------------------------
 785
 786While Open Firmware provides more flexible usage of 8859-1, this
 787specification enforces more strict rules. Nodes and properties should
 788be comprised only of ASCII characters 'a' to 'z', '0' to
 789'9', ',', '.', '_', '+', '#', '?', and '-'. Node names additionally
 790allow uppercase characters 'A' to 'Z' (property names should be
 791lowercase. The fact that vendors like Apple don't respect this rule is
 792irrelevant here). Additionally, node and property names should always
 793begin with a character in the range 'a' to 'z' (or 'A' to 'Z' for node
 794names).
 795
 796The maximum number of characters for both nodes and property names
 797is 31. In the case of node names, this is only the leftmost part of
 798a unit name (the pure "name" property), it doesn't include the unit
 799address which can extend beyond that limit.
 800
 801
 8025) Required nodes and properties
 803--------------------------------
 804  These are all that are currently required. However, it is strongly
 805  recommended that you expose PCI host bridges as documented in the
 806  PCI binding to Open Firmware, and your interrupt tree as documented
 807  in OF interrupt tree specification.
 808
 809  a) The root node
 810
 811  The root node requires some properties to be present:
 812
 813    - model : this is your board name/model
 814    - #address-cells : address representation for "root" devices
 815    - #size-cells: the size representation for "root" devices
 816    - compatible : the board "family" generally finds its way here,
 817      for example, if you have 2 board models with a similar layout,
 818      that typically get driven by the same platform code in the
 819      kernel, you would specify the exact board model in the
 820      compatible property followed by an entry that represents the SoC
 821      model.
 822
 823  The root node is also generally where you add additional properties
 824  specific to your board like the serial number if any, that sort of
 825  thing. It is recommended that if you add any "custom" property whose
 826  name may clash with standard defined ones, you prefix them with your
 827  vendor name and a comma.
 828
 829  b) The /cpus node
 830
 831  This node is the parent of all individual CPU nodes. It doesn't
 832  have any specific requirements, though it's generally good practice
 833  to have at least:
 834
 835               #address-cells = <00000001>
 836               #size-cells    = <00000000>
 837
 838  This defines that the "address" for a CPU is a single cell, and has
 839  no meaningful size. This is not necessary but the kernel will assume
 840  that format when reading the "reg" properties of a CPU node, see
 841  below
 842
 843  c) The /cpus/* nodes
 844
 845  So under /cpus, you are supposed to create a node for every CPU on
 846  the machine. There is no specific restriction on the name of the
 847  CPU, though it's common to call it <architecture>,<core>. For
 848  example, Apple uses PowerPC,G5 while IBM uses PowerPC,970FX.
 849  However, the Generic Names convention suggests that it would be
 850  better to simply use 'cpu' for each cpu node and use the compatible
 851  property to identify the specific cpu core.
 852
 853  Required properties:
 854
 855    - device_type : has to be "cpu"
 856    - reg : This is the physical CPU number, it's a single 32-bit cell
 857      and is also used as-is as the unit number for constructing the
 858      unit name in the full path. For example, with 2 CPUs, you would
 859      have the full path:
 860        /cpus/PowerPC,970FX@0
 861        /cpus/PowerPC,970FX@1
 862      (unit addresses do not require leading zeroes)
 863    - d-cache-block-size : one cell, L1 data cache block size in bytes (*)
 864    - i-cache-block-size : one cell, L1 instruction cache block size in
 865      bytes
 866    - d-cache-size : one cell, size of L1 data cache in bytes
 867    - i-cache-size : one cell, size of L1 instruction cache in bytes
 868
 869(*) The cache "block" size is the size on which the cache management
 870instructions operate. Historically, this document used the cache
 871"line" size here which is incorrect. The kernel will prefer the cache
 872block size and will fallback to cache line size for backward
 873compatibility.
 874
 875  Recommended properties:
 876
 877    - timebase-frequency : a cell indicating the frequency of the
 878      timebase in Hz. This is not directly used by the generic code,
 879      but you are welcome to copy/paste the pSeries code for setting
 880      the kernel timebase/decrementer calibration based on this
 881      value.
 882    - clock-frequency : a cell indicating the CPU core clock frequency
 883      in Hz. A new property will be defined for 64-bit values, but if
 884      your frequency is < 4Ghz, one cell is enough. Here as well as
 885      for the above, the common code doesn't use that property, but
 886      you are welcome to re-use the pSeries or Maple one. A future
 887      kernel version might provide a common function for this.
 888    - d-cache-line-size : one cell, L1 data cache line size in bytes
 889      if different from the block size
 890    - i-cache-line-size : one cell, L1 instruction cache line size in
 891      bytes if different from the block size
 892
 893  You are welcome to add any property you find relevant to your board,
 894  like some information about the mechanism used to soft-reset the
 895  CPUs. For example, Apple puts the GPIO number for CPU soft reset
 896  lines in there as a "soft-reset" property since they start secondary
 897  CPUs by soft-resetting them.
 898
 899
 900  d) the /memory node(s)
 901
 902  To define the physical memory layout of your board, you should
 903  create one or more memory node(s). You can either create a single
 904  node with all memory ranges in its reg property, or you can create
 905  several nodes, as you wish. The unit address (@ part) used for the
 906  full path is the address of the first range of memory defined by a
 907  given node. If you use a single memory node, this will typically be
 908  @0.
 909
 910  Required properties:
 911
 912    - device_type : has to be "memory"
 913    - reg : This property contains all the physical memory ranges of
 914      your board. It's a list of addresses/sizes concatenated
 915      together, with the number of cells of each defined by the
 916      #address-cells and #size-cells of the root node. For example,
 917      with both of these properties being 2 like in the example given
 918      earlier, a 970 based machine with 6Gb of RAM could typically
 919      have a "reg" property here that looks like:
 920
 921      00000000 00000000 00000000 80000000
 922      00000001 00000000 00000001 00000000
 923
 924      That is a range starting at 0 of 0x80000000 bytes and a range
 925      starting at 0x100000000 and of 0x100000000 bytes. You can see
 926      that there is no memory covering the IO hole between 2Gb and
 927      4Gb. Some vendors prefer splitting those ranges into smaller
 928      segments, but the kernel doesn't care.
 929
 930  e) The /chosen node
 931
 932  This node is a bit "special". Normally, that's where Open Firmware
 933  puts some variable environment information, like the arguments, or
 934  the default input/output devices.
 935
 936  This specification makes a few of these mandatory, but also defines
 937  some linux-specific properties that would be normally constructed by
 938  the prom_init() trampoline when booting with an OF client interface,
 939  but that you have to provide yourself when using the flattened format.
 940
 941  Recommended properties:
 942
 943    - bootargs : This zero-terminated string is passed as the kernel
 944      command line
 945    - linux,stdout-path : This is the full path to your standard
 946      console device if any. Typically, if you have serial devices on
 947      your board, you may want to put the full path to the one set as
 948      the default console in the firmware here, for the kernel to pick
 949      it up as its own default console.
 950
 951  Note that u-boot creates and fills in the chosen node for platforms
 952  that use it.
 953
 954  (Note: a practice that is now obsolete was to include a property
 955  under /chosen called interrupt-controller which had a phandle value
 956  that pointed to the main interrupt controller)
 957
 958  f) the /soc<SOCname> node
 959
 960  This node is used to represent a system-on-a-chip (SoC) and must be
 961  present if the processor is a SoC. The top-level soc node contains
 962  information that is global to all devices on the SoC. The node name
 963  should contain a unit address for the SoC, which is the base address
 964  of the memory-mapped register set for the SoC. The name of an SoC
 965  node should start with "soc", and the remainder of the name should
 966  represent the part number for the soc.  For example, the MPC8540's
 967  soc node would be called "soc8540".
 968
 969  Required properties:
 970
 971    - ranges : Should be defined as specified in 1) to describe the
 972      translation of SoC addresses for memory mapped SoC registers.
 973    - bus-frequency: Contains the bus frequency for the SoC node.
 974      Typically, the value of this field is filled in by the boot
 975      loader.
 976    - compatible : Exact model of the SoC
 977
 978
 979  Recommended properties:
 980
 981    - reg : This property defines the address and size of the
 982      memory-mapped registers that are used for the SOC node itself.
 983      It does not include the child device registers - these will be
 984      defined inside each child node.  The address specified in the
 985      "reg" property should match the unit address of the SOC node.
 986    - #address-cells : Address representation for "soc" devices.  The
 987      format of this field may vary depending on whether or not the
 988      device registers are memory mapped.  For memory mapped
 989      registers, this field represents the number of cells needed to
 990      represent the address of the registers.  For SOCs that do not
 991      use MMIO, a special address format should be defined that
 992      contains enough cells to represent the required information.
 993      See 1) above for more details on defining #address-cells.
 994    - #size-cells : Size representation for "soc" devices
 995    - #interrupt-cells : Defines the width of cells used to represent
 996       interrupts.  Typically this value is <2>, which includes a
 997       32-bit number that represents the interrupt number, and a
 998       32-bit number that represents the interrupt sense and level.
 999       This field is only needed if the SOC contains an interrupt
1000       controller.
1001
1002  The SOC node may contain child nodes for each SOC device that the
1003  platform uses.  Nodes should not be created for devices which exist
1004  on the SOC but are not used by a particular platform. See chapter VI
1005  for more information on how to specify devices that are part of a SOC.
1006
1007  Example SOC node for the MPC8540:
1008
1009        soc8540@e0000000 {
1010                #address-cells = <1>;
1011                #size-cells = <1>;
1012                #interrupt-cells = <2>;
1013                device_type = "soc";
1014                ranges = <0x00000000 0xe0000000 0x00100000>
1015                reg = <0xe0000000 0x00003000>;
1016                bus-frequency = <0>;
1017        }
1018
1019
1020
1021IV - "dtc", the device tree compiler
1022====================================
1023
1024
1025dtc source code can be found at
1026<http://git.jdl.com/gitweb/?p=dtc.git>
1027
1028WARNING: This version is still in early development stage; the
1029resulting device-tree "blobs" have not yet been validated with the
1030kernel. The current generated block lacks a useful reserve map (it will
1031be fixed to generate an empty one, it's up to the bootloader to fill
1032it up) among others. The error handling needs work, bugs are lurking,
1033etc...
1034
1035dtc basically takes a device-tree in a given format and outputs a
1036device-tree in another format. The currently supported formats are:
1037
1038  Input formats:
1039  -------------
1040
1041     - "dtb": "blob" format, that is a flattened device-tree block
1042       with
1043        header all in a binary blob.
1044     - "dts": "source" format. This is a text file containing a
1045       "source" for a device-tree. The format is defined later in this
1046        chapter.
1047     - "fs" format. This is a representation equivalent to the
1048        output of /proc/device-tree, that is nodes are directories and
1049        properties are files
1050
1051 Output formats:
1052 ---------------
1053
1054     - "dtb": "blob" format
1055     - "dts": "source" format
1056     - "asm": assembly language file. This is a file that can be
1057       sourced by gas to generate a device-tree "blob". That file can
1058       then simply be added to your Makefile. Additionally, the
1059       assembly file exports some symbols that can be used.
1060
1061
1062The syntax of the dtc tool is
1063
1064    dtc [-I <input-format>] [-O <output-format>]
1065        [-o output-filename] [-V output_version] input_filename
1066
1067
1068The "output_version" defines what version of the "blob" format will be
1069generated. Supported versions are 1,2,3 and 16. The default is
1070currently version 3 but that may change in the future to version 16.
1071
1072Additionally, dtc performs various sanity checks on the tree, like the
1073uniqueness of linux, phandle properties, validity of strings, etc...
1074
1075The format of the .dts "source" file is "C" like, supports C and C++
1076style comments.
1077
1078/ {
1079}
1080
1081The above is the "device-tree" definition. It's the only statement
1082supported currently at the toplevel.
1083
1084/ {
1085  property1 = "string_value";   /* define a property containing a 0
1086                                 * terminated string
1087                                 */
1088
1089  property2 = <0x1234abcd>;     /* define a property containing a
1090                                 * numerical 32-bit value (hexadecimal)
1091                                 */
1092
1093  property3 = <0x12345678 0x12345678 0xdeadbeef>;
1094                                /* define a property containing 3
1095                                 * numerical 32-bit values (cells) in
1096                                 * hexadecimal
1097                                 */
1098  property4 = [0x0a 0x0b 0x0c 0x0d 0xde 0xea 0xad 0xbe 0xef];
1099                                /* define a property whose content is
1100                                 * an arbitrary array of bytes
1101                                 */
1102
1103  childnode@address {   /* define a child node named "childnode"
1104                                 * whose unit name is "childnode at
1105                                 * address"
1106                                 */
1107
1108    childprop = "hello\n";      /* define a property "childprop" of
1109                                 * childnode (in this case, a string)
1110                                 */
1111  };
1112};
1113
1114Nodes can contain other nodes etc... thus defining the hierarchical
1115structure of the tree.
1116
1117Strings support common escape sequences from C: "\n", "\t", "\r",
1118"\(octal value)", "\x(hex value)".
1119
1120It is also suggested that you pipe your source file through cpp (gcc
1121preprocessor) so you can use #include's, #define for constants, etc...
1122
1123Finally, various options are planned but not yet implemented, like
1124automatic generation of phandles, labels (exported to the asm file so
1125you can point to a property content and change it easily from whatever
1126you link the device-tree with), label or path instead of numeric value
1127in some cells to "point" to a node (replaced by a phandle at compile
1128time), export of reserve map address to the asm file, ability to
1129specify reserve map content at compile time, etc...
1130
1131We may provide a .h include file with common definitions of that
1132proves useful for some properties (like building PCI properties or
1133interrupt maps) though it may be better to add a notion of struct
1134definitions to the compiler...
1135
1136
1137V - Recommendations for a bootloader
1138====================================
1139
1140
1141Here are some various ideas/recommendations that have been proposed
1142while all this has been defined and implemented.
1143
1144  - The bootloader may want to be able to use the device-tree itself
1145    and may want to manipulate it (to add/edit some properties,
1146    like physical memory size or kernel arguments). At this point, 2
1147    choices can be made. Either the bootloader works directly on the
1148    flattened format, or the bootloader has its own internal tree
1149    representation with pointers (similar to the kernel one) and
1150    re-flattens the tree when booting the kernel. The former is a bit
1151    more difficult to edit/modify, the later requires probably a bit
1152    more code to handle the tree structure. Note that the structure
1153    format has been designed so it's relatively easy to "insert"
1154    properties or nodes or delete them by just memmoving things
1155    around. It contains no internal offsets or pointers for this
1156    purpose.
1157
1158  - An example of code for iterating nodes & retrieving properties
1159    directly from the flattened tree format can be found in the kernel
1160    file drivers/of/fdt.c.  Look at the of_scan_flat_dt() function,
1161    its usage in early_init_devtree(), and the corresponding various
1162    early_init_dt_scan_*() callbacks. That code can be re-used in a
1163    GPL bootloader, and as the author of that code, I would be happy
1164    to discuss possible free licensing to any vendor who wishes to
1165    integrate all or part of this code into a non-GPL bootloader.
1166    (reference needed; who is 'I' here? ---gcl Jan 31, 2011)
1167
1168
1169
1170VI - System-on-a-chip devices and nodes
1171=======================================
1172
1173Many companies are now starting to develop system-on-a-chip
1174processors, where the processor core (CPU) and many peripheral devices
1175exist on a single piece of silicon.  For these SOCs, an SOC node
1176should be used that defines child nodes for the devices that make
1177up the SOC. While platforms are not required to use this model in
1178order to boot the kernel, it is highly encouraged that all SOC
1179implementations define as complete a flat-device-tree as possible to
1180describe the devices on the SOC.  This will allow for the
1181genericization of much of the kernel code.
1182
1183
11841) Defining child nodes of an SOC
1185---------------------------------
1186
1187Each device that is part of an SOC may have its own node entry inside
1188the SOC node.  For each device that is included in the SOC, the unit
1189address property represents the address offset for this device's
1190memory-mapped registers in the parent's address space.  The parent's
1191address space is defined by the "ranges" property in the top-level soc
1192node. The "reg" property for each node that exists directly under the
1193SOC node should contain the address mapping from the child address space
1194to the parent SOC address space and the size of the device's
1195memory-mapped register file.
1196
1197For many devices that may exist inside an SOC, there are predefined
1198specifications for the format of the device tree node.  All SOC child
1199nodes should follow these specifications, except where noted in this
1200document.
1201
1202See appendix A for an example partial SOC node definition for the
1203MPC8540.
1204
1205
12062) Representing devices without a current OF specification
1207----------------------------------------------------------
1208
1209Currently, there are many devices on SoCs that do not have a standard
1210representation defined as part of the Open Firmware specifications,
1211mainly because the boards that contain these SoCs are not currently
1212booted using Open Firmware.  Binding documentation for new devices
1213should be added to the Documentation/devicetree/bindings directory.
1214That directory will expand as device tree support is added to more and
1215more SoCs.
1216
1217
1218VII - Specifying interrupt information for devices
1219===================================================
1220
1221The device tree represents the buses and devices of a hardware
1222system in a form similar to the physical bus topology of the
1223hardware.
1224
1225In addition, a logical 'interrupt tree' exists which represents the
1226hierarchy and routing of interrupts in the hardware.
1227
1228The interrupt tree model is fully described in the
1229document "Open Firmware Recommended Practice: Interrupt
1230Mapping Version 0.9".  The document is available at:
1231<http://playground.sun.com/1275/practice>.
1232
12331) interrupts property
1234----------------------
1235
1236Devices that generate interrupts to a single interrupt controller
1237should use the conventional OF representation described in the
1238OF interrupt mapping documentation.
1239
1240Each device which generates interrupts must have an 'interrupt'
1241property.  The interrupt property value is an arbitrary number of
1242of 'interrupt specifier' values which describe the interrupt or
1243interrupts for the device.
1244
1245The encoding of an interrupt specifier is determined by the
1246interrupt domain in which the device is located in the
1247interrupt tree.  The root of an interrupt domain specifies in
1248its #interrupt-cells property the number of 32-bit cells
1249required to encode an interrupt specifier.  See the OF interrupt
1250mapping documentation for a detailed description of domains.
1251
1252For example, the binding for the OpenPIC interrupt controller
1253specifies  an #interrupt-cells value of 2 to encode the interrupt
1254number and level/sense information. All interrupt children in an
1255OpenPIC interrupt domain use 2 cells per interrupt in their interrupts
1256property.
1257
1258The PCI bus binding specifies a #interrupt-cell value of 1 to encode
1259which interrupt pin (INTA,INTB,INTC,INTD) is used.
1260
12612) interrupt-parent property
1262----------------------------
1263
1264The interrupt-parent property is specified to define an explicit
1265link between a device node and its interrupt parent in
1266the interrupt tree.  The value of interrupt-parent is the
1267phandle of the parent node.
1268
1269If the interrupt-parent property is not defined for a node, its
1270interrupt parent is assumed to be an ancestor in the node's
1271_device tree_ hierarchy.
1272
12733) OpenPIC Interrupt Controllers
1274--------------------------------
1275
1276OpenPIC interrupt controllers require 2 cells to encode
1277interrupt information.  The first cell defines the interrupt
1278number.  The second cell defines the sense and level
1279information.
1280
1281Sense and level information should be encoded as follows:
1282
1283        0 = low to high edge sensitive type enabled
1284        1 = active low level sensitive type enabled
1285        2 = active high level sensitive type enabled
1286        3 = high to low edge sensitive type enabled
1287
12884) ISA Interrupt Controllers
1289----------------------------
1290
1291ISA PIC interrupt controllers require 2 cells to encode
1292interrupt information.  The first cell defines the interrupt
1293number.  The second cell defines the sense and level
1294information.
1295
1296ISA PIC interrupt controllers should adhere to the ISA PIC
1297encodings listed below:
1298
1299        0 =  active low level sensitive type enabled
1300        1 =  active high level sensitive type enabled
1301        2 =  high to low edge sensitive type enabled
1302        3 =  low to high edge sensitive type enabled
1303
1304VIII - Specifying Device Power Management Information (sleep property)
1305===================================================================
1306
1307Devices on SOCs often have mechanisms for placing devices into low-power
1308states that are decoupled from the devices' own register blocks.  Sometimes,
1309this information is more complicated than a cell-index property can
1310reasonably describe.  Thus, each device controlled in such a manner
1311may contain a "sleep" property which describes these connections.
1312
1313The sleep property consists of one or more sleep resources, each of
1314which consists of a phandle to a sleep controller, followed by a
1315controller-specific sleep specifier of zero or more cells.
1316
1317The semantics of what type of low power modes are possible are defined
1318by the sleep controller.  Some examples of the types of low power modes
1319that may be supported are:
1320
1321 - Dynamic: The device may be disabled or enabled at any time.
1322 - System Suspend: The device may request to be disabled or remain
1323   awake during system suspend, but will not be disabled until then.
1324 - Permanent: The device is disabled permanently (until the next hard
1325   reset).
1326
1327Some devices may share a clock domain with each other, such that they should
1328only be suspended when none of the devices are in use.  Where reasonable,
1329such nodes should be placed on a virtual bus, where the bus has the sleep
1330property.  If the clock domain is shared among devices that cannot be
1331reasonably grouped in this manner, then create a virtual sleep controller
1332(similar to an interrupt nexus, except that defining a standardized
1333sleep-map should wait until its necessity is demonstrated).
1334
1335Appendix A - Sample SOC node for MPC8540
1336========================================
1337
1338        soc@e0000000 {
1339                #address-cells = <1>;
1340                #size-cells = <1>;
1341                compatible = "fsl,mpc8540-ccsr", "simple-bus";
1342                device_type = "soc";
1343                ranges = <0x00000000 0xe0000000 0x00100000>
1344                bus-frequency = <0>;
1345                interrupt-parent = <&pic>;
1346
1347                ethernet@24000 {
1348                        #address-cells = <1>;
1349                        #size-cells = <1>;
1350                        device_type = "network";
1351                        model = "TSEC";
1352                        compatible = "gianfar", "simple-bus";
1353                        reg = <0x24000 0x1000>;
1354                        local-mac-address = [ 0x00 0xE0 0x0C 0x00 0x73 0x00 ];
1355                        interrupts = <0x29 2 0x30 2 0x34 2>;
1356                        phy-handle = <&phy0>;
1357                        sleep = <&pmc 0x00000080>;
1358                        ranges;
1359
1360                        mdio@24520 {
1361                                reg = <0x24520 0x20>;
1362                                compatible = "fsl,gianfar-mdio";
1363
1364                                phy0: ethernet-phy@0 {
1365                                        interrupts = <5 1>;
1366                                        reg = <0>;
1367                                        device_type = "ethernet-phy";
1368                                };
1369
1370                                phy1: ethernet-phy@1 {
1371                                        interrupts = <5 1>;
1372                                        reg = <1>;
1373                                        device_type = "ethernet-phy";
1374                                };
1375
1376                                phy3: ethernet-phy@3 {
1377                                        interrupts = <7 1>;
1378                                        reg = <3>;
1379                                        device_type = "ethernet-phy";
1380                                };
1381                        };
1382                };
1383
1384                ethernet@25000 {
1385                        device_type = "network";
1386                        model = "TSEC";
1387                        compatible = "gianfar";
1388                        reg = <0x25000 0x1000>;
1389                        local-mac-address = [ 0x00 0xE0 0x0C 0x00 0x73 0x01 ];
1390                        interrupts = <0x13 2 0x14 2 0x18 2>;
1391                        phy-handle = <&phy1>;
1392                        sleep = <&pmc 0x00000040>;
1393                };
1394
1395                ethernet@26000 {
1396                        device_type = "network";
1397                        model = "FEC";
1398                        compatible = "gianfar";
1399                        reg = <0x26000 0x1000>;
1400                        local-mac-address = [ 0x00 0xE0 0x0C 0x00 0x73 0x02 ];
1401                        interrupts = <0x41 2>;
1402                        phy-handle = <&phy3>;
1403                        sleep = <&pmc 0x00000020>;
1404                };
1405
1406                serial@4500 {
1407                        #address-cells = <1>;
1408                        #size-cells = <1>;
1409                        compatible = "fsl,mpc8540-duart", "simple-bus";
1410                        sleep = <&pmc 0x00000002>;
1411                        ranges;
1412
1413                        serial@4500 {
1414                                device_type = "serial";
1415                                compatible = "ns16550";
1416                                reg = <0x4500 0x100>;
1417                                clock-frequency = <0>;
1418                                interrupts = <0x42 2>;
1419                        };
1420
1421                        serial@4600 {
1422                                device_type = "serial";
1423                                compatible = "ns16550";
1424                                reg = <0x4600 0x100>;
1425                                clock-frequency = <0>;
1426                                interrupts = <0x42 2>;
1427                        };
1428                };
1429
1430                pic: pic@40000 {
1431                        interrupt-controller;
1432                        #address-cells = <0>;
1433                        #interrupt-cells = <2>;
1434                        reg = <0x40000 0x40000>;
1435                        compatible = "chrp,open-pic";
1436                        device_type = "open-pic";
1437                };
1438
1439                i2c@3000 {
1440                        interrupts = <0x43 2>;
1441                        reg = <0x3000 0x100>;
1442                        compatible  = "fsl-i2c";
1443                        dfsrr;
1444                        sleep = <&pmc 0x00000004>;
1445                };
1446
1447                pmc: power@e0070 {
1448                        compatible = "fsl,mpc8540-pmc", "fsl,mpc8548-pmc";
1449                        reg = <0xe0070 0x20>;
1450                };
1451        };
1452
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.