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Based on kernel version 3.16. Page generated on 2014-08-06 21:38 EST.

1	           Booting the Linux/ppc kernel without Open Firmware
2	           --------------------------------------------------
3	
4	(c) 2005 Benjamin Herrenschmidt <benh at kernel.crashing.org>,
5	    IBM Corp.
6	(c) 2005 Becky Bruce <becky.bruce at freescale.com>,
7	    Freescale Semiconductor, FSL SOC and 32-bit additions
8	(c) 2006 MontaVista Software, Inc.
9	    Flash chip node definition
10	
11	Table of Contents
12	=================
13	
14	  I - Introduction
15	    1) Entry point for arch/arm
16	    2) Entry point for arch/powerpc
17	    3) Entry point for arch/x86
18	
19	  II - The DT block format
20	    1) Header
21	    2) Device tree generalities
22	    3) Device tree "structure" block
23	    4) Device tree "strings" block
24	
25	  III - Required content of the device tree
26	    1) Note about cells and address representation
27	    2) Note about "compatible" properties
28	    3) Note about "name" properties
29	    4) Note about node and property names and character set
30	    5) Required nodes and properties
31	      a) The root node
32	      b) The /cpus node
33	      c) The /cpus/* nodes
34	      d) the /memory node(s)
35	      e) The /chosen node
36	      f) the /soc<SOCname> node
37	
38	  IV - "dtc", the device tree compiler
39	
40	  V - Recommendations for a bootloader
41	
42	  VI - System-on-a-chip devices and nodes
43	    1) Defining child nodes of an SOC
44	    2) Representing devices without a current OF specification
45	
46	  VII - Specifying interrupt information for devices
47	    1) interrupts property
48	    2) interrupt-parent property
49	    3) OpenPIC Interrupt Controllers
50	    4) ISA Interrupt Controllers
51	
52	  VIII - Specifying device power management information (sleep property)
53	
54	  Appendix A - Sample SOC node for MPC8540
55	
56	
57	Revision Information
58	====================
59	
60	   May 18, 2005: Rev 0.1 - Initial draft, no chapter III yet.
61	
62	   May 19, 2005: Rev 0.2 - Add chapter III and bits & pieces here or
63	                           clarifies the fact that a lot of things are
64	                           optional, the kernel only requires a very
65	                           small device tree, though it is encouraged
66	                           to provide an as complete one as possible.
67	
68	   May 24, 2005: Rev 0.3 - Precise that DT block has to be in RAM
69				 - Misc fixes
70				 - Define version 3 and new format version 16
71				   for the DT block (version 16 needs kernel
72				   patches, will be fwd separately).
73				   String block now has a size, and full path
74				   is replaced by unit name for more
75				   compactness.
76				   linux,phandle is made optional, only nodes
77				   that are referenced by other nodes need it.
78				   "name" property is now automatically
79				   deduced from the unit name
80	
81	   June 1, 2005: Rev 0.4 - Correct confusion between OF_DT_END and
82	                           OF_DT_END_NODE in structure definition.
83	                         - Change version 16 format to always align
84	                           property data to 4 bytes. Since tokens are
85	                           already aligned, that means no specific
86	                           required alignment between property size
87	                           and property data. The old style variable
88	                           alignment would make it impossible to do
89	                           "simple" insertion of properties using
90	                           memmove (thanks Milton for
91	                           noticing). Updated kernel patch as well
92				 - Correct a few more alignment constraints
93				 - Add a chapter about the device-tree
94	                           compiler and the textural representation of
95	                           the tree that can be "compiled" by dtc.
96	
97	   November 21, 2005: Rev 0.5
98				 - Additions/generalizations for 32-bit
99				 - Changed to reflect the new arch/powerpc
100				   structure
101				 - Added chapter VI
102	
103	
104	 ToDo:
105		- Add some definitions of interrupt tree (simple/complex)
106		- Add some definitions for PCI host bridges
107		- Add some common address format examples
108		- Add definitions for standard properties and "compatible"
109		  names for cells that are not already defined by the existing
110		  OF spec.
111		- Compare FSL SOC use of PCI to standard and make sure no new
112		  node definition required.
113		- Add more information about node definitions for SOC devices
114	  	  that currently have no standard, like the FSL CPM.
115	
116	
117	I - Introduction
118	================
119	
120	During the development of the Linux/ppc64 kernel, and more
121	specifically, the addition of new platform types outside of the old
122	IBM pSeries/iSeries pair, it was decided to enforce some strict rules
123	regarding the kernel entry and bootloader <-> kernel interfaces, in
124	order to avoid the degeneration that had become the ppc32 kernel entry
125	point and the way a new platform should be added to the kernel. The
126	legacy iSeries platform breaks those rules as it predates this scheme,
127	but no new board support will be accepted in the main tree that
128	doesn't follow them properly.  In addition, since the advent of the
129	arch/powerpc merged architecture for ppc32 and ppc64, new 32-bit
130	platforms and 32-bit platforms which move into arch/powerpc will be
131	required to use these rules as well.
132	
133	The main requirement that will be defined in more detail below is
134	the presence of a device-tree whose format is defined after Open
135	Firmware specification. However, in order to make life easier
136	to embedded board vendors, the kernel doesn't require the device-tree
137	to represent every device in the system and only requires some nodes
138	and properties to be present. This will be described in detail in
139	section III, but, for example, the kernel does not require you to
140	create a node for every PCI device in the system. It is a requirement
141	to have a node for PCI host bridges in order to provide interrupt
142	routing information and memory/IO ranges, among others. It is also
143	recommended to define nodes for on chip devices and other buses that
144	don't specifically fit in an existing OF specification. This creates a
145	great flexibility in the way the kernel can then probe those and match
146	drivers to device, without having to hard code all sorts of tables. It
147	also makes it more flexible for board vendors to do minor hardware
148	upgrades without significantly impacting the kernel code or cluttering
149	it with special cases.
150	
151	
152	1) Entry point for arch/arm
153	---------------------------
154	
155	   There is one single entry point to the kernel, at the start
156	   of the kernel image. That entry point supports two calling
157	   conventions.  A summary of the interface is described here.  A full
158	   description of the boot requirements is documented in
159	   Documentation/arm/Booting
160	
161	        a) ATAGS interface.  Minimal information is passed from firmware
162	        to the kernel with a tagged list of predefined parameters.
163	
164	                r0 : 0
165	
166	                r1 : Machine type number
167	
168	                r2 : Physical address of tagged list in system RAM
169	
170	        b) Entry with a flattened device-tree block.  Firmware loads the
171	        physical address of the flattened device tree block (dtb) into r2,
172	        r1 is not used, but it is considered good practice to use a valid
173	        machine number as described in Documentation/arm/Booting.
174	
175	                r0 : 0
176	
177	                r1 : Valid machine type number.  When using a device tree,
178	                a single machine type number will often be assigned to
179	                represent a class or family of SoCs.
180	
181	                r2 : physical pointer to the device-tree block
182	                (defined in chapter II) in RAM.  Device tree can be located
183	                anywhere in system RAM, but it should be aligned on a 64 bit
184	                boundary.
185	
186	   The kernel will differentiate between ATAGS and device tree booting by
187	   reading the memory pointed to by r2 and looking for either the flattened
188	   device tree block magic value (0xd00dfeed) or the ATAG_CORE value at
189	   offset 0x4 from r2 (0x54410001).
190	
191	2) Entry point for arch/powerpc
192	-------------------------------
193	
194	   There is one single entry point to the kernel, at the start
195	   of the kernel image. That entry point supports two calling
196	   conventions:
197	
198	        a) Boot from Open Firmware. If your firmware is compatible
199	        with Open Firmware (IEEE 1275) or provides an OF compatible
200	        client interface API (support for "interpret" callback of
201	        forth words isn't required), you can enter the kernel with:
202	
203	              r5 : OF callback pointer as defined by IEEE 1275
204	              bindings to powerpc. Only the 32-bit client interface
205	              is currently supported
206	
207	              r3, r4 : address & length of an initrd if any or 0
208	
209	              The MMU is either on or off; the kernel will run the
210	              trampoline located in arch/powerpc/kernel/prom_init.c to
211	              extract the device-tree and other information from open
212	              firmware and build a flattened device-tree as described
213	              in b). prom_init() will then re-enter the kernel using
214	              the second method. This trampoline code runs in the
215	              context of the firmware, which is supposed to handle all
216	              exceptions during that time.
217	
218	        b) Direct entry with a flattened device-tree block. This entry
219	        point is called by a) after the OF trampoline and can also be
220	        called directly by a bootloader that does not support the Open
221	        Firmware client interface. It is also used by "kexec" to
222	        implement "hot" booting of a new kernel from a previous
223	        running one. This method is what I will describe in more
224	        details in this document, as method a) is simply standard Open
225	        Firmware, and thus should be implemented according to the
226	        various standard documents defining it and its binding to the
227	        PowerPC platform. The entry point definition then becomes:
228	
229	                r3 : physical pointer to the device-tree block
230	                (defined in chapter II) in RAM
231	
232	                r4 : physical pointer to the kernel itself. This is
233	                used by the assembly code to properly disable the MMU
234	                in case you are entering the kernel with MMU enabled
235	                and a non-1:1 mapping.
236	
237	                r5 : NULL (as to differentiate with method a)
238	
239	        Note about SMP entry: Either your firmware puts your other
240	        CPUs in some sleep loop or spin loop in ROM where you can get
241	        them out via a soft reset or some other means, in which case
242	        you don't need to care, or you'll have to enter the kernel
243	        with all CPUs. The way to do that with method b) will be
244	        described in a later revision of this document.
245	
246	   Board supports (platforms) are not exclusive config options. An
247	   arbitrary set of board supports can be built in a single kernel
248	   image. The kernel will "know" what set of functions to use for a
249	   given platform based on the content of the device-tree. Thus, you
250	   should:
251	
252	        a) add your platform support as a _boolean_ option in
253	        arch/powerpc/Kconfig, following the example of PPC_PSERIES,
254	        PPC_PMAC and PPC_MAPLE. The later is probably a good
255	        example of a board support to start from.
256	
257	        b) create your main platform file as
258	        "arch/powerpc/platforms/myplatform/myboard_setup.c" and add it
259	        to the Makefile under the condition of your CONFIG_
260	        option. This file will define a structure of type "ppc_md"
261	        containing the various callbacks that the generic code will
262	        use to get to your platform specific code
263	
264	  A kernel image may support multiple platforms, but only if the
265	  platforms feature the same core architecture.  A single kernel build
266	  cannot support both configurations with Book E and configurations
267	  with classic Powerpc architectures.
268	
269	3) Entry point for arch/x86
270	-------------------------------
271	
272	  There is one single 32bit entry point to the kernel at code32_start,
273	  the decompressor (the real mode entry point goes to the same  32bit
274	  entry point once it switched into protected mode). That entry point
275	  supports one calling convention which is documented in
276	  Documentation/x86/boot.txt
277	  The physical pointer to the device-tree block (defined in chapter II)
278	  is passed via setup_data which requires at least boot protocol 2.09.
279	  The type filed is defined as
280	
281	  #define SETUP_DTB                      2
282	
283	  This device-tree is used as an extension to the "boot page". As such it
284	  does not parse / consider data which is already covered by the boot
285	  page. This includes memory size, reserved ranges, command line arguments
286	  or initrd address. It simply holds information which can not be retrieved
287	  otherwise like interrupt routing or a list of devices behind an I2C bus.
288	
289	II - The DT block format
290	========================
291	
292	
293	This chapter defines the actual format of the flattened device-tree
294	passed to the kernel. The actual content of it and kernel requirements
295	are described later. You can find example of code manipulating that
296	format in various places, including arch/powerpc/kernel/prom_init.c
297	which will generate a flattened device-tree from the Open Firmware
298	representation, or the fs2dt utility which is part of the kexec tools
299	which will generate one from a filesystem representation. It is
300	expected that a bootloader like uboot provides a bit more support,
301	that will be discussed later as well.
302	
303	Note: The block has to be in main memory. It has to be accessible in
304	both real mode and virtual mode with no mapping other than main
305	memory. If you are writing a simple flash bootloader, it should copy
306	the block to RAM before passing it to the kernel.
307	
308	
309	1) Header
310	---------
311	
312	   The kernel is passed the physical address pointing to an area of memory
313	   that is roughly described in include/linux/of_fdt.h by the structure
314	   boot_param_header:
315	
316	struct boot_param_header {
317	        u32     magic;                  /* magic word OF_DT_HEADER */
318	        u32     totalsize;              /* total size of DT block */
319	        u32     off_dt_struct;          /* offset to structure */
320	        u32     off_dt_strings;         /* offset to strings */
321	        u32     off_mem_rsvmap;         /* offset to memory reserve map
322	                                           */
323	        u32     version;                /* format version */
324	        u32     last_comp_version;      /* last compatible version */
325	
326	        /* version 2 fields below */
327	        u32     boot_cpuid_phys;        /* Which physical CPU id we're
328	                                           booting on */
329	        /* version 3 fields below */
330	        u32     size_dt_strings;        /* size of the strings block */
331	
332	        /* version 17 fields below */
333	        u32	size_dt_struct;		/* size of the DT structure block */
334	};
335	
336	   Along with the constants:
337	
338	/* Definitions used by the flattened device tree */
339	#define OF_DT_HEADER            0xd00dfeed      /* 4: version,
340							   4: total size */
341	#define OF_DT_BEGIN_NODE        0x1             /* Start node: full name
342							   */
343	#define OF_DT_END_NODE          0x2             /* End node */
344	#define OF_DT_PROP              0x3             /* Property: name off,
345	                                                   size, content */
346	#define OF_DT_END               0x9
347	
348	   All values in this header are in big endian format, the various
349	   fields in this header are defined more precisely below. All
350	   "offset" values are in bytes from the start of the header; that is
351	   from the physical base address of the device tree block.
352	
353	   - magic
354	
355	     This is a magic value that "marks" the beginning of the
356	     device-tree block header. It contains the value 0xd00dfeed and is
357	     defined by the constant OF_DT_HEADER
358	
359	   - totalsize
360	
361	     This is the total size of the DT block including the header. The
362	     "DT" block should enclose all data structures defined in this
363	     chapter (who are pointed to by offsets in this header). That is,
364	     the device-tree structure, strings, and the memory reserve map.
365	
366	   - off_dt_struct
367	
368	     This is an offset from the beginning of the header to the start
369	     of the "structure" part the device tree. (see 2) device tree)
370	
371	   - off_dt_strings
372	
373	     This is an offset from the beginning of the header to the start
374	     of the "strings" part of the device-tree
375	
376	   - off_mem_rsvmap
377	
378	     This is an offset from the beginning of the header to the start
379	     of the reserved memory map. This map is a list of pairs of 64-
380	     bit integers. Each pair is a physical address and a size. The
381	     list is terminated by an entry of size 0. This map provides the
382	     kernel with a list of physical memory areas that are "reserved"
383	     and thus not to be used for memory allocations, especially during
384	     early initialization. The kernel needs to allocate memory during
385	     boot for things like un-flattening the device-tree, allocating an
386	     MMU hash table, etc... Those allocations must be done in such a
387	     way to avoid overriding critical things like, on Open Firmware
388	     capable machines, the RTAS instance, or on some pSeries, the TCE
389	     tables used for the iommu. Typically, the reserve map should
390	     contain _at least_ this DT block itself (header,total_size). If
391	     you are passing an initrd to the kernel, you should reserve it as
392	     well. You do not need to reserve the kernel image itself. The map
393	     should be 64-bit aligned.
394	
395	   - version
396	
397	     This is the version of this structure. Version 1 stops
398	     here. Version 2 adds an additional field boot_cpuid_phys.
399	     Version 3 adds the size of the strings block, allowing the kernel
400	     to reallocate it easily at boot and free up the unused flattened
401	     structure after expansion. Version 16 introduces a new more
402	     "compact" format for the tree itself that is however not backward
403	     compatible. Version 17 adds an additional field, size_dt_struct,
404	     allowing it to be reallocated or moved more easily (this is
405	     particularly useful for bootloaders which need to make
406	     adjustments to a device tree based on probed information). You
407	     should always generate a structure of the highest version defined
408	     at the time of your implementation. Currently that is version 17,
409	     unless you explicitly aim at being backward compatible.
410	
411	   - last_comp_version
412	
413	     Last compatible version. This indicates down to what version of
414	     the DT block you are backward compatible. For example, version 2
415	     is backward compatible with version 1 (that is, a kernel build
416	     for version 1 will be able to boot with a version 2 format). You
417	     should put a 1 in this field if you generate a device tree of
418	     version 1 to 3, or 16 if you generate a tree of version 16 or 17
419	     using the new unit name format.
420	
421	   - boot_cpuid_phys
422	
423	     This field only exist on version 2 headers. It indicate which
424	     physical CPU ID is calling the kernel entry point. This is used,
425	     among others, by kexec. If you are on an SMP system, this value
426	     should match the content of the "reg" property of the CPU node in
427	     the device-tree corresponding to the CPU calling the kernel entry
428	     point (see further chapters for more information on the required
429	     device-tree contents)
430	
431	   - size_dt_strings
432	
433	     This field only exists on version 3 and later headers.  It
434	     gives the size of the "strings" section of the device tree (which
435	     starts at the offset given by off_dt_strings).
436	
437	   - size_dt_struct
438	
439	     This field only exists on version 17 and later headers.  It gives
440	     the size of the "structure" section of the device tree (which
441	     starts at the offset given by off_dt_struct).
442	
443	   So the typical layout of a DT block (though the various parts don't
444	   need to be in that order) looks like this (addresses go from top to
445	   bottom):
446	
447	
448	             ------------------------------
449	     base -> |  struct boot_param_header  |
450	             ------------------------------
451	             |      (alignment gap) (*)   |
452	             ------------------------------
453	             |      memory reserve map    |
454	             ------------------------------
455	             |      (alignment gap)       |
456	             ------------------------------
457	             |                            |
458	             |    device-tree structure   |
459	             |                            |
460	             ------------------------------
461	             |      (alignment gap)       |
462	             ------------------------------
463	             |                            |
464	             |     device-tree strings    |
465	             |                            |
466	      -----> ------------------------------
467	      |
468	      |
469	      --- (base + totalsize)
470	
471	  (*) The alignment gaps are not necessarily present; their presence
472	      and size are dependent on the various alignment requirements of
473	      the individual data blocks.
474	
475	
476	2) Device tree generalities
477	---------------------------
478	
479	This device-tree itself is separated in two different blocks, a
480	structure block and a strings block. Both need to be aligned to a 4
481	byte boundary.
482	
483	First, let's quickly describe the device-tree concept before detailing
484	the storage format. This chapter does _not_ describe the detail of the
485	required types of nodes & properties for the kernel, this is done
486	later in chapter III.
487	
488	The device-tree layout is strongly inherited from the definition of
489	the Open Firmware IEEE 1275 device-tree. It's basically a tree of
490	nodes, each node having two or more named properties. A property can
491	have a value or not.
492	
493	It is a tree, so each node has one and only one parent except for the
494	root node who has no parent.
495	
496	A node has 2 names. The actual node name is generally contained in a
497	property of type "name" in the node property list whose value is a
498	zero terminated string and is mandatory for version 1 to 3 of the
499	format definition (as it is in Open Firmware). Version 16 makes it
500	optional as it can generate it from the unit name defined below.
501	
502	There is also a "unit name" that is used to differentiate nodes with
503	the same name at the same level, it is usually made of the node
504	names, the "@" sign, and a "unit address", which definition is
505	specific to the bus type the node sits on.
506	
507	The unit name doesn't exist as a property per-se but is included in
508	the device-tree structure. It is typically used to represent "path" in
509	the device-tree. More details about the actual format of these will be
510	below.
511	
512	The kernel generic code does not make any formal use of the
513	unit address (though some board support code may do) so the only real
514	requirement here for the unit address is to ensure uniqueness of
515	the node unit name at a given level of the tree. Nodes with no notion
516	of 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,
518	or use the "@0" default unit address. The unit name is used to define
519	a node "full path", which is the concatenation of all parent node
520	unit names separated with "/".
521	
522	The root node doesn't have a defined name, and isn't required to have
523	a name property either if you are using version 3 or earlier of the
524	format. It also has no unit address (no @ symbol followed by a unit
525	address). The root node unit name is thus an empty string. The full
526	path to the root node is "/".
527	
528	Every node which actually represents an actual device (that is, a node
529	which isn't only a virtual "container" for more nodes, like "/cpus"
530	is) is also required to have a "compatible" property indicating the
531	specific hardware and an optional list of devices it is fully
532	backwards compatible with.
533	
534	Finally, every node that can be referenced from a property in another
535	node is required to have either a "phandle" or a "linux,phandle"
536	property. Real Open Firmware implementations provide a unique
537	"phandle" value for every node that the "prom_init()" trampoline code
538	turns into "linux,phandle" properties. However, this is made optional
539	if the flattened device tree is used directly. An example of a node
540	referencing another node via "phandle" is when laying out the
541	interrupt tree which will be described in a further version of this
542	document.
543	
544	The "phandle" property is a 32-bit value that uniquely
545	identifies a node. You are free to use whatever values or system of
546	values, internal pointers, or whatever to generate these, the only
547	requirement is that every node for which you provide that property has
548	a unique value for it.
549	
550	Here is an example of a simple device-tree. In this example, an "o"
551	designates a node followed by the node unit name. Properties are
552	presented with their name followed by their content. "content"
553	represents an ASCII string (zero terminated) value, while <content>
554	represents a 32-bit value, specified in decimal or hexadecimal (the
555	latter prefixed 0x). The various nodes in this example will be
556	discussed in a later chapter. At this point, it is only meant to give
557	you a idea of what a device-tree looks like. I have purposefully kept
558	the "name" and "linux,phandle" properties which aren't necessary in
559	order to give you a better idea of what the tree looks like in
560	practice.
561	
562	  / o device-tree
563	      |- name = "device-tree"
564	      |- model = "MyBoardName"
565	      |- compatible = "MyBoardFamilyName"
566	      |- #address-cells = <2>
567	      |- #size-cells = <2>
568	      |- linux,phandle = <0>
569	      |
570	      o cpus
571	      | | - name = "cpus"
572	      | | - linux,phandle = <1>
573	      | | - #address-cells = <1>
574	      | | - #size-cells = <0>
575	      | |
576	      | o PowerPC,970@0
577	      |   |- name = "PowerPC,970"
578	      |   |- device_type = "cpu"
579	      |   |- reg = <0>
580	      |   |- clock-frequency = <0x5f5e1000>
581	      |   |- 64-bit
582	      |   |- linux,phandle = <2>
583	      |
584	      o memory@0
585	      | |- name = "memory"
586	      | |- device_type = "memory"
587	      | |- reg = <0x00000000 0x00000000 0x00000000 0x20000000>
588	      | |- linux,phandle = <3>
589	      |
590	      o chosen
591	        |- name = "chosen"
592	        |- bootargs = "root=/dev/sda2"
593	        |- linux,phandle = <4>
594	
595	This tree is almost a minimal tree. It pretty much contains the
596	minimal set of required nodes and properties to boot a linux kernel;
597	that is, some basic model information at the root, the CPUs, and the
598	physical memory layout.  It also includes misc information passed
599	through /chosen, like in this example, the platform type (mandatory)
600	and the kernel command line arguments (optional).
601	
602	The /cpus/PowerPC,970@0/64-bit property is an example of a
603	property without a value. All other properties have a value. The
604	significance of the #address-cells and #size-cells properties will be
605	explained in chapter IV which defines precisely the required nodes and
606	properties and their content.
607	
608	
609	3) Device tree "structure" block
610	
611	The structure of the device tree is a linearized tree structure. The
612	"OF_DT_BEGIN_NODE" token starts a new node, and the "OF_DT_END_NODE"
613	ends that node definition. Child nodes are simply defined before
614	"OF_DT_END_NODE" (that is nodes within the node). A 'token' is a 32
615	bit value. The tree has to be "finished" with a OF_DT_END token
616	
617	Here's the basic structure of a single node:
618	
619	     * token OF_DT_BEGIN_NODE (that is 0x00000001)
620	     * for version 1 to 3, this is the node full path as a zero
621	       terminated string, starting with "/". For version 16 and later,
622	       this is the node unit name only (or an empty string for the
623	       root node)
624	     * [align gap to next 4 bytes boundary]
625	     * for each property:
626	        * token OF_DT_PROP (that is 0x00000003)
627	        * 32-bit value of property value size in bytes (or 0 if no
628	          value)
629	        * 32-bit value of offset in string block of property name
630	        * property value data if any
631	        * [align gap to next 4 bytes boundary]
632	     * [child nodes if any]
633	     * token OF_DT_END_NODE (that is 0x00000002)
634	
635	So the node content can be summarized as a start token, a full path,
636	a list of properties, a list of child nodes, and an end token. Every
637	child node is a full node structure itself as defined above.
638	
639	NOTE: The above definition requires that all property definitions for
640	a particular node MUST precede any subnode definitions for that node.
641	Although the structure would not be ambiguous if properties and
642	subnodes were intermingled, the kernel parser requires that the
643	properties come first (up until at least 2.6.22).  Any tools
644	manipulating a flattened tree must take care to preserve this
645	constraint.
646	
647	4) Device tree "strings" block
648	
649	In order to save space, property names, which are generally redundant,
650	are stored separately in the "strings" block. This block is simply the
651	whole bunch of zero terminated strings for all property names
652	concatenated together. The device-tree property definitions in the
653	structure block will contain offset values from the beginning of the
654	strings block.
655	
656	
657	III - Required content of the device tree
658	=========================================
659	
660	WARNING: All "linux,*" properties defined in this document apply only
661	to a flattened device-tree. If your platform uses a real
662	implementation of Open Firmware or an implementation compatible with
663	the Open Firmware client interface, those properties will be created
664	by the trampoline code in the kernel's prom_init() file. For example,
665	that's where you'll have to add code to detect your board model and
666	set the platform number. However, when using the flattened device-tree
667	entry point, there is no prom_init() pass, and thus you have to
668	provide those properties yourself.
669	
670	
671	1) Note about cells and address representation
672	----------------------------------------------
673	
674	The general rule is documented in the various Open Firmware
675	documentations. If you choose to describe a bus with the device-tree
676	and there exist an OF bus binding, then you should follow the
677	specification. However, the kernel does not require every single
678	device or bus to be described by the device tree.
679	
680	In general, the format of an address for a device is defined by the
681	parent bus type, based on the #address-cells and #size-cells
682	properties.  Note that the parent's parent definitions of #address-cells
683	and #size-cells are not inherited so every node with children must specify
684	them.  The kernel requires the root node to have those properties defining
685	addresses format for devices directly mapped on the processor bus.
686	
687	Those 2 properties define 'cells' for representing an address and a
688	size. A "cell" is a 32-bit number. For example, if both contain 2
689	like the example tree given above, then an address and a size are both
690	composed of 2 cells, and each is a 64-bit number (cells are
691	concatenated and expected to be in big endian format). Another example
692	is the way Apple firmware defines them, with 2 cells for an address
693	and one cell for a size.  Most 32-bit implementations should define
694	#address-cells and #size-cells to 1, which represents a 32-bit value.
695	Some 32-bit processors allow for physical addresses greater than 32
696	bits; these processors should define #address-cells as 2.
697	
698	"reg" properties are always a tuple of the type "address size" where
699	the number of cells of address and size is specified by the bus
700	#address-cells and #size-cells. When a bus supports various address
701	spaces and other flags relative to a given address allocation (like
702	prefetchable, etc...) those flags are usually added to the top level
703	bits of the physical address. For example, a PCI physical address is
704	made of 3 cells, the bottom two containing the actual address itself
705	while the top cell contains address space indication, flags, and pci
706	bus & device numbers.
707	
708	For buses that support dynamic allocation, it's the accepted practice
709	to then not provide the address in "reg" (keep it 0) though while
710	providing a flag indicating the address is dynamically allocated, and
711	then, to provide a separate "assigned-addresses" property that
712	contains the fully allocated addresses. See the PCI OF bindings for
713	details.
714	
715	In general, a simple bus with no address space bits and no dynamic
716	allocation is preferred if it reflects your hardware, as the existing
717	kernel address parsing functions will work out of the box. If you
718	define a bus type with a more complex address format, including things
719	like address space bits, you'll have to add a bus translator to the
720	prom_parse.c file of the recent kernels for your bus type.
721	
722	The "reg" property only defines addresses and sizes (if #size-cells is
723	non-0) within a given bus. In order to translate addresses upward
724	(that is into parent bus addresses, and possibly into CPU physical
725	addresses), all buses must contain a "ranges" property. If the
726	"ranges" property is missing at a given level, it's assumed that
727	translation isn't possible, i.e., the registers are not visible on the
728	parent bus.  The format of the "ranges" property for a bus is a list
729	of:
730	
731		bus address, parent bus address, size
732	
733	"bus address" is in the format of the bus this bus node is defining,
734	that is, for a PCI bridge, it would be a PCI address. Thus, (bus
735	address, size) defines a range of addresses for child devices. "parent
736	bus address" is in the format of the parent bus of this bus. For
737	example, for a PCI host controller, that would be a CPU address. For a
738	PCI<->ISA bridge, that would be a PCI address. It defines the base
739	address in the parent bus where the beginning of that range is mapped.
740	
741	For new 64-bit board support, I recommend either the 2/2 format or
742	Apple's 2/1 format which is slightly more compact since sizes usually
743	fit in a single 32-bit word.   New 32-bit board support should use a
744	1/1 format, unless the processor supports physical addresses greater
745	than 32-bits, in which case a 2/1 format is recommended.
746	
747	Alternatively, the "ranges" property may be empty, indicating that the
748	registers are visible on the parent bus using an identity mapping
749	translation.  In other words, the parent bus address space is the same
750	as the child bus address space.
751	
752	2) Note about "compatible" properties
753	-------------------------------------
754	
755	These properties are optional, but recommended in devices and the root
756	node. The format of a "compatible" property is a list of concatenated
757	zero terminated strings. They allow a device to express its
758	compatibility with a family of similar devices, in some cases,
759	allowing a single driver to match against several devices regardless
760	of their actual names.
761	
762	3) Note about "name" properties
763	-------------------------------
764	
765	While earlier users of Open Firmware like OldWorld macintoshes tended
766	to use the actual device name for the "name" property, it's nowadays
767	considered a good practice to use a name that is closer to the device
768	class (often equal to device_type). For example, nowadays, Ethernet
769	controllers are named "ethernet", an additional "model" property
770	defining precisely the chip type/model, and "compatible" property
771	defining the family in case a single driver can driver more than one
772	of these chips. However, the kernel doesn't generally put any
773	restriction on the "name" property; it is simply considered good
774	practice to follow the standard and its evolutions as closely as
775	possible.
776	
777	Note also that the new format version 16 makes the "name" property
778	optional. If it's absent for a node, then the node's unit name is then
779	used to reconstruct the name. That is, the part of the unit name
780	before the "@" sign is used (or the entire unit name if no "@" sign
781	is present).
782	
783	4) Note about node and property names and character set
784	-------------------------------------------------------
785	
786	While Open Firmware provides more flexible usage of 8859-1, this
787	specification enforces more strict rules. Nodes and properties should
788	be comprised only of ASCII characters 'a' to 'z', '0' to
789	'9', ',', '.', '_', '+', '#', '?', and '-'. Node names additionally
790	allow uppercase characters 'A' to 'Z' (property names should be
791	lowercase. The fact that vendors like Apple don't respect this rule is
792	irrelevant here). Additionally, node and property names should always
793	begin with a character in the range 'a' to 'z' (or 'A' to 'Z' for node
794	names).
795	
796	The maximum number of characters for both nodes and property names
797	is 31. In the case of node names, this is only the leftmost part of
798	a unit name (the pure "name" property), it doesn't include the unit
799	address which can extend beyond that limit.
800	
801	
802	5) Required nodes and properties
803	--------------------------------
804	  These are all that are currently required. However, it is strongly
805	  recommended that you expose PCI host bridges as documented in the
806	  PCI binding to Open Firmware, and your interrupt tree as documented
807	  in OF interrupt tree specification.
808	
809	  a) The root node
810	
811	  The root node requires some properties to be present:
812	
813	    - model : this is your board name/model
814	    - #address-cells : address representation for "root" devices
815	    - #size-cells: the size representation for "root" devices
816	    - compatible : the board "family" generally finds its way here,
817	      for example, if you have 2 board models with a similar layout,
818	      that typically get driven by the same platform code in the
819	      kernel, you would specify the exact board model in the
820	      compatible property followed by an entry that represents the SoC
821	      model.
822	
823	  The root node is also generally where you add additional properties
824	  specific to your board like the serial number if any, that sort of
825	  thing. It is recommended that if you add any "custom" property whose
826	  name may clash with standard defined ones, you prefix them with your
827	  vendor name and a comma.
828	
829	  b) The /cpus node
830	
831	  This node is the parent of all individual CPU nodes. It doesn't
832	  have any specific requirements, though it's generally good practice
833	  to have at least:
834	
835	               #address-cells = <00000001>
836	               #size-cells    = <00000000>
837	
838	  This defines that the "address" for a CPU is a single cell, and has
839	  no meaningful size. This is not necessary but the kernel will assume
840	  that format when reading the "reg" properties of a CPU node, see
841	  below
842	
843	  c) The /cpus/* nodes
844	
845	  So under /cpus, you are supposed to create a node for every CPU on
846	  the machine. There is no specific restriction on the name of the
847	  CPU, though it's common to call it <architecture>,<core>. For
848	  example, Apple uses PowerPC,G5 while IBM uses PowerPC,970FX.
849	  However, the Generic Names convention suggests that it would be
850	  better to simply use 'cpu' for each cpu node and use the compatible
851	  property to identify the specific cpu core.
852	
853	  Required properties:
854	
855	    - device_type : has to be "cpu"
856	    - reg : This is the physical CPU number, it's a single 32-bit cell
857	      and is also used as-is as the unit number for constructing the
858	      unit name in the full path. For example, with 2 CPUs, you would
859	      have the full path:
860	        /cpus/PowerPC,970FX@0
861	        /cpus/PowerPC,970FX@1
862	      (unit addresses do not require leading zeroes)
863	    - d-cache-block-size : one cell, L1 data cache block size in bytes (*)
864	    - i-cache-block-size : one cell, L1 instruction cache block size in
865	      bytes
866	    - d-cache-size : one cell, size of L1 data cache in bytes
867	    - i-cache-size : one cell, size of L1 instruction cache in bytes
868	
869	(*) The cache "block" size is the size on which the cache management
870	instructions operate. Historically, this document used the cache
871	"line" size here which is incorrect. The kernel will prefer the cache
872	block size and will fallback to cache line size for backward
873	compatibility.
874	
875	  Recommended properties:
876	
877	    - timebase-frequency : a cell indicating the frequency of the
878	      timebase in Hz. This is not directly used by the generic code,
879	      but you are welcome to copy/paste the pSeries code for setting
880	      the kernel timebase/decrementer calibration based on this
881	      value.
882	    - clock-frequency : a cell indicating the CPU core clock frequency
883	      in Hz. A new property will be defined for 64-bit values, but if
884	      your frequency is < 4Ghz, one cell is enough. Here as well as
885	      for the above, the common code doesn't use that property, but
886	      you are welcome to re-use the pSeries or Maple one. A future
887	      kernel version might provide a common function for this.
888	    - d-cache-line-size : one cell, L1 data cache line size in bytes
889	      if different from the block size
890	    - i-cache-line-size : one cell, L1 instruction cache line size in
891	      bytes if different from the block size
892	
893	  You are welcome to add any property you find relevant to your board,
894	  like some information about the mechanism used to soft-reset the
895	  CPUs. For example, Apple puts the GPIO number for CPU soft reset
896	  lines in there as a "soft-reset" property since they start secondary
897	  CPUs by soft-resetting them.
898	
899	
900	  d) the /memory node(s)
901	
902	  To define the physical memory layout of your board, you should
903	  create one or more memory node(s). You can either create a single
904	  node with all memory ranges in its reg property, or you can create
905	  several nodes, as you wish. The unit address (@ part) used for the
906	  full path is the address of the first range of memory defined by a
907	  given node. If you use a single memory node, this will typically be
908	  @0.
909	
910	  Required properties:
911	
912	    - device_type : has to be "memory"
913	    - reg : This property contains all the physical memory ranges of
914	      your board. It's a list of addresses/sizes concatenated
915	      together, with the number of cells of each defined by the
916	      #address-cells and #size-cells of the root node. For example,
917	      with both of these properties being 2 like in the example given
918	      earlier, a 970 based machine with 6Gb of RAM could typically
919	      have a "reg" property here that looks like:
920	
921	      00000000 00000000 00000000 80000000
922	      00000001 00000000 00000001 00000000
923	
924	      That is a range starting at 0 of 0x80000000 bytes and a range
925	      starting at 0x100000000 and of 0x100000000 bytes. You can see
926	      that there is no memory covering the IO hole between 2Gb and
927	      4Gb. Some vendors prefer splitting those ranges into smaller
928	      segments, but the kernel doesn't care.
929	
930	  e) The /chosen node
931	
932	  This node is a bit "special". Normally, that's where Open Firmware
933	  puts some variable environment information, like the arguments, or
934	  the default input/output devices.
935	
936	  This specification makes a few of these mandatory, but also defines
937	  some linux-specific properties that would be normally constructed by
938	  the prom_init() trampoline when booting with an OF client interface,
939	  but that you have to provide yourself when using the flattened format.
940	
941	  Recommended properties:
942	
943	    - bootargs : This zero-terminated string is passed as the kernel
944	      command line
945	    - linux,stdout-path : This is the full path to your standard
946	      console device if any. Typically, if you have serial devices on
947	      your board, you may want to put the full path to the one set as
948	      the default console in the firmware here, for the kernel to pick
949	      it up as its own default console.
950	
951	  Note that u-boot creates and fills in the chosen node for platforms
952	  that use it.
953	
954	  (Note: a practice that is now obsolete was to include a property
955	  under /chosen called interrupt-controller which had a phandle value
956	  that pointed to the main interrupt controller)
957	
958	  f) the /soc<SOCname> node
959	
960	  This node is used to represent a system-on-a-chip (SoC) and must be
961	  present if the processor is a SoC. The top-level soc node contains
962	  information that is global to all devices on the SoC. The node name
963	  should contain a unit address for the SoC, which is the base address
964	  of the memory-mapped register set for the SoC. The name of an SoC
965	  node should start with "soc", and the remainder of the name should
966	  represent the part number for the soc.  For example, the MPC8540's
967	  soc node would be called "soc8540".
968	
969	  Required properties:
970	
971	    - ranges : Should be defined as specified in 1) to describe the
972	      translation of SoC addresses for memory mapped SoC registers.
973	    - bus-frequency: Contains the bus frequency for the SoC node.
974	      Typically, the value of this field is filled in by the boot
975	      loader.
976	    - compatible : Exact model of the SoC
977	
978	
979	  Recommended properties:
980	
981	    - reg : This property defines the address and size of the
982	      memory-mapped registers that are used for the SOC node itself.
983	      It does not include the child device registers - these will be
984	      defined inside each child node.  The address specified in the
985	      "reg" property should match the unit address of the SOC node.
986	    - #address-cells : Address representation for "soc" devices.  The
987	      format of this field may vary depending on whether or not the
988	      device registers are memory mapped.  For memory mapped
989	      registers, this field represents the number of cells needed to
990	      represent the address of the registers.  For SOCs that do not
991	      use MMIO, a special address format should be defined that
992	      contains enough cells to represent the required information.
993	      See 1) above for more details on defining #address-cells.
994	    - #size-cells : Size representation for "soc" devices
995	    - #interrupt-cells : Defines the width of cells used to represent
996	       interrupts.  Typically this value is <2>, which includes a
997	       32-bit number that represents the interrupt number, and a
998	       32-bit number that represents the interrupt sense and level.
999	       This field is only needed if the SOC contains an interrupt
1000	       controller.
1001	
1002	  The SOC node may contain child nodes for each SOC device that the
1003	  platform uses.  Nodes should not be created for devices which exist
1004	  on the SOC but are not used by a particular platform. See chapter VI
1005	  for more information on how to specify devices that are part of a SOC.
1006	
1007	  Example SOC node for the MPC8540:
1008	
1009		soc8540@e0000000 {
1010			#address-cells = <1>;
1011			#size-cells = <1>;
1012			#interrupt-cells = <2>;
1013			device_type = "soc";
1014			ranges = <0x00000000 0xe0000000 0x00100000>
1015			reg = <0xe0000000 0x00003000>;
1016			bus-frequency = <0>;
1017		}
1018	
1019	
1020	
1021	IV - "dtc", the device tree compiler
1022	====================================
1023	
1024	
1025	dtc source code can be found at
1026	<http://git.jdl.com/gitweb/?p=dtc.git>
1027	
1028	WARNING: This version is still in early development stage; the
1029	resulting device-tree "blobs" have not yet been validated with the
1030	kernel. The current generated block lacks a useful reserve map (it will
1031	be fixed to generate an empty one, it's up to the bootloader to fill
1032	it up) among others. The error handling needs work, bugs are lurking,
1033	etc...
1034	
1035	dtc basically takes a device-tree in a given format and outputs a
1036	device-tree in another format. The currently supported formats are:
1037	
1038	  Input formats:
1039	  -------------
1040	
1041	     - "dtb": "blob" format, that is a flattened device-tree block
1042	       with
1043	        header all in a binary blob.
1044	     - "dts": "source" format. This is a text file containing a
1045	       "source" for a device-tree. The format is defined later in this
1046	        chapter.
1047	     - "fs" format. This is a representation equivalent to the
1048	        output of /proc/device-tree, that is nodes are directories and
1049		properties are files
1050	
1051	 Output formats:
1052	 ---------------
1053	
1054	     - "dtb": "blob" format
1055	     - "dts": "source" format
1056	     - "asm": assembly language file. This is a file that can be
1057	       sourced by gas to generate a device-tree "blob". That file can
1058	       then simply be added to your Makefile. Additionally, the
1059	       assembly file exports some symbols that can be used.
1060	
1061	
1062	The syntax of the dtc tool is
1063	
1064	    dtc [-I <input-format>] [-O <output-format>]
1065	        [-o output-filename] [-V output_version] input_filename
1066	
1067	
1068	The "output_version" defines what version of the "blob" format will be
1069	generated. Supported versions are 1,2,3 and 16. The default is
1070	currently version 3 but that may change in the future to version 16.
1071	
1072	Additionally, dtc performs various sanity checks on the tree, like the
1073	uniqueness of linux, phandle properties, validity of strings, etc...
1074	
1075	The format of the .dts "source" file is "C" like, supports C and C++
1076	style comments.
1077	
1078	/ {
1079	}
1080	
1081	The above is the "device-tree" definition. It's the only statement
1082	supported currently at the toplevel.
1083	
1084	/ {
1085	  property1 = "string_value";	/* define a property containing a 0
1086	                                 * terminated string
1087					 */
1088	
1089	  property2 = <0x1234abcd>;	/* define a property containing a
1090	                                 * numerical 32-bit value (hexadecimal)
1091					 */
1092	
1093	  property3 = <0x12345678 0x12345678 0xdeadbeef>;
1094	                                /* define a property containing 3
1095	                                 * numerical 32-bit values (cells) in
1096	                                 * hexadecimal
1097					 */
1098	  property4 = [0x0a 0x0b 0x0c 0x0d 0xde 0xea 0xad 0xbe 0xef];
1099	                                /* define a property whose content is
1100	                                 * an arbitrary array of bytes
1101	                                 */
1102	
1103	  childnode@address {	/* define a child node named "childnode"
1104	                                 * whose unit name is "childnode at
1105					 * address"
1106	                                 */
1107	
1108	    childprop = "hello\n";      /* define a property "childprop" of
1109	                                 * childnode (in this case, a string)
1110	                                 */
1111	  };
1112	};
1113	
1114	Nodes can contain other nodes etc... thus defining the hierarchical
1115	structure of the tree.
1116	
1117	Strings support common escape sequences from C: "\n", "\t", "\r",
1118	"\(octal value)", "\x(hex value)".
1119	
1120	It is also suggested that you pipe your source file through cpp (gcc
1121	preprocessor) so you can use #include's, #define for constants, etc...
1122	
1123	Finally, various options are planned but not yet implemented, like
1124	automatic generation of phandles, labels (exported to the asm file so
1125	you can point to a property content and change it easily from whatever
1126	you link the device-tree with), label or path instead of numeric value
1127	in some cells to "point" to a node (replaced by a phandle at compile
1128	time), export of reserve map address to the asm file, ability to
1129	specify reserve map content at compile time, etc...
1130	
1131	We may provide a .h include file with common definitions of that
1132	proves useful for some properties (like building PCI properties or
1133	interrupt maps) though it may be better to add a notion of struct
1134	definitions to the compiler...
1135	
1136	
1137	V - Recommendations for a bootloader
1138	====================================
1139	
1140	
1141	Here are some various ideas/recommendations that have been proposed
1142	while all this has been defined and implemented.
1143	
1144	  - The bootloader may want to be able to use the device-tree itself
1145	    and may want to manipulate it (to add/edit some properties,
1146	    like physical memory size or kernel arguments). At this point, 2
1147	    choices can be made. Either the bootloader works directly on the
1148	    flattened format, or the bootloader has its own internal tree
1149	    representation with pointers (similar to the kernel one) and
1150	    re-flattens the tree when booting the kernel. The former is a bit
1151	    more difficult to edit/modify, the later requires probably a bit
1152	    more code to handle the tree structure. Note that the structure
1153	    format has been designed so it's relatively easy to "insert"
1154	    properties or nodes or delete them by just memmoving things
1155	    around. It contains no internal offsets or pointers for this
1156	    purpose.
1157	
1158	  - An example of code for iterating nodes & retrieving properties
1159	    directly from the flattened tree format can be found in the kernel
1160	    file drivers/of/fdt.c.  Look at the of_scan_flat_dt() function,
1161	    its usage in early_init_devtree(), and the corresponding various
1162	    early_init_dt_scan_*() callbacks. That code can be re-used in a
1163	    GPL bootloader, and as the author of that code, I would be happy
1164	    to discuss possible free licensing to any vendor who wishes to
1165	    integrate all or part of this code into a non-GPL bootloader.
1166	    (reference needed; who is 'I' here? ---gcl Jan 31, 2011)
1167	
1168	
1169	
1170	VI - System-on-a-chip devices and nodes
1171	=======================================
1172	
1173	Many companies are now starting to develop system-on-a-chip
1174	processors, where the processor core (CPU) and many peripheral devices
1175	exist on a single piece of silicon.  For these SOCs, an SOC node
1176	should be used that defines child nodes for the devices that make
1177	up the SOC. While platforms are not required to use this model in
1178	order to boot the kernel, it is highly encouraged that all SOC
1179	implementations define as complete a flat-device-tree as possible to
1180	describe the devices on the SOC.  This will allow for the
1181	genericization of much of the kernel code.
1182	
1183	
1184	1) Defining child nodes of an SOC
1185	---------------------------------
1186	
1187	Each device that is part of an SOC may have its own node entry inside
1188	the SOC node.  For each device that is included in the SOC, the unit
1189	address property represents the address offset for this device's
1190	memory-mapped registers in the parent's address space.  The parent's
1191	address space is defined by the "ranges" property in the top-level soc
1192	node. The "reg" property for each node that exists directly under the
1193	SOC node should contain the address mapping from the child address space
1194	to the parent SOC address space and the size of the device's
1195	memory-mapped register file.
1196	
1197	For many devices that may exist inside an SOC, there are predefined
1198	specifications for the format of the device tree node.  All SOC child
1199	nodes should follow these specifications, except where noted in this
1200	document.
1201	
1202	See appendix A for an example partial SOC node definition for the
1203	MPC8540.
1204	
1205	
1206	2) Representing devices without a current OF specification
1207	----------------------------------------------------------
1208	
1209	Currently, there are many devices on SoCs that do not have a standard
1210	representation defined as part of the Open Firmware specifications,
1211	mainly because the boards that contain these SoCs are not currently
1212	booted using Open Firmware.  Binding documentation for new devices
1213	should be added to the Documentation/devicetree/bindings directory.
1214	That directory will expand as device tree support is added to more and
1215	more SoCs.
1216	
1217	
1218	VII - Specifying interrupt information for devices
1219	===================================================
1220	
1221	The device tree represents the buses and devices of a hardware
1222	system in a form similar to the physical bus topology of the
1223	hardware.
1224	
1225	In addition, a logical 'interrupt tree' exists which represents the
1226	hierarchy and routing of interrupts in the hardware.
1227	
1228	The interrupt tree model is fully described in the
1229	document "Open Firmware Recommended Practice: Interrupt
1230	Mapping Version 0.9".  The document is available at:
1231	<http://www.openfirmware.org/ofwg/practice/>
1232	
1233	1) interrupts property
1234	----------------------
1235	
1236	Devices that generate interrupts to a single interrupt controller
1237	should use the conventional OF representation described in the
1238	OF interrupt mapping documentation.
1239	
1240	Each device which generates interrupts must have an 'interrupt'
1241	property.  The interrupt property value is an arbitrary number of
1242	of 'interrupt specifier' values which describe the interrupt or
1243	interrupts for the device.
1244	
1245	The encoding of an interrupt specifier is determined by the
1246	interrupt domain in which the device is located in the
1247	interrupt tree.  The root of an interrupt domain specifies in
1248	its #interrupt-cells property the number of 32-bit cells
1249	required to encode an interrupt specifier.  See the OF interrupt
1250	mapping documentation for a detailed description of domains.
1251	
1252	For example, the binding for the OpenPIC interrupt controller
1253	specifies  an #interrupt-cells value of 2 to encode the interrupt
1254	number and level/sense information. All interrupt children in an
1255	OpenPIC interrupt domain use 2 cells per interrupt in their interrupts
1256	property.
1257	
1258	The PCI bus binding specifies a #interrupt-cell value of 1 to encode
1259	which interrupt pin (INTA,INTB,INTC,INTD) is used.
1260	
1261	2) interrupt-parent property
1262	----------------------------
1263	
1264	The interrupt-parent property is specified to define an explicit
1265	link between a device node and its interrupt parent in
1266	the interrupt tree.  The value of interrupt-parent is the
1267	phandle of the parent node.
1268	
1269	If the interrupt-parent property is not defined for a node, its
1270	interrupt parent is assumed to be an ancestor in the node's
1271	_device tree_ hierarchy.
1272	
1273	3) OpenPIC Interrupt Controllers
1274	--------------------------------
1275	
1276	OpenPIC interrupt controllers require 2 cells to encode
1277	interrupt information.  The first cell defines the interrupt
1278	number.  The second cell defines the sense and level
1279	information.
1280	
1281	Sense and level information should be encoded as follows:
1282	
1283		0 = low to high edge sensitive type enabled
1284		1 = active low level sensitive type enabled
1285		2 = active high level sensitive type enabled
1286		3 = high to low edge sensitive type enabled
1287	
1288	4) ISA Interrupt Controllers
1289	----------------------------
1290	
1291	ISA PIC interrupt controllers require 2 cells to encode
1292	interrupt information.  The first cell defines the interrupt
1293	number.  The second cell defines the sense and level
1294	information.
1295	
1296	ISA PIC interrupt controllers should adhere to the ISA PIC
1297	encodings listed below:
1298	
1299		0 =  active low level sensitive type enabled
1300		1 =  active high level sensitive type enabled
1301		2 =  high to low edge sensitive type enabled
1302		3 =  low to high edge sensitive type enabled
1303	
1304	VIII - Specifying Device Power Management Information (sleep property)
1305	===================================================================
1306	
1307	Devices on SOCs often have mechanisms for placing devices into low-power
1308	states that are decoupled from the devices' own register blocks.  Sometimes,
1309	this information is more complicated than a cell-index property can
1310	reasonably describe.  Thus, each device controlled in such a manner
1311	may contain a "sleep" property which describes these connections.
1312	
1313	The sleep property consists of one or more sleep resources, each of
1314	which consists of a phandle to a sleep controller, followed by a
1315	controller-specific sleep specifier of zero or more cells.
1316	
1317	The semantics of what type of low power modes are possible are defined
1318	by the sleep controller.  Some examples of the types of low power modes
1319	that may be supported are:
1320	
1321	 - Dynamic: The device may be disabled or enabled at any time.
1322	 - System Suspend: The device may request to be disabled or remain
1323	   awake during system suspend, but will not be disabled until then.
1324	 - Permanent: The device is disabled permanently (until the next hard
1325	   reset).
1326	
1327	Some devices may share a clock domain with each other, such that they should
1328	only be suspended when none of the devices are in use.  Where reasonable,
1329	such nodes should be placed on a virtual bus, where the bus has the sleep
1330	property.  If the clock domain is shared among devices that cannot be
1331	reasonably grouped in this manner, then create a virtual sleep controller
1332	(similar to an interrupt nexus, except that defining a standardized
1333	sleep-map should wait until its necessity is demonstrated).
1334	
1335	Appendix A - Sample SOC node for MPC8540
1336	========================================
1337	
1338		soc@e0000000 {
1339			#address-cells = <1>;
1340			#size-cells = <1>;
1341			compatible = "fsl,mpc8540-ccsr", "simple-bus";
1342			device_type = "soc";
1343			ranges = <0x00000000 0xe0000000 0x00100000>
1344			bus-frequency = <0>;
1345			interrupt-parent = <&pic>;
1346	
1347			ethernet@24000 {
1348				#address-cells = <1>;
1349				#size-cells = <1>;
1350				device_type = "network";
1351				model = "TSEC";
1352				compatible = "gianfar", "simple-bus";
1353				reg = <0x24000 0x1000>;
1354				local-mac-address = [ 0x00 0xE0 0x0C 0x00 0x73 0x00 ];
1355				interrupts = <0x29 2 0x30 2 0x34 2>;
1356				phy-handle = <&phy0>;
1357				sleep = <&pmc 0x00000080>;
1358				ranges;
1359	
1360				mdio@24520 {
1361					reg = <0x24520 0x20>;
1362					compatible = "fsl,gianfar-mdio";
1363	
1364					phy0: ethernet-phy@0 {
1365						interrupts = <5 1>;
1366						reg = <0>;
1367					};
1368	
1369					phy1: ethernet-phy@1 {
1370						interrupts = <5 1>;
1371						reg = <1>;
1372					};
1373	
1374					phy3: ethernet-phy@3 {
1375						interrupts = <7 1>;
1376						reg = <3>;
1377					};
1378				};
1379			};
1380	
1381			ethernet@25000 {
1382				device_type = "network";
1383				model = "TSEC";
1384				compatible = "gianfar";
1385				reg = <0x25000 0x1000>;
1386				local-mac-address = [ 0x00 0xE0 0x0C 0x00 0x73 0x01 ];
1387				interrupts = <0x13 2 0x14 2 0x18 2>;
1388				phy-handle = <&phy1>;
1389				sleep = <&pmc 0x00000040>;
1390			};
1391	
1392			ethernet@26000 {
1393				device_type = "network";
1394				model = "FEC";
1395				compatible = "gianfar";
1396				reg = <0x26000 0x1000>;
1397				local-mac-address = [ 0x00 0xE0 0x0C 0x00 0x73 0x02 ];
1398				interrupts = <0x41 2>;
1399				phy-handle = <&phy3>;
1400				sleep = <&pmc 0x00000020>;
1401			};
1402	
1403			serial@4500 {
1404				#address-cells = <1>;
1405				#size-cells = <1>;
1406				compatible = "fsl,mpc8540-duart", "simple-bus";
1407				sleep = <&pmc 0x00000002>;
1408				ranges;
1409	
1410				serial@4500 {
1411					device_type = "serial";
1412					compatible = "ns16550";
1413					reg = <0x4500 0x100>;
1414					clock-frequency = <0>;
1415					interrupts = <0x42 2>;
1416				};
1417	
1418				serial@4600 {
1419					device_type = "serial";
1420					compatible = "ns16550";
1421					reg = <0x4600 0x100>;
1422					clock-frequency = <0>;
1423					interrupts = <0x42 2>;
1424				};
1425			};
1426	
1427			pic: pic@40000 {
1428				interrupt-controller;
1429				#address-cells = <0>;
1430				#interrupt-cells = <2>;
1431				reg = <0x40000 0x40000>;
1432				compatible = "chrp,open-pic";
1433				device_type = "open-pic";
1434			};
1435	
1436			i2c@3000 {
1437				interrupts = <0x43 2>;
1438				reg = <0x3000 0x100>;
1439				compatible  = "fsl-i2c";
1440				dfsrr;
1441				sleep = <&pmc 0x00000004>;
1442			};
1443	
1444			pmc: power@e0070 {
1445				compatible = "fsl,mpc8540-pmc", "fsl,mpc8548-pmc";
1446				reg = <0xe0070 0x20>;
1447			};
1448		};
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