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David Gibsonc125a182006-02-01 03:05:22 -08001 Booting the Linux/ppc kernel without Open Firmware
2 --------------------------------------------------
3
David Gibsonc125a182006-02-01 03:05:22 -08004(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
Vitaly Wool28f9ec32006-11-20 16:32:39 +03008(c) 2006 MontaVista Software, Inc.
9 Flash chip node definition
David Gibsonc125a182006-02-01 03:05:22 -080010
Stuart Yoder5e1e9ba2007-06-06 04:29:14 +100011Table of Contents
12=================
13
14 I - Introduction
Grant Likelyede338f2011-04-28 14:27:23 -060015 1) Entry point for arch/arm
16 2) Entry point for arch/powerpc
17 3) Entry point for arch/x86
Stuart Yoder5e1e9ba2007-06-06 04:29:14 +100018
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
Stuart Yoder5e1e9ba2007-06-06 04:29:14 +100045
Anton Vorontsovb9e0ba82010-08-11 20:56:03 +040046 VII - Specifying interrupt information for devices
Stuart Yoder5e1e9ba2007-06-06 04:29:14 +100047 1) interrupts property
48 2) interrupt-parent property
49 3) OpenPIC Interrupt Controllers
50 4) ISA Interrupt Controllers
51
Anton Vorontsovb9e0ba82010-08-11 20:56:03 +040052 VIII - Specifying device power management information (sleep property)
Scott Wood2dff4172008-07-11 17:31:15 -050053
Stuart Yoder5e1e9ba2007-06-06 04:29:14 +100054 Appendix A - Sample SOC node for MPC8540
55
56
57Revision Information
58====================
59
David Gibsonc125a182006-02-01 03:05:22 -080060 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
Matt LaPlante5d3f0832006-11-30 05:21:10 +010086 required alignment between property size
David Gibsonc125a182006-02-01 03:05:22 -080087 and property data. The old style variable
88 alignment would make it impossible to do
89 "simple" insertion of properties using
Domen Puncer5dd60162007-03-02 21:44:45 +110090 memmove (thanks Milton for
David Gibsonc125a182006-02-01 03:05:22 -080091 noticing). Updated kernel patch as well
Matt LaPlante5d3f0832006-11-30 05:21:10 +010092 - Correct a few more alignment constraints
David Gibsonc125a182006-02-01 03:05:22 -080093 - Add a chapter about the device-tree
94 compiler and the textural representation of
95 the tree that can be "compiled" by dtc.
96
David Gibsonc125a182006-02-01 03:05:22 -080097 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)
Domen Puncer5dd60162007-03-02 21:44:45 +1100106 - Add some definitions for PCI host bridges
David Gibsonc125a182006-02-01 03:05:22 -0800107 - 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
Grant Likelycf4e5c62011-01-31 00:12:26 -0700120During the development of the Linux/ppc64 kernel, and more
David Gibsonc125a182006-02-01 03:05:22 -0800121specifically, 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
Lennert Buytenhek475fc7c2010-09-21 23:22:40 +0000128doesn't follow them properly. In addition, since the advent of the
David Gibsonc125a182006-02-01 03:05:22 -0800129arch/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
Sylvestre Ledruf65e51d2011-04-04 15:04:46 -0700142routing information and memory/IO ranges, among others. It is also
Grant Likelycf4e5c62011-01-31 00:12:26 -0700143recommended to define nodes for on chip devices and other buses that
David Gibsonc125a182006-02-01 03:05:22 -0800144don'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
Grant Likelyede338f2011-04-28 14:27:23 -06001521) 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 practise 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
David Gibsonc125a182006-02-01 03:05:22 -0800192-------------------------------
193
Grant Likelycf4e5c62011-01-31 00:12:26 -0700194 There is one single entry point to the kernel, at the start
David Gibsonc125a182006-02-01 03:05:22 -0800195 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
Domen Puncer5dd60162007-03-02 21:44:45 +1100204 bindings to powerpc. Only the 32-bit client interface
David Gibsonc125a182006-02-01 03:05:22 -0800205 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
Matt LaPlante2fe0ae72006-10-03 22:50:39 +0200237 r5 : NULL (as to differentiate with method a)
David Gibsonc125a182006-02-01 03:05:22 -0800238
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
David Gibsonc125a182006-02-01 03:05:22 -0800246 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
Grant Likelycf4e5c62011-01-31 00:12:26 -0700264 A kernel image may support multiple platforms, but only if the
Domen Puncer5dd60162007-03-02 21:44:45 +1100265 platforms feature the same core architecture. A single kernel build
David Gibsonc125a182006-02-01 03:05:22 -0800266 cannot support both configurations with Book E and configurations
267 with classic Powerpc architectures.
268
Grant Likelyede338f2011-04-28 14:27:23 -06002693) Entry point for arch/x86
Sebastian Andrzej Siewiorda6b7372011-02-22 21:07:37 +0100270-------------------------------
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.
David Gibsonc125a182006-02-01 03:05:22 -0800288
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
Grant Likelycf4e5c62011-01-31 00:12:26 -0700312 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
David Gibsonc125a182006-02-01 03:05:22 -0800314 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
Domen Puncer5dd60162007-03-02 21:44:45 +1100322 */
David Gibsonc125a182006-02-01 03:05:22 -0800323 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 */
David Gibson0e0293c2007-03-14 11:50:40 +1100331
332 /* version 17 fields below */
333 u32 size_dt_struct; /* size of the DT structure block */
David Gibsonc125a182006-02-01 03:05:22 -0800334};
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
Domen Puncer5dd60162007-03-02 21:44:45 +1100342 */
David Gibsonc125a182006-02-01 03:05:22 -0800343#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
Grant Likelycf4e5c62011-01-31 00:12:26 -0700351 from the physical base address of the device tree block.
David Gibsonc125a182006-02-01 03:05:22 -0800352
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
Domen Puncer5dd60162007-03-02 21:44:45 +1100379 of the reserved memory map. This map is a list of pairs of 64-
David Gibsonc125a182006-02-01 03:05:22 -0800380 bit integers. Each pair is a physical address and a size. The
David Gibsonc125a182006-02-01 03:05:22 -0800381 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
Domen Puncer5dd60162007-03-02 21:44:45 +1100393 should be 64-bit aligned.
David Gibsonc125a182006-02-01 03:05:22 -0800394
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
David Gibson0e0293c2007-03-14 11:50:40 +1100403 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.
David Gibsonc125a182006-02-01 03:05:22 -0800410
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
David Gibson0e0293c2007-03-14 11:50:40 +1100418 version 1 to 3, or 16 if you generate a tree of version 16 or 17
David Gibsonc125a182006-02-01 03:05:22 -0800419 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
Sylvestre Ledruf65e51d2011-04-04 15:04:46 -0700428 point (see further chapters for more information on the required
David Gibsonc125a182006-02-01 03:05:22 -0800429 device-tree contents)
430
David Gibson0e0293c2007-03-14 11:50:40 +1100431 - 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).
David Gibsonc125a182006-02-01 03:05:22 -0800442
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 ------------------------------
Grant Likelycf4e5c62011-01-31 00:12:26 -0700449 base -> | struct boot_param_header |
David Gibsonc125a182006-02-01 03:05:22 -0800450 ------------------------------
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 |
Grant Likelycf4e5c62011-01-31 00:12:26 -0700469 --- (base + totalsize)
David Gibsonc125a182006-02-01 03:05:22 -0800470
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
David Gibson0e0293c2007-03-14 11:50:40 +1100499format definition (as it is in Open Firmware). Version 16 makes it
David Gibsonc125a182006-02-01 03:05:22 -0800500optional as it can generate it from the unit name defined below.
501
Matt LaPlante2fe0ae72006-10-03 22:50:39 +0200502There is also a "unit name" that is used to differentiate nodes with
David Gibsonc125a182006-02-01 03:05:22 -0800503the same name at the same level, it is usually made of the node
Matt LaPlante2fe0ae72006-10-03 22:50:39 +0200504names, the "@" sign, and a "unit address", which definition is
David Gibsonc125a182006-02-01 03:05:22 -0800505specific 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
Grant Likelycf4e5c62011-01-31 00:12:26 -0700512The kernel generic code does not make any formal use of the
David Gibsonc125a182006-02-01 03:05:22 -0800513unit 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"
Grant Likelycf4e5c62011-01-31 00:12:26 -0700530is) is also required to have a "compatible" property indicating the
531specific hardware and an optional list of devices it is fully
532backwards compatible with.
David Gibsonc125a182006-02-01 03:05:22 -0800533
534Finally, every node that can be referenced from a property in another
Grant Likelycf4e5c62011-01-31 00:12:26 -0700535node 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
David Gibsonc125a182006-02-01 03:05:22 -0800540referencing another node via "phandle" is when laying out the
541interrupt tree which will be described in a further version of this
542document.
543
Grant Likelycf4e5c62011-01-31 00:12:26 -0700544The "phandle" property is a 32-bit value that uniquely
David Gibsonc125a182006-02-01 03:05:22 -0800545identifies 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>
Domen Puncer5dd60162007-03-02 21:44:45 +1100554represents a 32-bit hexadecimal value. The various nodes in this
David Gibsonc125a182006-02-01 03:05:22 -0800555example will be discussed in a later chapter. At this point, it is
556only meant to give you a idea of what a device-tree looks like. I have
557purposefully kept the "name" and "linux,phandle" properties which
558aren't necessary in order to give you a better idea of what the tree
559looks like in practice.
560
561 / o device-tree
562 |- name = "device-tree"
563 |- model = "MyBoardName"
564 |- compatible = "MyBoardFamilyName"
565 |- #address-cells = <2>
566 |- #size-cells = <2>
567 |- linux,phandle = <0>
568 |
569 o cpus
570 | | - name = "cpus"
571 | | - linux,phandle = <1>
572 | | - #address-cells = <1>
573 | | - #size-cells = <0>
574 | |
575 | o PowerPC,970@0
576 | |- name = "PowerPC,970"
577 | |- device_type = "cpu"
578 | |- reg = <0>
579 | |- clock-frequency = <5f5e1000>
Timur Tabi32aed2a2007-02-14 15:29:07 -0600580 | |- 64-bit
David Gibsonc125a182006-02-01 03:05:22 -0800581 | |- linux,phandle = <2>
582 |
583 o memory@0
584 | |- name = "memory"
585 | |- device_type = "memory"
586 | |- reg = <00000000 00000000 00000000 20000000>
587 | |- linux,phandle = <3>
588 |
589 o chosen
590 |- name = "chosen"
591 |- bootargs = "root=/dev/sda2"
David Gibsonc125a182006-02-01 03:05:22 -0800592 |- linux,phandle = <4>
593
594This tree is almost a minimal tree. It pretty much contains the
595minimal set of required nodes and properties to boot a linux kernel;
Sylvestre Ledruf65e51d2011-04-04 15:04:46 -0700596that is, some basic model information at the root, the CPUs, and the
David Gibsonc125a182006-02-01 03:05:22 -0800597physical memory layout. It also includes misc information passed
598through /chosen, like in this example, the platform type (mandatory)
599and the kernel command line arguments (optional).
600
Timur Tabi32aed2a2007-02-14 15:29:07 -0600601The /cpus/PowerPC,970@0/64-bit property is an example of a
David Gibsonc125a182006-02-01 03:05:22 -0800602property without a value. All other properties have a value. The
603significance of the #address-cells and #size-cells properties will be
604explained in chapter IV which defines precisely the required nodes and
605properties and their content.
606
607
6083) Device tree "structure" block
609
610The structure of the device tree is a linearized tree structure. The
611"OF_DT_BEGIN_NODE" token starts a new node, and the "OF_DT_END_NODE"
612ends that node definition. Child nodes are simply defined before
613"OF_DT_END_NODE" (that is nodes within the node). A 'token' is a 32
614bit value. The tree has to be "finished" with a OF_DT_END token
615
616Here's the basic structure of a single node:
617
618 * token OF_DT_BEGIN_NODE (that is 0x00000001)
619 * for version 1 to 3, this is the node full path as a zero
620 terminated string, starting with "/". For version 16 and later,
621 this is the node unit name only (or an empty string for the
622 root node)
623 * [align gap to next 4 bytes boundary]
624 * for each property:
625 * token OF_DT_PROP (that is 0x00000003)
Domen Puncer5dd60162007-03-02 21:44:45 +1100626 * 32-bit value of property value size in bytes (or 0 if no
627 value)
628 * 32-bit value of offset in string block of property name
David Gibsonc125a182006-02-01 03:05:22 -0800629 * property value data if any
630 * [align gap to next 4 bytes boundary]
631 * [child nodes if any]
632 * token OF_DT_END_NODE (that is 0x00000002)
633
Domen Puncer5dd60162007-03-02 21:44:45 +1100634So the node content can be summarized as a start token, a full path,
Matt LaPlante53cb4722006-10-03 22:55:17 +0200635a list of properties, a list of child nodes, and an end token. Every
David Gibsonc125a182006-02-01 03:05:22 -0800636child node is a full node structure itself as defined above.
637
David Gibsoneff2ebd2007-06-28 15:56:26 +1000638NOTE: The above definition requires that all property definitions for
639a particular node MUST precede any subnode definitions for that node.
640Although the structure would not be ambiguous if properties and
641subnodes were intermingled, the kernel parser requires that the
642properties come first (up until at least 2.6.22). Any tools
643manipulating a flattened tree must take care to preserve this
644constraint.
645
Matt LaPlante53cb4722006-10-03 22:55:17 +02006464) Device tree "strings" block
David Gibsonc125a182006-02-01 03:05:22 -0800647
648In order to save space, property names, which are generally redundant,
649are stored separately in the "strings" block. This block is simply the
650whole bunch of zero terminated strings for all property names
651concatenated together. The device-tree property definitions in the
652structure block will contain offset values from the beginning of the
653strings block.
654
655
656III - Required content of the device tree
657=========================================
658
659WARNING: All "linux,*" properties defined in this document apply only
660to a flattened device-tree. If your platform uses a real
661implementation of Open Firmware or an implementation compatible with
662the Open Firmware client interface, those properties will be created
663by the trampoline code in the kernel's prom_init() file. For example,
664that's where you'll have to add code to detect your board model and
Matt LaPlantea2ffd272006-10-03 22:49:15 +0200665set the platform number. However, when using the flattened device-tree
David Gibsonc125a182006-02-01 03:05:22 -0800666entry point, there is no prom_init() pass, and thus you have to
667provide those properties yourself.
668
669
6701) Note about cells and address representation
671----------------------------------------------
672
673The general rule is documented in the various Open Firmware
Domen Puncer5dd60162007-03-02 21:44:45 +1100674documentations. If you choose to describe a bus with the device-tree
David Gibsonc125a182006-02-01 03:05:22 -0800675and there exist an OF bus binding, then you should follow the
676specification. However, the kernel does not require every single
677device or bus to be described by the device tree.
678
679In general, the format of an address for a device is defined by the
680parent bus type, based on the #address-cells and #size-cells
Mark A. Greer5b14e5f2008-01-04 02:40:47 +1100681properties. Note that the parent's parent definitions of #address-cells
Matt LaPlanted9195882008-07-25 19:45:33 -0700682and #size-cells are not inherited so every node with children must specify
Mark A. Greer5b14e5f2008-01-04 02:40:47 +1100683them. The kernel requires the root node to have those properties defining
684addresses format for devices directly mapped on the processor bus.
David Gibsonc125a182006-02-01 03:05:22 -0800685
686Those 2 properties define 'cells' for representing an address and a
Domen Puncer5dd60162007-03-02 21:44:45 +1100687size. A "cell" is a 32-bit number. For example, if both contain 2
David Gibsonc125a182006-02-01 03:05:22 -0800688like the example tree given above, then an address and a size are both
Domen Puncer5dd60162007-03-02 21:44:45 +1100689composed of 2 cells, and each is a 64-bit number (cells are
David Gibsonc125a182006-02-01 03:05:22 -0800690concatenated and expected to be in big endian format). Another example
691is the way Apple firmware defines them, with 2 cells for an address
692and one cell for a size. Most 32-bit implementations should define
693#address-cells and #size-cells to 1, which represents a 32-bit value.
694Some 32-bit processors allow for physical addresses greater than 32
695bits; these processors should define #address-cells as 2.
696
697"reg" properties are always a tuple of the type "address size" where
698the number of cells of address and size is specified by the bus
699#address-cells and #size-cells. When a bus supports various address
700spaces and other flags relative to a given address allocation (like
701prefetchable, etc...) those flags are usually added to the top level
702bits of the physical address. For example, a PCI physical address is
703made of 3 cells, the bottom two containing the actual address itself
704while the top cell contains address space indication, flags, and pci
705bus & device numbers.
706
Grant Likelycf4e5c62011-01-31 00:12:26 -0700707For buses that support dynamic allocation, it's the accepted practice
David Gibsonc125a182006-02-01 03:05:22 -0800708to then not provide the address in "reg" (keep it 0) though while
709providing a flag indicating the address is dynamically allocated, and
710then, to provide a separate "assigned-addresses" property that
711contains the fully allocated addresses. See the PCI OF bindings for
712details.
713
714In general, a simple bus with no address space bits and no dynamic
715allocation is preferred if it reflects your hardware, as the existing
716kernel address parsing functions will work out of the box. If you
717define a bus type with a more complex address format, including things
718like address space bits, you'll have to add a bus translator to the
719prom_parse.c file of the recent kernels for your bus type.
720
Stephen Neuendorffere1fd1862007-12-04 12:08:57 +1100721The "reg" property only defines addresses and sizes (if #size-cells is
722non-0) within a given bus. In order to translate addresses upward
Domen Puncer5dd60162007-03-02 21:44:45 +1100723(that is into parent bus addresses, and possibly into CPU physical
Grant Likelycf4e5c62011-01-31 00:12:26 -0700724addresses), all buses must contain a "ranges" property. If the
David Gibsonc125a182006-02-01 03:05:22 -0800725"ranges" property is missing at a given level, it's assumed that
Stephen Neuendorffere1fd1862007-12-04 12:08:57 +1100726translation isn't possible, i.e., the registers are not visible on the
727parent bus. The format of the "ranges" property for a bus is a list
728of:
David Gibsonc125a182006-02-01 03:05:22 -0800729
730 bus address, parent bus address, size
731
732"bus address" is in the format of the bus this bus node is defining,
733that is, for a PCI bridge, it would be a PCI address. Thus, (bus
734address, size) defines a range of addresses for child devices. "parent
735bus address" is in the format of the parent bus of this bus. For
736example, for a PCI host controller, that would be a CPU address. For a
737PCI<->ISA bridge, that would be a PCI address. It defines the base
738address in the parent bus where the beginning of that range is mapped.
739
Grant Likelycf4e5c62011-01-31 00:12:26 -0700740For new 64-bit board support, I recommend either the 2/2 format or
David Gibsonc125a182006-02-01 03:05:22 -0800741Apple's 2/1 format which is slightly more compact since sizes usually
Grant Likelycf4e5c62011-01-31 00:12:26 -0700742fit in a single 32-bit word. New 32-bit board support should use a
David Gibsonc125a182006-02-01 03:05:22 -08007431/1 format, unless the processor supports physical addresses greater
744than 32-bits, in which case a 2/1 format is recommended.
745
Stephen Neuendorffere1fd1862007-12-04 12:08:57 +1100746Alternatively, the "ranges" property may be empty, indicating that the
747registers are visible on the parent bus using an identity mapping
748translation. In other words, the parent bus address space is the same
749as the child bus address space.
David Gibsonc125a182006-02-01 03:05:22 -0800750
7512) Note about "compatible" properties
752-------------------------------------
753
754These properties are optional, but recommended in devices and the root
755node. The format of a "compatible" property is a list of concatenated
756zero terminated strings. They allow a device to express its
757compatibility with a family of similar devices, in some cases,
758allowing a single driver to match against several devices regardless
759of their actual names.
760
7613) Note about "name" properties
762-------------------------------
763
764While earlier users of Open Firmware like OldWorld macintoshes tended
765to use the actual device name for the "name" property, it's nowadays
766considered a good practice to use a name that is closer to the device
Grant Likelycf4e5c62011-01-31 00:12:26 -0700767class (often equal to device_type). For example, nowadays, Ethernet
David Gibsonc125a182006-02-01 03:05:22 -0800768controllers are named "ethernet", an additional "model" property
769defining precisely the chip type/model, and "compatible" property
770defining the family in case a single driver can driver more than one
771of these chips. However, the kernel doesn't generally put any
772restriction on the "name" property; it is simply considered good
773practice to follow the standard and its evolutions as closely as
774possible.
775
776Note also that the new format version 16 makes the "name" property
777optional. If it's absent for a node, then the node's unit name is then
778used to reconstruct the name. That is, the part of the unit name
779before the "@" sign is used (or the entire unit name if no "@" sign
780is present).
781
7824) Note about node and property names and character set
783-------------------------------------------------------
784
Grant Likelycf4e5c62011-01-31 00:12:26 -0700785While Open Firmware provides more flexible usage of 8859-1, this
David Gibsonc125a182006-02-01 03:05:22 -0800786specification enforces more strict rules. Nodes and properties should
787be comprised only of ASCII characters 'a' to 'z', '0' to
788'9', ',', '.', '_', '+', '#', '?', and '-'. Node names additionally
789allow uppercase characters 'A' to 'Z' (property names should be
790lowercase. The fact that vendors like Apple don't respect this rule is
791irrelevant here). Additionally, node and property names should always
792begin with a character in the range 'a' to 'z' (or 'A' to 'Z' for node
793names).
794
795The maximum number of characters for both nodes and property names
796is 31. In the case of node names, this is only the leftmost part of
797a unit name (the pure "name" property), it doesn't include the unit
798address which can extend beyond that limit.
799
800
8015) Required nodes and properties
802--------------------------------
803 These are all that are currently required. However, it is strongly
804 recommended that you expose PCI host bridges as documented in the
Grant Likelycf4e5c62011-01-31 00:12:26 -0700805 PCI binding to Open Firmware, and your interrupt tree as documented
David Gibsonc125a182006-02-01 03:05:22 -0800806 in OF interrupt tree specification.
807
808 a) The root node
809
810 The root node requires some properties to be present:
811
812 - model : this is your board name/model
813 - #address-cells : address representation for "root" devices
814 - #size-cells: the size representation for "root" devices
David Gibsonc125a182006-02-01 03:05:22 -0800815 - compatible : the board "family" generally finds its way here,
816 for example, if you have 2 board models with a similar layout,
817 that typically get driven by the same platform code in the
Grant Likelycf4e5c62011-01-31 00:12:26 -0700818 kernel, you would specify the exact board model in the
819 compatible property followed by an entry that represents the SoC
820 model.
David Gibsonc125a182006-02-01 03:05:22 -0800821
822 The root node is also generally where you add additional properties
823 specific to your board like the serial number if any, that sort of
Matt LaPlante6c28f2c2006-10-03 22:46:31 +0200824 thing. It is recommended that if you add any "custom" property whose
David Gibsonc125a182006-02-01 03:05:22 -0800825 name may clash with standard defined ones, you prefix them with your
826 vendor name and a comma.
827
828 b) The /cpus node
829
830 This node is the parent of all individual CPU nodes. It doesn't
831 have any specific requirements, though it's generally good practice
832 to have at least:
833
834 #address-cells = <00000001>
835 #size-cells = <00000000>
836
837 This defines that the "address" for a CPU is a single cell, and has
838 no meaningful size. This is not necessary but the kernel will assume
839 that format when reading the "reg" properties of a CPU node, see
840 below
841
842 c) The /cpus/* nodes
843
844 So under /cpus, you are supposed to create a node for every CPU on
845 the machine. There is no specific restriction on the name of the
Grant Likelycf4e5c62011-01-31 00:12:26 -0700846 CPU, though it's common to call it <architecture>,<core>. For
David Gibsonc125a182006-02-01 03:05:22 -0800847 example, Apple uses PowerPC,G5 while IBM uses PowerPC,970FX.
Grant Likelycf4e5c62011-01-31 00:12:26 -0700848 However, the Generic Names convention suggests that it would be
849 better to simply use 'cpu' for each cpu node and use the compatible
850 property to identify the specific cpu core.
David Gibsonc125a182006-02-01 03:05:22 -0800851
852 Required properties:
853
854 - device_type : has to be "cpu"
Domen Puncer5dd60162007-03-02 21:44:45 +1100855 - reg : This is the physical CPU number, it's a single 32-bit cell
David Gibsonc125a182006-02-01 03:05:22 -0800856 and is also used as-is as the unit number for constructing the
857 unit name in the full path. For example, with 2 CPUs, you would
858 have the full path:
859 /cpus/PowerPC,970FX@0
860 /cpus/PowerPC,970FX@1
861 (unit addresses do not require leading zeroes)
Benjamin Herrenschmidt20474ab2007-10-28 08:49:28 +1100862 - d-cache-block-size : one cell, L1 data cache block size in bytes (*)
863 - i-cache-block-size : one cell, L1 instruction cache block size in
David Gibsonc125a182006-02-01 03:05:22 -0800864 bytes
865 - d-cache-size : one cell, size of L1 data cache in bytes
866 - i-cache-size : one cell, size of L1 instruction cache in bytes
David Gibsonc125a182006-02-01 03:05:22 -0800867
Benjamin Herrenschmidt20474ab2007-10-28 08:49:28 +1100868(*) The cache "block" size is the size on which the cache management
869instructions operate. Historically, this document used the cache
870"line" size here which is incorrect. The kernel will prefer the cache
871block size and will fallback to cache line size for backward
872compatibility.
873
David Gibsonc125a182006-02-01 03:05:22 -0800874 Recommended properties:
875
876 - timebase-frequency : a cell indicating the frequency of the
877 timebase in Hz. This is not directly used by the generic code,
878 but you are welcome to copy/paste the pSeries code for setting
879 the kernel timebase/decrementer calibration based on this
880 value.
881 - clock-frequency : a cell indicating the CPU core clock frequency
Domen Puncer5dd60162007-03-02 21:44:45 +1100882 in Hz. A new property will be defined for 64-bit values, but if
David Gibsonc125a182006-02-01 03:05:22 -0800883 your frequency is < 4Ghz, one cell is enough. Here as well as
884 for the above, the common code doesn't use that property, but
885 you are welcome to re-use the pSeries or Maple one. A future
886 kernel version might provide a common function for this.
Benjamin Herrenschmidt20474ab2007-10-28 08:49:28 +1100887 - d-cache-line-size : one cell, L1 data cache line size in bytes
888 if different from the block size
889 - i-cache-line-size : one cell, L1 instruction cache line size in
890 bytes if different from the block size
David Gibsonc125a182006-02-01 03:05:22 -0800891
892 You are welcome to add any property you find relevant to your board,
893 like some information about the mechanism used to soft-reset the
894 CPUs. For example, Apple puts the GPIO number for CPU soft reset
895 lines in there as a "soft-reset" property since they start secondary
896 CPUs by soft-resetting them.
897
898
899 d) the /memory node(s)
900
901 To define the physical memory layout of your board, you should
902 create one or more memory node(s). You can either create a single
903 node with all memory ranges in its reg property, or you can create
904 several nodes, as you wish. The unit address (@ part) used for the
905 full path is the address of the first range of memory defined by a
906 given node. If you use a single memory node, this will typically be
907 @0.
908
909 Required properties:
910
911 - device_type : has to be "memory"
912 - reg : This property contains all the physical memory ranges of
913 your board. It's a list of addresses/sizes concatenated
914 together, with the number of cells of each defined by the
915 #address-cells and #size-cells of the root node. For example,
Matt LaPlante6c28f2c2006-10-03 22:46:31 +0200916 with both of these properties being 2 like in the example given
David Gibsonc125a182006-02-01 03:05:22 -0800917 earlier, a 970 based machine with 6Gb of RAM could typically
918 have a "reg" property here that looks like:
919
920 00000000 00000000 00000000 80000000
921 00000001 00000000 00000001 00000000
922
923 That is a range starting at 0 of 0x80000000 bytes and a range
924 starting at 0x100000000 and of 0x100000000 bytes. You can see
925 that there is no memory covering the IO hole between 2Gb and
926 4Gb. Some vendors prefer splitting those ranges into smaller
927 segments, but the kernel doesn't care.
928
929 e) The /chosen node
930
Grant Likelycf4e5c62011-01-31 00:12:26 -0700931 This node is a bit "special". Normally, that's where Open Firmware
David Gibsonc125a182006-02-01 03:05:22 -0800932 puts some variable environment information, like the arguments, or
Stuart Yoderd1bff9e2007-02-19 11:25:05 -0600933 the default input/output devices.
David Gibsonc125a182006-02-01 03:05:22 -0800934
935 This specification makes a few of these mandatory, but also defines
936 some linux-specific properties that would be normally constructed by
937 the prom_init() trampoline when booting with an OF client interface,
938 but that you have to provide yourself when using the flattened format.
939
David Gibsonc125a182006-02-01 03:05:22 -0800940 Recommended properties:
941
942 - bootargs : This zero-terminated string is passed as the kernel
943 command line
944 - linux,stdout-path : This is the full path to your standard
945 console device if any. Typically, if you have serial devices on
946 your board, you may want to put the full path to the one set as
947 the default console in the firmware here, for the kernel to pick
Grant Likelycf4e5c62011-01-31 00:12:26 -0700948 it up as its own default console.
David Gibsonc125a182006-02-01 03:05:22 -0800949
950 Note that u-boot creates and fills in the chosen node for platforms
951 that use it.
952
Stuart Yoderd1bff9e2007-02-19 11:25:05 -0600953 (Note: a practice that is now obsolete was to include a property
954 under /chosen called interrupt-controller which had a phandle value
955 that pointed to the main interrupt controller)
956
David Gibsonc125a182006-02-01 03:05:22 -0800957 f) the /soc<SOCname> node
958
Grant Likelycf4e5c62011-01-31 00:12:26 -0700959 This node is used to represent a system-on-a-chip (SoC) and must be
960 present if the processor is a SoC. The top-level soc node contains
961 information that is global to all devices on the SoC. The node name
962 should contain a unit address for the SoC, which is the base address
963 of the memory-mapped register set for the SoC. The name of an SoC
David Gibsonc125a182006-02-01 03:05:22 -0800964 node should start with "soc", and the remainder of the name should
965 represent the part number for the soc. For example, the MPC8540's
966 soc node would be called "soc8540".
967
968 Required properties:
969
David Gibsonc125a182006-02-01 03:05:22 -0800970 - ranges : Should be defined as specified in 1) to describe the
Grant Likelycf4e5c62011-01-31 00:12:26 -0700971 translation of SoC addresses for memory mapped SoC registers.
972 - bus-frequency: Contains the bus frequency for the SoC node.
Becky Bruce7d4b95a2006-02-06 14:26:31 -0600973 Typically, the value of this field is filled in by the boot
Stefan Roeseefcc2da2009-04-16 15:11:54 -0600974 loader.
Grant Likelycf4e5c62011-01-31 00:12:26 -0700975 - compatible : Exact model of the SoC
Becky Bruce7d4b95a2006-02-06 14:26:31 -0600976
David Gibsonc125a182006-02-01 03:05:22 -0800977
978 Recommended properties:
979
980 - reg : This property defines the address and size of the
981 memory-mapped registers that are used for the SOC node itself.
982 It does not include the child device registers - these will be
983 defined inside each child node. The address specified in the
984 "reg" property should match the unit address of the SOC node.
985 - #address-cells : Address representation for "soc" devices. The
986 format of this field may vary depending on whether or not the
987 device registers are memory mapped. For memory mapped
988 registers, this field represents the number of cells needed to
989 represent the address of the registers. For SOCs that do not
990 use MMIO, a special address format should be defined that
991 contains enough cells to represent the required information.
992 See 1) above for more details on defining #address-cells.
993 - #size-cells : Size representation for "soc" devices
994 - #interrupt-cells : Defines the width of cells used to represent
995 interrupts. Typically this value is <2>, which includes a
996 32-bit number that represents the interrupt number, and a
997 32-bit number that represents the interrupt sense and level.
998 This field is only needed if the SOC contains an interrupt
999 controller.
1000
1001 The SOC node may contain child nodes for each SOC device that the
1002 platform uses. Nodes should not be created for devices which exist
1003 on the SOC but are not used by a particular platform. See chapter VI
Domen Puncer5dd60162007-03-02 21:44:45 +11001004 for more information on how to specify devices that are part of a SOC.
David Gibsonc125a182006-02-01 03:05:22 -08001005
1006 Example SOC node for the MPC8540:
1007
1008 soc8540@e0000000 {
1009 #address-cells = <1>;
1010 #size-cells = <1>;
1011 #interrupt-cells = <2>;
1012 device_type = "soc";
1013 ranges = <00000000 e0000000 00100000>
1014 reg = <e0000000 00003000>;
Becky Bruce7d4b95a2006-02-06 14:26:31 -06001015 bus-frequency = <0>;
David Gibsonc125a182006-02-01 03:05:22 -08001016 }
1017
1018
1019
1020IV - "dtc", the device tree compiler
1021====================================
1022
1023
1024dtc source code can be found at
Justin P. Mattock0ea6e612010-07-23 20:51:24 -07001025<http://git.jdl.com/gitweb/?p=dtc.git>
David Gibsonc125a182006-02-01 03:05:22 -08001026
1027WARNING: This version is still in early development stage; the
1028resulting device-tree "blobs" have not yet been validated with the
Lennert Buytenhek475fc7c2010-09-21 23:22:40 +00001029kernel. The current generated block lacks a useful reserve map (it will
David Gibsonc125a182006-02-01 03:05:22 -08001030be fixed to generate an empty one, it's up to the bootloader to fill
1031it up) among others. The error handling needs work, bugs are lurking,
1032etc...
1033
1034dtc basically takes a device-tree in a given format and outputs a
1035device-tree in another format. The currently supported formats are:
1036
1037 Input formats:
1038 -------------
1039
1040 - "dtb": "blob" format, that is a flattened device-tree block
1041 with
1042 header all in a binary blob.
1043 - "dts": "source" format. This is a text file containing a
1044 "source" for a device-tree. The format is defined later in this
1045 chapter.
1046 - "fs" format. This is a representation equivalent to the
1047 output of /proc/device-tree, that is nodes are directories and
1048 properties are files
1049
1050 Output formats:
1051 ---------------
1052
1053 - "dtb": "blob" format
1054 - "dts": "source" format
1055 - "asm": assembly language file. This is a file that can be
1056 sourced by gas to generate a device-tree "blob". That file can
1057 then simply be added to your Makefile. Additionally, the
Matt LaPlante6c28f2c2006-10-03 22:46:31 +02001058 assembly file exports some symbols that can be used.
David Gibsonc125a182006-02-01 03:05:22 -08001059
1060
1061The syntax of the dtc tool is
1062
1063 dtc [-I <input-format>] [-O <output-format>]
1064 [-o output-filename] [-V output_version] input_filename
1065
1066
Domen Puncer5dd60162007-03-02 21:44:45 +11001067The "output_version" defines what version of the "blob" format will be
David Gibsonc125a182006-02-01 03:05:22 -08001068generated. Supported versions are 1,2,3 and 16. The default is
1069currently version 3 but that may change in the future to version 16.
1070
1071Additionally, dtc performs various sanity checks on the tree, like the
Matt LaPlante6c28f2c2006-10-03 22:46:31 +02001072uniqueness of linux, phandle properties, validity of strings, etc...
David Gibsonc125a182006-02-01 03:05:22 -08001073
1074The format of the .dts "source" file is "C" like, supports C and C++
Matt LaPlante6c28f2c2006-10-03 22:46:31 +02001075style comments.
David Gibsonc125a182006-02-01 03:05:22 -08001076
1077/ {
1078}
1079
1080The above is the "device-tree" definition. It's the only statement
1081supported currently at the toplevel.
1082
1083/ {
1084 property1 = "string_value"; /* define a property containing a 0
1085 * terminated string
1086 */
1087
1088 property2 = <1234abcd>; /* define a property containing a
Domen Puncer5dd60162007-03-02 21:44:45 +11001089 * numerical 32-bit value (hexadecimal)
David Gibsonc125a182006-02-01 03:05:22 -08001090 */
1091
1092 property3 = <12345678 12345678 deadbeef>;
1093 /* define a property containing 3
Domen Puncer5dd60162007-03-02 21:44:45 +11001094 * numerical 32-bit values (cells) in
David Gibsonc125a182006-02-01 03:05:22 -08001095 * hexadecimal
1096 */
1097 property4 = [0a 0b 0c 0d de ea ad be ef];
1098 /* define a property whose content is
1099 * an arbitrary array of bytes
1100 */
1101
Uwe Kleine-Königb5950762010-11-01 15:38:34 -04001102 childnode@address { /* define a child node named "childnode"
David Gibsonc125a182006-02-01 03:05:22 -08001103 * whose unit name is "childnode at
1104 * address"
1105 */
1106
1107 childprop = "hello\n"; /* define a property "childprop" of
1108 * childnode (in this case, a string)
1109 */
1110 };
1111};
1112
1113Nodes can contain other nodes etc... thus defining the hierarchical
1114structure of the tree.
1115
1116Strings support common escape sequences from C: "\n", "\t", "\r",
1117"\(octal value)", "\x(hex value)".
1118
1119It is also suggested that you pipe your source file through cpp (gcc
1120preprocessor) so you can use #include's, #define for constants, etc...
1121
1122Finally, various options are planned but not yet implemented, like
1123automatic generation of phandles, labels (exported to the asm file so
1124you can point to a property content and change it easily from whatever
1125you link the device-tree with), label or path instead of numeric value
1126in some cells to "point" to a node (replaced by a phandle at compile
1127time), export of reserve map address to the asm file, ability to
1128specify reserve map content at compile time, etc...
1129
1130We may provide a .h include file with common definitions of that
1131proves useful for some properties (like building PCI properties or
1132interrupt maps) though it may be better to add a notion of struct
1133definitions to the compiler...
1134
1135
1136V - Recommendations for a bootloader
1137====================================
1138
1139
1140Here are some various ideas/recommendations that have been proposed
1141while all this has been defined and implemented.
1142
1143 - The bootloader may want to be able to use the device-tree itself
1144 and may want to manipulate it (to add/edit some properties,
1145 like physical memory size or kernel arguments). At this point, 2
1146 choices can be made. Either the bootloader works directly on the
1147 flattened format, or the bootloader has its own internal tree
1148 representation with pointers (similar to the kernel one) and
1149 re-flattens the tree when booting the kernel. The former is a bit
1150 more difficult to edit/modify, the later requires probably a bit
1151 more code to handle the tree structure. Note that the structure
1152 format has been designed so it's relatively easy to "insert"
1153 properties or nodes or delete them by just memmoving things
1154 around. It contains no internal offsets or pointers for this
1155 purpose.
1156
Matt LaPlanted6bc8ac2006-10-03 22:54:15 +02001157 - An example of code for iterating nodes & retrieving properties
David Gibsonc125a182006-02-01 03:05:22 -08001158 directly from the flattened tree format can be found in the kernel
Grant Likelycf4e5c62011-01-31 00:12:26 -07001159 file drivers/of/fdt.c. Look at the of_scan_flat_dt() function,
Matt LaPlanted6bc8ac2006-10-03 22:54:15 +02001160 its usage in early_init_devtree(), and the corresponding various
David Gibsonc125a182006-02-01 03:05:22 -08001161 early_init_dt_scan_*() callbacks. That code can be re-used in a
1162 GPL bootloader, and as the author of that code, I would be happy
Domen Puncer5dd60162007-03-02 21:44:45 +11001163 to discuss possible free licensing to any vendor who wishes to
David Gibsonc125a182006-02-01 03:05:22 -08001164 integrate all or part of this code into a non-GPL bootloader.
Grant Likelycf4e5c62011-01-31 00:12:26 -07001165 (reference needed; who is 'I' here? ---gcl Jan 31, 2011)
David Gibsonc125a182006-02-01 03:05:22 -08001166
1167
1168
1169VI - System-on-a-chip devices and nodes
1170=======================================
1171
1172Many companies are now starting to develop system-on-a-chip
Domen Puncer5dd60162007-03-02 21:44:45 +11001173processors, where the processor core (CPU) and many peripheral devices
David Gibsonc125a182006-02-01 03:05:22 -08001174exist on a single piece of silicon. For these SOCs, an SOC node
1175should be used that defines child nodes for the devices that make
1176up the SOC. While platforms are not required to use this model in
1177order to boot the kernel, it is highly encouraged that all SOC
1178implementations define as complete a flat-device-tree as possible to
1179describe the devices on the SOC. This will allow for the
1180genericization of much of the kernel code.
1181
1182
11831) Defining child nodes of an SOC
1184---------------------------------
1185
1186Each device that is part of an SOC may have its own node entry inside
1187the SOC node. For each device that is included in the SOC, the unit
1188address property represents the address offset for this device's
1189memory-mapped registers in the parent's address space. The parent's
1190address space is defined by the "ranges" property in the top-level soc
1191node. The "reg" property for each node that exists directly under the
1192SOC node should contain the address mapping from the child address space
1193to the parent SOC address space and the size of the device's
1194memory-mapped register file.
1195
1196For many devices that may exist inside an SOC, there are predefined
1197specifications for the format of the device tree node. All SOC child
1198nodes should follow these specifications, except where noted in this
1199document.
1200
1201See appendix A for an example partial SOC node definition for the
1202MPC8540.
1203
1204
Stuart Yoder27565902007-03-02 13:42:33 -060012052) Representing devices without a current OF specification
David Gibsonc125a182006-02-01 03:05:22 -08001206----------------------------------------------------------
1207
Grant Likelycf4e5c62011-01-31 00:12:26 -07001208Currently, there are many devices on SoCs that do not have a standard
1209representation defined as part of the Open Firmware specifications,
1210mainly because the boards that contain these SoCs are not currently
1211booted using Open Firmware. Binding documentation for new devices
1212should be added to the Documentation/devicetree/bindings directory.
1213That directory will expand as device tree support is added to more and
1214more SoCs.
1215
David Gibsonc125a182006-02-01 03:05:22 -08001216
Kumar Galab053dc52009-06-19 08:31:05 -05001217VII - Specifying interrupt information for devices
Stuart Yoder27565902007-03-02 13:42:33 -06001218===================================================
1219
Grant Likelycf4e5c62011-01-31 00:12:26 -07001220The device tree represents the buses and devices of a hardware
Stuart Yoder27565902007-03-02 13:42:33 -06001221system in a form similar to the physical bus topology of the
1222hardware.
1223
1224In addition, a logical 'interrupt tree' exists which represents the
1225hierarchy and routing of interrupts in the hardware.
1226
1227The interrupt tree model is fully described in the
1228document "Open Firmware Recommended Practice: Interrupt
1229Mapping Version 0.9". The document is available at:
1230<http://playground.sun.com/1275/practice>.
1231
12321) interrupts property
1233----------------------
1234
1235Devices that generate interrupts to a single interrupt controller
1236should use the conventional OF representation described in the
1237OF interrupt mapping documentation.
1238
1239Each device which generates interrupts must have an 'interrupt'
1240property. The interrupt property value is an arbitrary number of
1241of 'interrupt specifier' values which describe the interrupt or
1242interrupts for the device.
1243
1244The encoding of an interrupt specifier is determined by the
1245interrupt domain in which the device is located in the
1246interrupt tree. The root of an interrupt domain specifies in
1247its #interrupt-cells property the number of 32-bit cells
1248required to encode an interrupt specifier. See the OF interrupt
1249mapping documentation for a detailed description of domains.
1250
1251For example, the binding for the OpenPIC interrupt controller
1252specifies an #interrupt-cells value of 2 to encode the interrupt
1253number and level/sense information. All interrupt children in an
1254OpenPIC interrupt domain use 2 cells per interrupt in their interrupts
1255property.
1256
1257The PCI bus binding specifies a #interrupt-cell value of 1 to encode
1258which interrupt pin (INTA,INTB,INTC,INTD) is used.
1259
12602) interrupt-parent property
1261----------------------------
1262
1263The interrupt-parent property is specified to define an explicit
1264link between a device node and its interrupt parent in
1265the interrupt tree. The value of interrupt-parent is the
1266phandle of the parent node.
1267
Francis Galieguea33f3222010-04-23 00:08:02 +02001268If the interrupt-parent property is not defined for a node, its
Stuart Yoder27565902007-03-02 13:42:33 -06001269interrupt parent is assumed to be an ancestor in the node's
1270_device tree_ hierarchy.
1271
12723) OpenPIC Interrupt Controllers
1273--------------------------------
1274
1275OpenPIC interrupt controllers require 2 cells to encode
1276interrupt information. The first cell defines the interrupt
1277number. The second cell defines the sense and level
1278information.
1279
1280Sense and level information should be encoded as follows:
1281
1282 0 = low to high edge sensitive type enabled
1283 1 = active low level sensitive type enabled
1284 2 = active high level sensitive type enabled
1285 3 = high to low edge sensitive type enabled
1286
12874) ISA Interrupt Controllers
1288----------------------------
1289
1290ISA PIC interrupt controllers require 2 cells to encode
1291interrupt information. The first cell defines the interrupt
1292number. The second cell defines the sense and level
1293information.
1294
1295ISA PIC interrupt controllers should adhere to the ISA PIC
1296encodings listed below:
1297
1298 0 = active low level sensitive type enabled
1299 1 = active high level sensitive type enabled
1300 2 = high to low edge sensitive type enabled
1301 3 = low to high edge sensitive type enabled
1302
Kumar Galab053dc52009-06-19 08:31:05 -05001303VIII - Specifying Device Power Management Information (sleep property)
Scott Wood2dff4172008-07-11 17:31:15 -05001304===================================================================
1305
1306Devices on SOCs often have mechanisms for placing devices into low-power
1307states that are decoupled from the devices' own register blocks. Sometimes,
1308this information is more complicated than a cell-index property can
1309reasonably describe. Thus, each device controlled in such a manner
1310may contain a "sleep" property which describes these connections.
1311
1312The sleep property consists of one or more sleep resources, each of
1313which consists of a phandle to a sleep controller, followed by a
1314controller-specific sleep specifier of zero or more cells.
1315
1316The semantics of what type of low power modes are possible are defined
1317by the sleep controller. Some examples of the types of low power modes
1318that may be supported are:
1319
1320 - Dynamic: The device may be disabled or enabled at any time.
1321 - System Suspend: The device may request to be disabled or remain
1322 awake during system suspend, but will not be disabled until then.
1323 - Permanent: The device is disabled permanently (until the next hard
1324 reset).
1325
1326Some devices may share a clock domain with each other, such that they should
1327only be suspended when none of the devices are in use. Where reasonable,
1328such nodes should be placed on a virtual bus, where the bus has the sleep
1329property. If the clock domain is shared among devices that cannot be
1330reasonably grouped in this manner, then create a virtual sleep controller
1331(similar to an interrupt nexus, except that defining a standardized
1332sleep-map should wait until its necessity is demonstrated).
1333
David Gibsonc125a182006-02-01 03:05:22 -08001334Appendix A - Sample SOC node for MPC8540
1335========================================
1336
Scott Wood7e720632008-06-25 12:07:39 -05001337 soc@e0000000 {
David Gibsonc125a182006-02-01 03:05:22 -08001338 #address-cells = <1>;
1339 #size-cells = <1>;
Scott Wood7e720632008-06-25 12:07:39 -05001340 compatible = "fsl,mpc8540-ccsr", "simple-bus";
David Gibsonc125a182006-02-01 03:05:22 -08001341 device_type = "soc";
Scott Wood7e720632008-06-25 12:07:39 -05001342 ranges = <0x00000000 0xe0000000 0x00100000>
Becky Bruce7d4b95a2006-02-06 14:26:31 -06001343 bus-frequency = <0>;
Scott Wood7e720632008-06-25 12:07:39 -05001344 interrupt-parent = <&pic>;
David Gibsonc125a182006-02-01 03:05:22 -08001345
David Gibsonc125a182006-02-01 03:05:22 -08001346 ethernet@24000 {
Scott Wood2dff4172008-07-11 17:31:15 -05001347 #address-cells = <1>;
1348 #size-cells = <1>;
David Gibsonc125a182006-02-01 03:05:22 -08001349 device_type = "network";
1350 model = "TSEC";
Scott Wood2dff4172008-07-11 17:31:15 -05001351 compatible = "gianfar", "simple-bus";
Scott Wood7e720632008-06-25 12:07:39 -05001352 reg = <0x24000 0x1000>;
1353 local-mac-address = [ 00 E0 0C 00 73 00 ];
1354 interrupts = <29 2 30 2 34 2>;
1355 phy-handle = <&phy0>;
Scott Wood2dff4172008-07-11 17:31:15 -05001356 sleep = <&pmc 00000080>;
1357 ranges;
1358
1359 mdio@24520 {
Scott Wood7e720632008-06-25 12:07:39 -05001360 reg = <0x24520 0x20>;
Scott Wood2dff4172008-07-11 17:31:15 -05001361 compatible = "fsl,gianfar-mdio";
1362
Scott Wood7e720632008-06-25 12:07:39 -05001363 phy0: ethernet-phy@0 {
1364 interrupts = <5 1>;
Scott Wood2dff4172008-07-11 17:31:15 -05001365 reg = <0>;
1366 device_type = "ethernet-phy";
1367 };
1368
Scott Wood7e720632008-06-25 12:07:39 -05001369 phy1: ethernet-phy@1 {
1370 interrupts = <5 1>;
Scott Wood2dff4172008-07-11 17:31:15 -05001371 reg = <1>;
1372 device_type = "ethernet-phy";
1373 };
1374
Scott Wood7e720632008-06-25 12:07:39 -05001375 phy3: ethernet-phy@3 {
1376 interrupts = <7 1>;
Scott Wood2dff4172008-07-11 17:31:15 -05001377 reg = <3>;
1378 device_type = "ethernet-phy";
1379 };
1380 };
David Gibsonc125a182006-02-01 03:05:22 -08001381 };
1382
1383 ethernet@25000 {
David Gibsonc125a182006-02-01 03:05:22 -08001384 device_type = "network";
1385 model = "TSEC";
1386 compatible = "gianfar";
Scott Wood7e720632008-06-25 12:07:39 -05001387 reg = <0x25000 0x1000>;
1388 local-mac-address = [ 00 E0 0C 00 73 01 ];
1389 interrupts = <13 2 14 2 18 2>;
1390 phy-handle = <&phy1>;
Scott Wood2dff4172008-07-11 17:31:15 -05001391 sleep = <&pmc 00000040>;
David Gibsonc125a182006-02-01 03:05:22 -08001392 };
1393
1394 ethernet@26000 {
David Gibsonc125a182006-02-01 03:05:22 -08001395 device_type = "network";
1396 model = "FEC";
1397 compatible = "gianfar";
Scott Wood7e720632008-06-25 12:07:39 -05001398 reg = <0x26000 0x1000>;
1399 local-mac-address = [ 00 E0 0C 00 73 02 ];
1400 interrupts = <41 2>;
1401 phy-handle = <&phy3>;
Scott Wood2dff4172008-07-11 17:31:15 -05001402 sleep = <&pmc 00000020>;
David Gibsonc125a182006-02-01 03:05:22 -08001403 };
1404
1405 serial@4500 {
Scott Wood2dff4172008-07-11 17:31:15 -05001406 #address-cells = <1>;
1407 #size-cells = <1>;
1408 compatible = "fsl,mpc8540-duart", "simple-bus";
1409 sleep = <&pmc 00000002>;
1410 ranges;
1411
1412 serial@4500 {
1413 device_type = "serial";
1414 compatible = "ns16550";
Scott Wood7e720632008-06-25 12:07:39 -05001415 reg = <0x4500 0x100>;
Scott Wood2dff4172008-07-11 17:31:15 -05001416 clock-frequency = <0>;
Scott Wood7e720632008-06-25 12:07:39 -05001417 interrupts = <42 2>;
Scott Wood2dff4172008-07-11 17:31:15 -05001418 };
1419
1420 serial@4600 {
1421 device_type = "serial";
1422 compatible = "ns16550";
Scott Wood7e720632008-06-25 12:07:39 -05001423 reg = <0x4600 0x100>;
Scott Wood2dff4172008-07-11 17:31:15 -05001424 clock-frequency = <0>;
Scott Wood7e720632008-06-25 12:07:39 -05001425 interrupts = <42 2>;
Scott Wood2dff4172008-07-11 17:31:15 -05001426 };
David Gibsonc125a182006-02-01 03:05:22 -08001427 };
1428
Scott Wood7e720632008-06-25 12:07:39 -05001429 pic: pic@40000 {
David Gibsonc125a182006-02-01 03:05:22 -08001430 interrupt-controller;
1431 #address-cells = <0>;
Scott Wood7e720632008-06-25 12:07:39 -05001432 #interrupt-cells = <2>;
1433 reg = <0x40000 0x40000>;
David Gibsonc125a182006-02-01 03:05:22 -08001434 compatible = "chrp,open-pic";
1435 device_type = "open-pic";
David Gibsonc125a182006-02-01 03:05:22 -08001436 };
1437
1438 i2c@3000 {
Scott Wood7e720632008-06-25 12:07:39 -05001439 interrupts = <43 2>;
1440 reg = <0x3000 0x100>;
David Gibsonc125a182006-02-01 03:05:22 -08001441 compatible = "fsl-i2c";
1442 dfsrr;
Scott Wood2dff4172008-07-11 17:31:15 -05001443 sleep = <&pmc 00000004>;
David Gibsonc125a182006-02-01 03:05:22 -08001444 };
1445
Scott Wood2dff4172008-07-11 17:31:15 -05001446 pmc: power@e0070 {
1447 compatible = "fsl,mpc8540-pmc", "fsl,mpc8548-pmc";
Scott Wood7e720632008-06-25 12:07:39 -05001448 reg = <0xe0070 0x20>;
Scott Wood2dff4172008-07-11 17:31:15 -05001449 };
David Gibsonc125a182006-02-01 03:05:22 -08001450 };