manual.txt revision 204431
1Device Tree Compiler Manual 2=========================== 3 4I - "dtc", the device tree compiler 5 1) Obtaining Sources 6 2) Description 7 3) Command Line 8 4) Source File 9 4.1) Overview 10 4.2) Properties 11 4.3) Labels and References 12 13II - The DT block format 14 1) Header 15 2) Device tree generalities 16 3) Device tree "structure" block 17 4) Device tree "strings" block 18 19 20III - libfdt 21 22 23I - "dtc", the device tree compiler 24=================================== 25 261) Sources 27 28Source code for the Device Tree Compiler can be found at jdl.com. 29The gitweb interface is: 30 31 http://www.jdl.com/git_repos/ 32 33The repository is here: 34 35 git://www.jdl.com/software/dtc.git 36 http://www.jdl.com/software/dtc.git 37 38Tarballs of the 1.0.0 and latest releases are here: 39 40 http://www.jdl.com/software/dtc-1.0.0.tgz 41 http://www.jdl.com/software/dtc-latest.tgz 42 43 442) Description 45 46The Device Tree Compiler, dtc, takes as input a device-tree in 47a given format and outputs a device-tree in another format. 48Typically, the input format is "dts", a human readable source 49format, and creates a "dtb", or binary format as output. 50 51The currently supported Input Formats are: 52 53 - "dtb": "blob" format. A flattened device-tree block with 54 header in one binary blob. 55 56 - "dts": "source" format. A text file containing a "source" 57 for a device-tree. 58 59 - "fs" format. A representation equivalent to the output of 60 /proc/device-tree where nodes are directories and 61 properties are files. 62 63The currently supported Output Formats are: 64 65 - "dtb": "blob" format 66 67 - "dts": "source" format 68 69 - "asm": assembly language file. A file that can be sourced 70 by gas to generate a device-tree "blob". That file can 71 then simply be added to your Makefile. Additionally, the 72 assembly file exports some symbols that can be used. 73 74 753) Command Line 76 77The syntax of the dtc command line is: 78 79 dtc [options] [<input_filename>] 80 81Options: 82 83 <input_filename> 84 The name of the input source file. If no <input_filename> 85 or "-" is given, stdin is used. 86 87 -b <number> 88 Set the physical boot cpu. 89 90 -f 91 Force. Try to produce output even if the input tree has errors. 92 93 -h 94 Emit a brief usage and help message. 95 96 -I <input_format> 97 The source input format, as listed above. 98 99 -o <output_filename> 100 The name of the generated output file. Use "-" for stdout. 101 102 -O <output_format> 103 The generated output format, as listed above. 104 105 -q 106 Quiet: -q suppress warnings, -qq errors, -qqq all 107 108 -R <number> 109 Make space for <number> reserve map entries 110 Relevant for dtb and asm output only. 111 112 -S <bytes> 113 Ensure the blob at least <bytes> long, adding additional 114 space if needed. 115 116 -v 117 Print DTC version and exit. 118 119 -V <output_version> 120 Generate output conforming to the given <output_version>. 121 By default the most recent version is generated. 122 Relevant for dtb and asm output only. 123 124 125The <output_version> defines what version of the "blob" format will be 126generated. Supported versions are 1, 2, 3, 16 and 17. The default is 127always the most recent version and is likely the highest number. 128 129Additionally, dtc performs various sanity checks on the tree. 130 131 1324) Device Tree Source file 133 1344.1) Overview 135 136Here is a very rough overview of the layout of a DTS source file: 137 138 139 sourcefile: list_of_memreserve devicetree 140 141 memreserve: label 'memreserve' ADDR ADDR ';' 142 | label 'memreserve' ADDR '-' ADDR ';' 143 144 devicetree: '/' nodedef 145 146 nodedef: '{' list_of_property list_of_subnode '}' ';' 147 148 property: label PROPNAME '=' propdata ';' 149 150 propdata: STRING 151 | '<' list_of_cells '>' 152 | '[' list_of_bytes ']' 153 154 subnode: label nodename nodedef 155 156That structure forms a hierarchical layout of nodes and properties 157rooted at an initial node as: 158 159 / { 160 } 161 162Both classic C style and C++ style comments are supported. 163 164Source files may be directly included using the syntax: 165 166 /include/ "filename" 167 168 1694.2) Properties 170 171Properties are named, possibly labeled, values. Each value 172is one of: 173 174 - A null-teminated C-like string, 175 - A numeric value fitting in 32 bits, 176 - A list of 32-bit values 177 - A byte sequence 178 179Here are some example property definitions: 180 181 - A property containing a 0 terminated string 182 183 property1 = "string_value"; 184 185 - A property containing a numerical 32-bit hexadecimal value 186 187 property2 = <1234abcd>; 188 189 - A property containing 3 numerical 32-bit hexadecimal values 190 191 property3 = <12345678 12345678 deadbeef>; 192 193 - A property whose content is an arbitrary array of bytes 194 195 property4 = [0a 0b 0c 0d de ea ad be ef]; 196 197 198Node may contain sub-nodes to obtain a hierarchical structure. 199For example: 200 201 - A child node named "childnode" whose unit name is 202 "childnode at address". It it turn has a string property 203 called "childprop". 204 205 childnode@addresss { 206 childprop = "hello\n"; 207 }; 208 209 210By default, all numeric values are hexadecimal. Alternate bases 211may be specified using a prefix "d#" for decimal, "b#" for binary, 212and "o#" for octal. 213 214Strings support common escape sequences from C: "\n", "\t", "\r", 215"\(octal value)", "\x(hex value)". 216 217 2184.3) Labels and References 219 220Labels may be applied to nodes or properties. Labels appear 221before a node name, and are referenced using an ampersand: &label. 222Absolute node path names are also allowed in node references. 223 224In this exmaple, a node is labled "mpic" and then referenced: 225 226 mpic: interrupt-controller@40000 { 227 ... 228 }; 229 230 ethernet-phy@3 { 231 interrupt-parent = <&mpic>; 232 ... 233 }; 234 235And used in properties, lables may appear before or after any value: 236 237 randomnode { 238 prop: string = data: "mystring\n" data_end: ; 239 ... 240 }; 241 242 243 244II - The DT block format 245======================== 246 247This chapter defines the format of the flattened device-tree 248passed to the kernel. The actual content of the device tree 249are described in the kernel documentation in the file 250 251 linux-2.6/Documentation/powerpc/booting-without-of.txt 252 253You can find example of code manipulating that format within 254the kernel. For example, the file: 255 256 including arch/powerpc/kernel/prom_init.c 257 258will generate a flattened device-tree from the Open Firmware 259representation. Other utilities such as fs2dt, which is part of 260the kexec tools, will generate one from a filesystem representation. 261Some bootloaders such as U-Boot provide a bit more support by 262using the libfdt code. 263 264For booting the kernel, the device tree block has to be in main memory. 265It has to be accessible in both real mode and virtual mode with no 266mapping other than main memory. If you are writing a simple flash 267bootloader, it should copy the block to RAM before passing it to 268the kernel. 269 270 2711) Header 272--------- 273 274The kernel is entered with r3 pointing to an area of memory that is 275roughly described in include/asm-powerpc/prom.h by the structure 276boot_param_header: 277 278 struct boot_param_header { 279 u32 magic; /* magic word OF_DT_HEADER */ 280 u32 totalsize; /* total size of DT block */ 281 u32 off_dt_struct; /* offset to structure */ 282 u32 off_dt_strings; /* offset to strings */ 283 u32 off_mem_rsvmap; /* offset to memory reserve map */ 284 u32 version; /* format version */ 285 u32 last_comp_version; /* last compatible version */ 286 287 /* version 2 fields below */ 288 u32 boot_cpuid_phys; /* Which physical CPU id we're 289 booting on */ 290 /* version 3 fields below */ 291 u32 size_dt_strings; /* size of the strings block */ 292 293 /* version 17 fields below */ 294 u32 size_dt_struct; /* size of the DT structure block */ 295 }; 296 297Along with the constants: 298 299 /* Definitions used by the flattened device tree */ 300 #define OF_DT_HEADER 0xd00dfeed /* 4: version, 301 4: total size */ 302 #define OF_DT_BEGIN_NODE 0x1 /* Start node: full name 303 */ 304 #define OF_DT_END_NODE 0x2 /* End node */ 305 #define OF_DT_PROP 0x3 /* Property: name off, 306 size, content */ 307 #define OF_DT_END 0x9 308 309All values in this header are in big endian format, the various 310fields in this header are defined more precisely below. All "offset" 311values are in bytes from the start of the header; that is from the 312value of r3. 313 314 - magic 315 316 This is a magic value that "marks" the beginning of the 317 device-tree block header. It contains the value 0xd00dfeed and is 318 defined by the constant OF_DT_HEADER 319 320 - totalsize 321 322 This is the total size of the DT block including the header. The 323 "DT" block should enclose all data structures defined in this 324 chapter (who are pointed to by offsets in this header). That is, 325 the device-tree structure, strings, and the memory reserve map. 326 327 - off_dt_struct 328 329 This is an offset from the beginning of the header to the start 330 of the "structure" part the device tree. (see 2) device tree) 331 332 - off_dt_strings 333 334 This is an offset from the beginning of the header to the start 335 of the "strings" part of the device-tree 336 337 - off_mem_rsvmap 338 339 This is an offset from the beginning of the header to the start 340 of the reserved memory map. This map is a list of pairs of 64- 341 bit integers. Each pair is a physical address and a size. The 342 list is terminated by an entry of size 0. This map provides the 343 kernel with a list of physical memory areas that are "reserved" 344 and thus not to be used for memory allocations, especially during 345 early initialization. The kernel needs to allocate memory during 346 boot for things like un-flattening the device-tree, allocating an 347 MMU hash table, etc... Those allocations must be done in such a 348 way to avoid overriding critical things like, on Open Firmware 349 capable machines, the RTAS instance, or on some pSeries, the TCE 350 tables used for the iommu. Typically, the reserve map should 351 contain _at least_ this DT block itself (header,total_size). If 352 you are passing an initrd to the kernel, you should reserve it as 353 well. You do not need to reserve the kernel image itself. The map 354 should be 64-bit aligned. 355 356 - version 357 358 This is the version of this structure. Version 1 stops 359 here. Version 2 adds an additional field boot_cpuid_phys. 360 Version 3 adds the size of the strings block, allowing the kernel 361 to reallocate it easily at boot and free up the unused flattened 362 structure after expansion. Version 16 introduces a new more 363 "compact" format for the tree itself that is however not backward 364 compatible. Version 17 adds an additional field, size_dt_struct, 365 allowing it to be reallocated or moved more easily (this is 366 particularly useful for bootloaders which need to make 367 adjustments to a device tree based on probed information). You 368 should always generate a structure of the highest version defined 369 at the time of your implementation. Currently that is version 17, 370 unless you explicitly aim at being backward compatible. 371 372 - last_comp_version 373 374 Last compatible version. This indicates down to what version of 375 the DT block you are backward compatible. For example, version 2 376 is backward compatible with version 1 (that is, a kernel build 377 for version 1 will be able to boot with a version 2 format). You 378 should put a 1 in this field if you generate a device tree of 379 version 1 to 3, or 16 if you generate a tree of version 16 or 17 380 using the new unit name format. 381 382 - boot_cpuid_phys 383 384 This field only exist on version 2 headers. It indicate which 385 physical CPU ID is calling the kernel entry point. This is used, 386 among others, by kexec. If you are on an SMP system, this value 387 should match the content of the "reg" property of the CPU node in 388 the device-tree corresponding to the CPU calling the kernel entry 389 point (see further chapters for more informations on the required 390 device-tree contents) 391 392 - size_dt_strings 393 394 This field only exists on version 3 and later headers. It 395 gives the size of the "strings" section of the device tree (which 396 starts at the offset given by off_dt_strings). 397 398 - size_dt_struct 399 400 This field only exists on version 17 and later headers. It gives 401 the size of the "structure" section of the device tree (which 402 starts at the offset given by off_dt_struct). 403 404So the typical layout of a DT block (though the various parts don't 405need to be in that order) looks like this (addresses go from top to 406bottom): 407 408 ------------------------------ 409 r3 -> | struct boot_param_header | 410 ------------------------------ 411 | (alignment gap) (*) | 412 ------------------------------ 413 | memory reserve map | 414 ------------------------------ 415 | (alignment gap) | 416 ------------------------------ 417 | | 418 | device-tree structure | 419 | | 420 ------------------------------ 421 | (alignment gap) | 422 ------------------------------ 423 | | 424 | device-tree strings | 425 | | 426 -----> ------------------------------ 427 | 428 | 429 --- (r3 + totalsize) 430 431 (*) The alignment gaps are not necessarily present; their presence 432 and size are dependent on the various alignment requirements of 433 the individual data blocks. 434 435 4362) Device tree generalities 437--------------------------- 438 439This device-tree itself is separated in two different blocks, a 440structure block and a strings block. Both need to be aligned to a 4 441byte boundary. 442 443First, let's quickly describe the device-tree concept before detailing 444the storage format. This chapter does _not_ describe the detail of the 445required types of nodes & properties for the kernel, this is done 446later in chapter III. 447 448The device-tree layout is strongly inherited from the definition of 449the Open Firmware IEEE 1275 device-tree. It's basically a tree of 450nodes, each node having two or more named properties. A property can 451have a value or not. 452 453It is a tree, so each node has one and only one parent except for the 454root node who has no parent. 455 456A node has 2 names. The actual node name is generally contained in a 457property of type "name" in the node property list whose value is a 458zero terminated string and is mandatory for version 1 to 3 of the 459format definition (as it is in Open Firmware). Version 16 makes it 460optional as it can generate it from the unit name defined below. 461 462There is also a "unit name" that is used to differentiate nodes with 463the same name at the same level, it is usually made of the node 464names, the "@" sign, and a "unit address", which definition is 465specific to the bus type the node sits on. 466 467The unit name doesn't exist as a property per-se but is included in 468the device-tree structure. It is typically used to represent "path" in 469the device-tree. More details about the actual format of these will be 470below. 471 472The kernel powerpc generic code does not make any formal use of the 473unit address (though some board support code may do) so the only real 474requirement here for the unit address is to ensure uniqueness of 475the node unit name at a given level of the tree. Nodes with no notion 476of address and no possible sibling of the same name (like /memory or 477/cpus) may omit the unit address in the context of this specification, 478or use the "@0" default unit address. The unit name is used to define 479a node "full path", which is the concatenation of all parent node 480unit names separated with "/". 481 482The root node doesn't have a defined name, and isn't required to have 483a name property either if you are using version 3 or earlier of the 484format. It also has no unit address (no @ symbol followed by a unit 485address). The root node unit name is thus an empty string. The full 486path to the root node is "/". 487 488Every node which actually represents an actual device (that is, a node 489which isn't only a virtual "container" for more nodes, like "/cpus" 490is) is also required to have a "device_type" property indicating the 491type of node . 492 493Finally, every node that can be referenced from a property in another 494node is required to have a "linux,phandle" property. Real open 495firmware implementations provide a unique "phandle" value for every 496node that the "prom_init()" trampoline code turns into 497"linux,phandle" properties. However, this is made optional if the 498flattened device tree is used directly. An example of a node 499referencing another node via "phandle" is when laying out the 500interrupt tree which will be described in a further version of this 501document. 502 503This "linux, phandle" property is a 32-bit value that uniquely 504identifies a node. You are free to use whatever values or system of 505values, internal pointers, or whatever to generate these, the only 506requirement is that every node for which you provide that property has 507a unique value for it. 508 509Here is an example of a simple device-tree. In this example, an "o" 510designates a node followed by the node unit name. Properties are 511presented with their name followed by their content. "content" 512represents an ASCII string (zero terminated) value, while <content> 513represents a 32-bit hexadecimal value. The various nodes in this 514example will be discussed in a later chapter. At this point, it is 515only meant to give you a idea of what a device-tree looks like. I have 516purposefully kept the "name" and "linux,phandle" properties which 517aren't necessary in order to give you a better idea of what the tree 518looks like in practice. 519 520 / o device-tree 521 |- name = "device-tree" 522 |- model = "MyBoardName" 523 |- compatible = "MyBoardFamilyName" 524 |- #address-cells = <2> 525 |- #size-cells = <2> 526 |- linux,phandle = <0> 527 | 528 o cpus 529 | | - name = "cpus" 530 | | - linux,phandle = <1> 531 | | - #address-cells = <1> 532 | | - #size-cells = <0> 533 | | 534 | o PowerPC,970@0 535 | |- name = "PowerPC,970" 536 | |- device_type = "cpu" 537 | |- reg = <0> 538 | |- clock-frequency = <5f5e1000> 539 | |- 64-bit 540 | |- linux,phandle = <2> 541 | 542 o memory@0 543 | |- name = "memory" 544 | |- device_type = "memory" 545 | |- reg = <00000000 00000000 00000000 20000000> 546 | |- linux,phandle = <3> 547 | 548 o chosen 549 |- name = "chosen" 550 |- bootargs = "root=/dev/sda2" 551 |- linux,phandle = <4> 552 553This tree is almost a minimal tree. It pretty much contains the 554minimal set of required nodes and properties to boot a linux kernel; 555that is, some basic model informations at the root, the CPUs, and the 556physical memory layout. It also includes misc information passed 557through /chosen, like in this example, the platform type (mandatory) 558and the kernel command line arguments (optional). 559 560The /cpus/PowerPC,970@0/64-bit property is an example of a 561property without a value. All other properties have a value. The 562significance of the #address-cells and #size-cells properties will be 563explained in chapter IV which defines precisely the required nodes and 564properties and their content. 565 566 5673) Device tree "structure" block 568 569The structure of the device tree is a linearized tree structure. The 570"OF_DT_BEGIN_NODE" token starts a new node, and the "OF_DT_END_NODE" 571ends that node definition. Child nodes are simply defined before 572"OF_DT_END_NODE" (that is nodes within the node). A 'token' is a 32 573bit value. The tree has to be "finished" with a OF_DT_END token 574 575Here's the basic structure of a single node: 576 577 * token OF_DT_BEGIN_NODE (that is 0x00000001) 578 * for version 1 to 3, this is the node full path as a zero 579 terminated string, starting with "/". For version 16 and later, 580 this is the node unit name only (or an empty string for the 581 root node) 582 * [align gap to next 4 bytes boundary] 583 * for each property: 584 * token OF_DT_PROP (that is 0x00000003) 585 * 32-bit value of property value size in bytes (or 0 if no 586 value) 587 * 32-bit value of offset in string block of property name 588 * property value data if any 589 * [align gap to next 4 bytes boundary] 590 * [child nodes if any] 591 * token OF_DT_END_NODE (that is 0x00000002) 592 593So the node content can be summarized as a start token, a full path, 594a list of properties, a list of child nodes, and an end token. Every 595child node is a full node structure itself as defined above. 596 597NOTE: The above definition requires that all property definitions for 598a particular node MUST precede any subnode definitions for that node. 599Although the structure would not be ambiguous if properties and 600subnodes were intermingled, the kernel parser requires that the 601properties come first (up until at least 2.6.22). Any tools 602manipulating a flattened tree must take care to preserve this 603constraint. 604 6054) Device tree "strings" block 606 607In order to save space, property names, which are generally redundant, 608are stored separately in the "strings" block. This block is simply the 609whole bunch of zero terminated strings for all property names 610concatenated together. The device-tree property definitions in the 611structure block will contain offset values from the beginning of the 612strings block. 613 614 615III - libfdt 616 617This library should be merged into dtc proper. 618This library should likely be worked into U-Boot and the kernel. 619