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1 | Booting the Linux/ppc kernel without Open Firmware |
2 | -------------------------------------------------- | |
3 | ||
c125a183 DG |
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 | |
28f9ec34 VW |
8 | (c) 2006 MontaVista Software, Inc. |
9 | Flash chip node definition | |
c125a183 | 10 | |
5e1e9ba6 SY |
11 | Table of Contents |
12 | ================= | |
13 | ||
14 | I - Introduction | |
15 | 1) Entry point for arch/powerpc | |
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16 | |
17 | II - The DT block format | |
18 | 1) Header | |
19 | 2) Device tree generalities | |
20 | 3) Device tree "structure" block | |
21 | 4) Device tree "strings" block | |
22 | ||
23 | III - Required content of the device tree | |
24 | 1) Note about cells and address representation | |
25 | 2) Note about "compatible" properties | |
26 | 3) Note about "name" properties | |
27 | 4) Note about node and property names and character set | |
28 | 5) Required nodes and properties | |
29 | a) The root node | |
30 | b) The /cpus node | |
31 | c) The /cpus/* nodes | |
32 | d) the /memory node(s) | |
33 | e) The /chosen node | |
34 | f) the /soc<SOCname> node | |
35 | ||
36 | IV - "dtc", the device tree compiler | |
37 | ||
38 | V - Recommendations for a bootloader | |
39 | ||
40 | VI - System-on-a-chip devices and nodes | |
41 | 1) Defining child nodes of an SOC | |
42 | 2) Representing devices without a current OF specification | |
5e1e9ba6 | 43 | |
b9e0ba81 | 44 | VII - Specifying interrupt information for devices |
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45 | 1) interrupts property |
46 | 2) interrupt-parent property | |
47 | 3) OpenPIC Interrupt Controllers | |
48 | 4) ISA Interrupt Controllers | |
49 | ||
b9e0ba81 | 50 | VIII - Specifying device power management information (sleep property) |
2dff4177 | 51 | |
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52 | Appendix A - Sample SOC node for MPC8540 |
53 | ||
54 | ||
55 | Revision Information | |
56 | ==================== | |
57 | ||
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58 | May 18, 2005: Rev 0.1 - Initial draft, no chapter III yet. |
59 | ||
60 | May 19, 2005: Rev 0.2 - Add chapter III and bits & pieces here or | |
61 | clarifies the fact that a lot of things are | |
62 | optional, the kernel only requires a very | |
63 | small device tree, though it is encouraged | |
64 | to provide an as complete one as possible. | |
65 | ||
66 | May 24, 2005: Rev 0.3 - Precise that DT block has to be in RAM | |
67 | - Misc fixes | |
68 | - Define version 3 and new format version 16 | |
69 | for the DT block (version 16 needs kernel | |
70 | patches, will be fwd separately). | |
71 | String block now has a size, and full path | |
72 | is replaced by unit name for more | |
73 | compactness. | |
74 | linux,phandle is made optional, only nodes | |
75 | that are referenced by other nodes need it. | |
76 | "name" property is now automatically | |
77 | deduced from the unit name | |
78 | ||
79 | June 1, 2005: Rev 0.4 - Correct confusion between OF_DT_END and | |
80 | OF_DT_END_NODE in structure definition. | |
81 | - Change version 16 format to always align | |
82 | property data to 4 bytes. Since tokens are | |
83 | already aligned, that means no specific | |
5d3f083d | 84 | required alignment between property size |
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85 | and property data. The old style variable |
86 | alignment would make it impossible to do | |
87 | "simple" insertion of properties using | |
5dd60166 | 88 | memmove (thanks Milton for |
c125a183 | 89 | noticing). Updated kernel patch as well |
5d3f083d | 90 | - Correct a few more alignment constraints |
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91 | - Add a chapter about the device-tree |
92 | compiler and the textural representation of | |
93 | the tree that can be "compiled" by dtc. | |
94 | ||
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95 | November 21, 2005: Rev 0.5 |
96 | - Additions/generalizations for 32-bit | |
97 | - Changed to reflect the new arch/powerpc | |
98 | structure | |
99 | - Added chapter VI | |
100 | ||
101 | ||
102 | ToDo: | |
103 | - Add some definitions of interrupt tree (simple/complex) | |
5dd60166 | 104 | - Add some definitions for PCI host bridges |
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105 | - Add some common address format examples |
106 | - Add definitions for standard properties and "compatible" | |
107 | names for cells that are not already defined by the existing | |
108 | OF spec. | |
109 | - Compare FSL SOC use of PCI to standard and make sure no new | |
110 | node definition required. | |
111 | - Add more information about node definitions for SOC devices | |
112 | that currently have no standard, like the FSL CPM. | |
113 | ||
114 | ||
115 | I - Introduction | |
116 | ================ | |
117 | ||
cf4e5c6e | 118 | During the development of the Linux/ppc64 kernel, and more |
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119 | specifically, the addition of new platform types outside of the old |
120 | IBM pSeries/iSeries pair, it was decided to enforce some strict rules | |
121 | regarding the kernel entry and bootloader <-> kernel interfaces, in | |
122 | order to avoid the degeneration that had become the ppc32 kernel entry | |
123 | point and the way a new platform should be added to the kernel. The | |
124 | legacy iSeries platform breaks those rules as it predates this scheme, | |
125 | but no new board support will be accepted in the main tree that | |
475fc7c0 | 126 | doesn't follow them properly. In addition, since the advent of the |
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127 | arch/powerpc merged architecture for ppc32 and ppc64, new 32-bit |
128 | platforms and 32-bit platforms which move into arch/powerpc will be | |
129 | required to use these rules as well. | |
130 | ||
131 | The main requirement that will be defined in more detail below is | |
132 | the presence of a device-tree whose format is defined after Open | |
133 | Firmware specification. However, in order to make life easier | |
134 | to embedded board vendors, the kernel doesn't require the device-tree | |
135 | to represent every device in the system and only requires some nodes | |
136 | and properties to be present. This will be described in detail in | |
137 | section III, but, for example, the kernel does not require you to | |
138 | create a node for every PCI device in the system. It is a requirement | |
139 | to have a node for PCI host bridges in order to provide interrupt | |
140 | routing informations and memory/IO ranges, among others. It is also | |
cf4e5c6e | 141 | recommended to define nodes for on chip devices and other buses that |
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142 | don't specifically fit in an existing OF specification. This creates a |
143 | great flexibility in the way the kernel can then probe those and match | |
144 | drivers to device, without having to hard code all sorts of tables. It | |
145 | also makes it more flexible for board vendors to do minor hardware | |
146 | upgrades without significantly impacting the kernel code or cluttering | |
147 | it with special cases. | |
148 | ||
149 | ||
150 | 1) Entry point for arch/powerpc | |
151 | ------------------------------- | |
152 | ||
cf4e5c6e | 153 | There is one single entry point to the kernel, at the start |
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154 | of the kernel image. That entry point supports two calling |
155 | conventions: | |
156 | ||
157 | a) Boot from Open Firmware. If your firmware is compatible | |
158 | with Open Firmware (IEEE 1275) or provides an OF compatible | |
159 | client interface API (support for "interpret" callback of | |
160 | forth words isn't required), you can enter the kernel with: | |
161 | ||
162 | r5 : OF callback pointer as defined by IEEE 1275 | |
5dd60166 | 163 | bindings to powerpc. Only the 32-bit client interface |
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164 | is currently supported |
165 | ||
166 | r3, r4 : address & length of an initrd if any or 0 | |
167 | ||
168 | The MMU is either on or off; the kernel will run the | |
169 | trampoline located in arch/powerpc/kernel/prom_init.c to | |
170 | extract the device-tree and other information from open | |
171 | firmware and build a flattened device-tree as described | |
172 | in b). prom_init() will then re-enter the kernel using | |
173 | the second method. This trampoline code runs in the | |
174 | context of the firmware, which is supposed to handle all | |
175 | exceptions during that time. | |
176 | ||
177 | b) Direct entry with a flattened device-tree block. This entry | |
178 | point is called by a) after the OF trampoline and can also be | |
179 | called directly by a bootloader that does not support the Open | |
180 | Firmware client interface. It is also used by "kexec" to | |
181 | implement "hot" booting of a new kernel from a previous | |
182 | running one. This method is what I will describe in more | |
183 | details in this document, as method a) is simply standard Open | |
184 | Firmware, and thus should be implemented according to the | |
185 | various standard documents defining it and its binding to the | |
186 | PowerPC platform. The entry point definition then becomes: | |
187 | ||
188 | r3 : physical pointer to the device-tree block | |
189 | (defined in chapter II) in RAM | |
190 | ||
191 | r4 : physical pointer to the kernel itself. This is | |
192 | used by the assembly code to properly disable the MMU | |
193 | in case you are entering the kernel with MMU enabled | |
194 | and a non-1:1 mapping. | |
195 | ||
2fe0ae78 | 196 | r5 : NULL (as to differentiate with method a) |
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197 | |
198 | Note about SMP entry: Either your firmware puts your other | |
199 | CPUs in some sleep loop or spin loop in ROM where you can get | |
200 | them out via a soft reset or some other means, in which case | |
201 | you don't need to care, or you'll have to enter the kernel | |
202 | with all CPUs. The way to do that with method b) will be | |
203 | described in a later revision of this document. | |
204 | ||
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205 | Board supports (platforms) are not exclusive config options. An |
206 | arbitrary set of board supports can be built in a single kernel | |
207 | image. The kernel will "know" what set of functions to use for a | |
208 | given platform based on the content of the device-tree. Thus, you | |
209 | should: | |
210 | ||
211 | a) add your platform support as a _boolean_ option in | |
212 | arch/powerpc/Kconfig, following the example of PPC_PSERIES, | |
213 | PPC_PMAC and PPC_MAPLE. The later is probably a good | |
214 | example of a board support to start from. | |
215 | ||
216 | b) create your main platform file as | |
217 | "arch/powerpc/platforms/myplatform/myboard_setup.c" and add it | |
218 | to the Makefile under the condition of your CONFIG_ | |
219 | option. This file will define a structure of type "ppc_md" | |
220 | containing the various callbacks that the generic code will | |
221 | use to get to your platform specific code | |
222 | ||
cf4e5c6e | 223 | A kernel image may support multiple platforms, but only if the |
5dd60166 | 224 | platforms feature the same core architecture. A single kernel build |
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225 | cannot support both configurations with Book E and configurations |
226 | with classic Powerpc architectures. | |
227 | ||
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228 | |
229 | II - The DT block format | |
230 | ======================== | |
231 | ||
232 | ||
233 | This chapter defines the actual format of the flattened device-tree | |
234 | passed to the kernel. The actual content of it and kernel requirements | |
235 | are described later. You can find example of code manipulating that | |
236 | format in various places, including arch/powerpc/kernel/prom_init.c | |
237 | which will generate a flattened device-tree from the Open Firmware | |
238 | representation, or the fs2dt utility which is part of the kexec tools | |
239 | which will generate one from a filesystem representation. It is | |
240 | expected that a bootloader like uboot provides a bit more support, | |
241 | that will be discussed later as well. | |
242 | ||
243 | Note: The block has to be in main memory. It has to be accessible in | |
244 | both real mode and virtual mode with no mapping other than main | |
245 | memory. If you are writing a simple flash bootloader, it should copy | |
246 | the block to RAM before passing it to the kernel. | |
247 | ||
248 | ||
249 | 1) Header | |
250 | --------- | |
251 | ||
cf4e5c6e GL |
252 | The kernel is passed the physical address pointing to an area of memory |
253 | that is roughly described in include/linux/of_fdt.h by the structure | |
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254 | boot_param_header: |
255 | ||
256 | struct boot_param_header { | |
257 | u32 magic; /* magic word OF_DT_HEADER */ | |
258 | u32 totalsize; /* total size of DT block */ | |
259 | u32 off_dt_struct; /* offset to structure */ | |
260 | u32 off_dt_strings; /* offset to strings */ | |
261 | u32 off_mem_rsvmap; /* offset to memory reserve map | |
5dd60166 | 262 | */ |
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263 | u32 version; /* format version */ |
264 | u32 last_comp_version; /* last compatible version */ | |
265 | ||
266 | /* version 2 fields below */ | |
267 | u32 boot_cpuid_phys; /* Which physical CPU id we're | |
268 | booting on */ | |
269 | /* version 3 fields below */ | |
270 | u32 size_dt_strings; /* size of the strings block */ | |
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271 | |
272 | /* version 17 fields below */ | |
273 | u32 size_dt_struct; /* size of the DT structure block */ | |
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274 | }; |
275 | ||
276 | Along with the constants: | |
277 | ||
278 | /* Definitions used by the flattened device tree */ | |
279 | #define OF_DT_HEADER 0xd00dfeed /* 4: version, | |
280 | 4: total size */ | |
281 | #define OF_DT_BEGIN_NODE 0x1 /* Start node: full name | |
5dd60166 | 282 | */ |
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283 | #define OF_DT_END_NODE 0x2 /* End node */ |
284 | #define OF_DT_PROP 0x3 /* Property: name off, | |
285 | size, content */ | |
286 | #define OF_DT_END 0x9 | |
287 | ||
288 | All values in this header are in big endian format, the various | |
289 | fields in this header are defined more precisely below. All | |
290 | "offset" values are in bytes from the start of the header; that is | |
cf4e5c6e | 291 | from the physical base address of the device tree block. |
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292 | |
293 | - magic | |
294 | ||
295 | This is a magic value that "marks" the beginning of the | |
296 | device-tree block header. It contains the value 0xd00dfeed and is | |
297 | defined by the constant OF_DT_HEADER | |
298 | ||
299 | - totalsize | |
300 | ||
301 | This is the total size of the DT block including the header. The | |
302 | "DT" block should enclose all data structures defined in this | |
303 | chapter (who are pointed to by offsets in this header). That is, | |
304 | the device-tree structure, strings, and the memory reserve map. | |
305 | ||
306 | - off_dt_struct | |
307 | ||
308 | This is an offset from the beginning of the header to the start | |
309 | of the "structure" part the device tree. (see 2) device tree) | |
310 | ||
311 | - off_dt_strings | |
312 | ||
313 | This is an offset from the beginning of the header to the start | |
314 | of the "strings" part of the device-tree | |
315 | ||
316 | - off_mem_rsvmap | |
317 | ||
318 | This is an offset from the beginning of the header to the start | |
5dd60166 | 319 | of the reserved memory map. This map is a list of pairs of 64- |
c125a183 | 320 | bit integers. Each pair is a physical address and a size. The |
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321 | list is terminated by an entry of size 0. This map provides the |
322 | kernel with a list of physical memory areas that are "reserved" | |
323 | and thus not to be used for memory allocations, especially during | |
324 | early initialization. The kernel needs to allocate memory during | |
325 | boot for things like un-flattening the device-tree, allocating an | |
326 | MMU hash table, etc... Those allocations must be done in such a | |
327 | way to avoid overriding critical things like, on Open Firmware | |
328 | capable machines, the RTAS instance, or on some pSeries, the TCE | |
329 | tables used for the iommu. Typically, the reserve map should | |
330 | contain _at least_ this DT block itself (header,total_size). If | |
331 | you are passing an initrd to the kernel, you should reserve it as | |
332 | well. You do not need to reserve the kernel image itself. The map | |
5dd60166 | 333 | should be 64-bit aligned. |
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334 | |
335 | - version | |
336 | ||
337 | This is the version of this structure. Version 1 stops | |
338 | here. Version 2 adds an additional field boot_cpuid_phys. | |
339 | Version 3 adds the size of the strings block, allowing the kernel | |
340 | to reallocate it easily at boot and free up the unused flattened | |
341 | structure after expansion. Version 16 introduces a new more | |
342 | "compact" format for the tree itself that is however not backward | |
0e0293c8 DG |
343 | compatible. Version 17 adds an additional field, size_dt_struct, |
344 | allowing it to be reallocated or moved more easily (this is | |
345 | particularly useful for bootloaders which need to make | |
346 | adjustments to a device tree based on probed information). You | |
347 | should always generate a structure of the highest version defined | |
348 | at the time of your implementation. Currently that is version 17, | |
349 | unless you explicitly aim at being backward compatible. | |
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350 | |
351 | - last_comp_version | |
352 | ||
353 | Last compatible version. This indicates down to what version of | |
354 | the DT block you are backward compatible. For example, version 2 | |
355 | is backward compatible with version 1 (that is, a kernel build | |
356 | for version 1 will be able to boot with a version 2 format). You | |
357 | should put a 1 in this field if you generate a device tree of | |
0e0293c8 | 358 | version 1 to 3, or 16 if you generate a tree of version 16 or 17 |
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359 | using the new unit name format. |
360 | ||
361 | - boot_cpuid_phys | |
362 | ||
363 | This field only exist on version 2 headers. It indicate which | |
364 | physical CPU ID is calling the kernel entry point. This is used, | |
365 | among others, by kexec. If you are on an SMP system, this value | |
366 | should match the content of the "reg" property of the CPU node in | |
367 | the device-tree corresponding to the CPU calling the kernel entry | |
368 | point (see further chapters for more informations on the required | |
369 | device-tree contents) | |
370 | ||
0e0293c8 DG |
371 | - size_dt_strings |
372 | ||
373 | This field only exists on version 3 and later headers. It | |
374 | gives the size of the "strings" section of the device tree (which | |
375 | starts at the offset given by off_dt_strings). | |
376 | ||
377 | - size_dt_struct | |
378 | ||
379 | This field only exists on version 17 and later headers. It gives | |
380 | the size of the "structure" section of the device tree (which | |
381 | starts at the offset given by off_dt_struct). | |
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382 | |
383 | So the typical layout of a DT block (though the various parts don't | |
384 | need to be in that order) looks like this (addresses go from top to | |
385 | bottom): | |
386 | ||
387 | ||
388 | ------------------------------ | |
cf4e5c6e | 389 | base -> | struct boot_param_header | |
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390 | ------------------------------ |
391 | | (alignment gap) (*) | | |
392 | ------------------------------ | |
393 | | memory reserve map | | |
394 | ------------------------------ | |
395 | | (alignment gap) | | |
396 | ------------------------------ | |
397 | | | | |
398 | | device-tree structure | | |
399 | | | | |
400 | ------------------------------ | |
401 | | (alignment gap) | | |
402 | ------------------------------ | |
403 | | | | |
404 | | device-tree strings | | |
405 | | | | |
406 | -----> ------------------------------ | |
407 | | | |
408 | | | |
cf4e5c6e | 409 | --- (base + totalsize) |
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410 | |
411 | (*) The alignment gaps are not necessarily present; their presence | |
412 | and size are dependent on the various alignment requirements of | |
413 | the individual data blocks. | |
414 | ||
415 | ||
416 | 2) Device tree generalities | |
417 | --------------------------- | |
418 | ||
419 | This device-tree itself is separated in two different blocks, a | |
420 | structure block and a strings block. Both need to be aligned to a 4 | |
421 | byte boundary. | |
422 | ||
423 | First, let's quickly describe the device-tree concept before detailing | |
424 | the storage format. This chapter does _not_ describe the detail of the | |
425 | required types of nodes & properties for the kernel, this is done | |
426 | later in chapter III. | |
427 | ||
428 | The device-tree layout is strongly inherited from the definition of | |
429 | the Open Firmware IEEE 1275 device-tree. It's basically a tree of | |
430 | nodes, each node having two or more named properties. A property can | |
431 | have a value or not. | |
432 | ||
433 | It is a tree, so each node has one and only one parent except for the | |
434 | root node who has no parent. | |
435 | ||
436 | A node has 2 names. The actual node name is generally contained in a | |
437 | property of type "name" in the node property list whose value is a | |
438 | zero terminated string and is mandatory for version 1 to 3 of the | |
0e0293c8 | 439 | format definition (as it is in Open Firmware). Version 16 makes it |
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440 | optional as it can generate it from the unit name defined below. |
441 | ||
2fe0ae78 | 442 | There is also a "unit name" that is used to differentiate nodes with |
c125a183 | 443 | the same name at the same level, it is usually made of the node |
2fe0ae78 | 444 | names, the "@" sign, and a "unit address", which definition is |
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445 | specific to the bus type the node sits on. |
446 | ||
447 | The unit name doesn't exist as a property per-se but is included in | |
448 | the device-tree structure. It is typically used to represent "path" in | |
449 | the device-tree. More details about the actual format of these will be | |
450 | below. | |
451 | ||
cf4e5c6e | 452 | The kernel generic code does not make any formal use of the |
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453 | unit address (though some board support code may do) so the only real |
454 | requirement here for the unit address is to ensure uniqueness of | |
455 | the node unit name at a given level of the tree. Nodes with no notion | |
456 | of address and no possible sibling of the same name (like /memory or | |
457 | /cpus) may omit the unit address in the context of this specification, | |
458 | or use the "@0" default unit address. The unit name is used to define | |
459 | a node "full path", which is the concatenation of all parent node | |
460 | unit names separated with "/". | |
461 | ||
462 | The root node doesn't have a defined name, and isn't required to have | |
463 | a name property either if you are using version 3 or earlier of the | |
464 | format. It also has no unit address (no @ symbol followed by a unit | |
465 | address). The root node unit name is thus an empty string. The full | |
466 | path to the root node is "/". | |
467 | ||
468 | Every node which actually represents an actual device (that is, a node | |
469 | which isn't only a virtual "container" for more nodes, like "/cpus" | |
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470 | is) is also required to have a "compatible" property indicating the |
471 | specific hardware and an optional list of devices it is fully | |
472 | backwards compatible with. | |
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473 | |
474 | Finally, every node that can be referenced from a property in another | |
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475 | node is required to have either a "phandle" or a "linux,phandle" |
476 | property. Real Open Firmware implementations provide a unique | |
477 | "phandle" value for every node that the "prom_init()" trampoline code | |
478 | turns into "linux,phandle" properties. However, this is made optional | |
479 | if the flattened device tree is used directly. An example of a node | |
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480 | referencing another node via "phandle" is when laying out the |
481 | interrupt tree which will be described in a further version of this | |
482 | document. | |
483 | ||
cf4e5c6e | 484 | The "phandle" property is a 32-bit value that uniquely |
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485 | identifies a node. You are free to use whatever values or system of |
486 | values, internal pointers, or whatever to generate these, the only | |
487 | requirement is that every node for which you provide that property has | |
488 | a unique value for it. | |
489 | ||
490 | Here is an example of a simple device-tree. In this example, an "o" | |
491 | designates a node followed by the node unit name. Properties are | |
492 | presented with their name followed by their content. "content" | |
493 | represents an ASCII string (zero terminated) value, while <content> | |
5dd60166 | 494 | represents a 32-bit hexadecimal value. The various nodes in this |
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495 | example will be discussed in a later chapter. At this point, it is |
496 | only meant to give you a idea of what a device-tree looks like. I have | |
497 | purposefully kept the "name" and "linux,phandle" properties which | |
498 | aren't necessary in order to give you a better idea of what the tree | |
499 | looks like in practice. | |
500 | ||
501 | / o device-tree | |
502 | |- name = "device-tree" | |
503 | |- model = "MyBoardName" | |
504 | |- compatible = "MyBoardFamilyName" | |
505 | |- #address-cells = <2> | |
506 | |- #size-cells = <2> | |
507 | |- linux,phandle = <0> | |
508 | | | |
509 | o cpus | |
510 | | | - name = "cpus" | |
511 | | | - linux,phandle = <1> | |
512 | | | - #address-cells = <1> | |
513 | | | - #size-cells = <0> | |
514 | | | | |
515 | | o PowerPC,970@0 | |
516 | | |- name = "PowerPC,970" | |
517 | | |- device_type = "cpu" | |
518 | | |- reg = <0> | |
519 | | |- clock-frequency = <5f5e1000> | |
32aed2a5 | 520 | | |- 64-bit |
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521 | | |- linux,phandle = <2> |
522 | | | |
523 | o memory@0 | |
524 | | |- name = "memory" | |
525 | | |- device_type = "memory" | |
526 | | |- reg = <00000000 00000000 00000000 20000000> | |
527 | | |- linux,phandle = <3> | |
528 | | | |
529 | o chosen | |
530 | |- name = "chosen" | |
531 | |- bootargs = "root=/dev/sda2" | |
c125a183 DG |
532 | |- linux,phandle = <4> |
533 | ||
534 | This tree is almost a minimal tree. It pretty much contains the | |
535 | minimal set of required nodes and properties to boot a linux kernel; | |
536 | that is, some basic model informations at the root, the CPUs, and the | |
537 | physical memory layout. It also includes misc information passed | |
538 | through /chosen, like in this example, the platform type (mandatory) | |
539 | and the kernel command line arguments (optional). | |
540 | ||
32aed2a5 | 541 | The /cpus/PowerPC,970@0/64-bit property is an example of a |
c125a183 DG |
542 | property without a value. All other properties have a value. The |
543 | significance of the #address-cells and #size-cells properties will be | |
544 | explained in chapter IV which defines precisely the required nodes and | |
545 | properties and their content. | |
546 | ||
547 | ||
548 | 3) Device tree "structure" block | |
549 | ||
550 | The structure of the device tree is a linearized tree structure. The | |
551 | "OF_DT_BEGIN_NODE" token starts a new node, and the "OF_DT_END_NODE" | |
552 | ends that node definition. Child nodes are simply defined before | |
553 | "OF_DT_END_NODE" (that is nodes within the node). A 'token' is a 32 | |
554 | bit value. The tree has to be "finished" with a OF_DT_END token | |
555 | ||
556 | Here's the basic structure of a single node: | |
557 | ||
558 | * token OF_DT_BEGIN_NODE (that is 0x00000001) | |
559 | * for version 1 to 3, this is the node full path as a zero | |
560 | terminated string, starting with "/". For version 16 and later, | |
561 | this is the node unit name only (or an empty string for the | |
562 | root node) | |
563 | * [align gap to next 4 bytes boundary] | |
564 | * for each property: | |
565 | * token OF_DT_PROP (that is 0x00000003) | |
5dd60166 DP |
566 | * 32-bit value of property value size in bytes (or 0 if no |
567 | value) | |
568 | * 32-bit value of offset in string block of property name | |
c125a183 DG |
569 | * property value data if any |
570 | * [align gap to next 4 bytes boundary] | |
571 | * [child nodes if any] | |
572 | * token OF_DT_END_NODE (that is 0x00000002) | |
573 | ||
5dd60166 | 574 | So the node content can be summarized as a start token, a full path, |
53cb4726 | 575 | a list of properties, a list of child nodes, and an end token. Every |
c125a183 DG |
576 | child node is a full node structure itself as defined above. |
577 | ||
eff2ebd2 DG |
578 | NOTE: The above definition requires that all property definitions for |
579 | a particular node MUST precede any subnode definitions for that node. | |
580 | Although the structure would not be ambiguous if properties and | |
581 | subnodes were intermingled, the kernel parser requires that the | |
582 | properties come first (up until at least 2.6.22). Any tools | |
583 | manipulating a flattened tree must take care to preserve this | |
584 | constraint. | |
585 | ||
53cb4726 | 586 | 4) Device tree "strings" block |
c125a183 DG |
587 | |
588 | In order to save space, property names, which are generally redundant, | |
589 | are stored separately in the "strings" block. This block is simply the | |
590 | whole bunch of zero terminated strings for all property names | |
591 | concatenated together. The device-tree property definitions in the | |
592 | structure block will contain offset values from the beginning of the | |
593 | strings block. | |
594 | ||
595 | ||
596 | III - Required content of the device tree | |
597 | ========================================= | |
598 | ||
599 | WARNING: All "linux,*" properties defined in this document apply only | |
600 | to a flattened device-tree. If your platform uses a real | |
601 | implementation of Open Firmware or an implementation compatible with | |
602 | the Open Firmware client interface, those properties will be created | |
603 | by the trampoline code in the kernel's prom_init() file. For example, | |
604 | that's where you'll have to add code to detect your board model and | |
a2ffd275 | 605 | set the platform number. However, when using the flattened device-tree |
c125a183 DG |
606 | entry point, there is no prom_init() pass, and thus you have to |
607 | provide those properties yourself. | |
608 | ||
609 | ||
610 | 1) Note about cells and address representation | |
611 | ---------------------------------------------- | |
612 | ||
613 | The general rule is documented in the various Open Firmware | |
5dd60166 | 614 | documentations. If you choose to describe a bus with the device-tree |
c125a183 DG |
615 | and there exist an OF bus binding, then you should follow the |
616 | specification. However, the kernel does not require every single | |
617 | device or bus to be described by the device tree. | |
618 | ||
619 | In general, the format of an address for a device is defined by the | |
620 | parent bus type, based on the #address-cells and #size-cells | |
5b14e5f9 | 621 | properties. Note that the parent's parent definitions of #address-cells |
d9195881 | 622 | and #size-cells are not inherited so every node with children must specify |
5b14e5f9 MG |
623 | them. The kernel requires the root node to have those properties defining |
624 | addresses format for devices directly mapped on the processor bus. | |
c125a183 DG |
625 | |
626 | Those 2 properties define 'cells' for representing an address and a | |
5dd60166 | 627 | size. A "cell" is a 32-bit number. For example, if both contain 2 |
c125a183 | 628 | like the example tree given above, then an address and a size are both |
5dd60166 | 629 | composed of 2 cells, and each is a 64-bit number (cells are |
c125a183 DG |
630 | concatenated and expected to be in big endian format). Another example |
631 | is the way Apple firmware defines them, with 2 cells for an address | |
632 | and one cell for a size. Most 32-bit implementations should define | |
633 | #address-cells and #size-cells to 1, which represents a 32-bit value. | |
634 | Some 32-bit processors allow for physical addresses greater than 32 | |
635 | bits; these processors should define #address-cells as 2. | |
636 | ||
637 | "reg" properties are always a tuple of the type "address size" where | |
638 | the number of cells of address and size is specified by the bus | |
639 | #address-cells and #size-cells. When a bus supports various address | |
640 | spaces and other flags relative to a given address allocation (like | |
641 | prefetchable, etc...) those flags are usually added to the top level | |
642 | bits of the physical address. For example, a PCI physical address is | |
643 | made of 3 cells, the bottom two containing the actual address itself | |
644 | while the top cell contains address space indication, flags, and pci | |
645 | bus & device numbers. | |
646 | ||
cf4e5c6e | 647 | For buses that support dynamic allocation, it's the accepted practice |
c125a183 DG |
648 | to then not provide the address in "reg" (keep it 0) though while |
649 | providing a flag indicating the address is dynamically allocated, and | |
650 | then, to provide a separate "assigned-addresses" property that | |
651 | contains the fully allocated addresses. See the PCI OF bindings for | |
652 | details. | |
653 | ||
654 | In general, a simple bus with no address space bits and no dynamic | |
655 | allocation is preferred if it reflects your hardware, as the existing | |
656 | kernel address parsing functions will work out of the box. If you | |
657 | define a bus type with a more complex address format, including things | |
658 | like address space bits, you'll have to add a bus translator to the | |
659 | prom_parse.c file of the recent kernels for your bus type. | |
660 | ||
e1fd1865 SN |
661 | The "reg" property only defines addresses and sizes (if #size-cells is |
662 | non-0) within a given bus. In order to translate addresses upward | |
5dd60166 | 663 | (that is into parent bus addresses, and possibly into CPU physical |
cf4e5c6e | 664 | addresses), all buses must contain a "ranges" property. If the |
c125a183 | 665 | "ranges" property is missing at a given level, it's assumed that |
e1fd1865 SN |
666 | translation isn't possible, i.e., the registers are not visible on the |
667 | parent bus. The format of the "ranges" property for a bus is a list | |
668 | of: | |
c125a183 DG |
669 | |
670 | bus address, parent bus address, size | |
671 | ||
672 | "bus address" is in the format of the bus this bus node is defining, | |
673 | that is, for a PCI bridge, it would be a PCI address. Thus, (bus | |
674 | address, size) defines a range of addresses for child devices. "parent | |
675 | bus address" is in the format of the parent bus of this bus. For | |
676 | example, for a PCI host controller, that would be a CPU address. For a | |
677 | PCI<->ISA bridge, that would be a PCI address. It defines the base | |
678 | address in the parent bus where the beginning of that range is mapped. | |
679 | ||
cf4e5c6e | 680 | For new 64-bit board support, I recommend either the 2/2 format or |
c125a183 | 681 | Apple's 2/1 format which is slightly more compact since sizes usually |
cf4e5c6e | 682 | fit in a single 32-bit word. New 32-bit board support should use a |
c125a183 DG |
683 | 1/1 format, unless the processor supports physical addresses greater |
684 | than 32-bits, in which case a 2/1 format is recommended. | |
685 | ||
e1fd1865 SN |
686 | Alternatively, the "ranges" property may be empty, indicating that the |
687 | registers are visible on the parent bus using an identity mapping | |
688 | translation. In other words, the parent bus address space is the same | |
689 | as the child bus address space. | |
c125a183 DG |
690 | |
691 | 2) Note about "compatible" properties | |
692 | ------------------------------------- | |
693 | ||
694 | These properties are optional, but recommended in devices and the root | |
695 | node. The format of a "compatible" property is a list of concatenated | |
696 | zero terminated strings. They allow a device to express its | |
697 | compatibility with a family of similar devices, in some cases, | |
698 | allowing a single driver to match against several devices regardless | |
699 | of their actual names. | |
700 | ||
701 | 3) Note about "name" properties | |
702 | ------------------------------- | |
703 | ||
704 | While earlier users of Open Firmware like OldWorld macintoshes tended | |
705 | to use the actual device name for the "name" property, it's nowadays | |
706 | considered a good practice to use a name that is closer to the device | |
cf4e5c6e | 707 | class (often equal to device_type). For example, nowadays, Ethernet |
c125a183 DG |
708 | controllers are named "ethernet", an additional "model" property |
709 | defining precisely the chip type/model, and "compatible" property | |
710 | defining the family in case a single driver can driver more than one | |
711 | of these chips. However, the kernel doesn't generally put any | |
712 | restriction on the "name" property; it is simply considered good | |
713 | practice to follow the standard and its evolutions as closely as | |
714 | possible. | |
715 | ||
716 | Note also that the new format version 16 makes the "name" property | |
717 | optional. If it's absent for a node, then the node's unit name is then | |
718 | used to reconstruct the name. That is, the part of the unit name | |
719 | before the "@" sign is used (or the entire unit name if no "@" sign | |
720 | is present). | |
721 | ||
722 | 4) Note about node and property names and character set | |
723 | ------------------------------------------------------- | |
724 | ||
cf4e5c6e | 725 | While Open Firmware provides more flexible usage of 8859-1, this |
c125a183 DG |
726 | specification enforces more strict rules. Nodes and properties should |
727 | be comprised only of ASCII characters 'a' to 'z', '0' to | |
728 | '9', ',', '.', '_', '+', '#', '?', and '-'. Node names additionally | |
729 | allow uppercase characters 'A' to 'Z' (property names should be | |
730 | lowercase. The fact that vendors like Apple don't respect this rule is | |
731 | irrelevant here). Additionally, node and property names should always | |
732 | begin with a character in the range 'a' to 'z' (or 'A' to 'Z' for node | |
733 | names). | |
734 | ||
735 | The maximum number of characters for both nodes and property names | |
736 | is 31. In the case of node names, this is only the leftmost part of | |
737 | a unit name (the pure "name" property), it doesn't include the unit | |
738 | address which can extend beyond that limit. | |
739 | ||
740 | ||
741 | 5) Required nodes and properties | |
742 | -------------------------------- | |
743 | These are all that are currently required. However, it is strongly | |
744 | recommended that you expose PCI host bridges as documented in the | |
cf4e5c6e | 745 | PCI binding to Open Firmware, and your interrupt tree as documented |
c125a183 DG |
746 | in OF interrupt tree specification. |
747 | ||
748 | a) The root node | |
749 | ||
750 | The root node requires some properties to be present: | |
751 | ||
752 | - model : this is your board name/model | |
753 | - #address-cells : address representation for "root" devices | |
754 | - #size-cells: the size representation for "root" devices | |
c125a183 DG |
755 | - compatible : the board "family" generally finds its way here, |
756 | for example, if you have 2 board models with a similar layout, | |
757 | that typically get driven by the same platform code in the | |
cf4e5c6e GL |
758 | kernel, you would specify the exact board model in the |
759 | compatible property followed by an entry that represents the SoC | |
760 | model. | |
c125a183 DG |
761 | |
762 | The root node is also generally where you add additional properties | |
763 | specific to your board like the serial number if any, that sort of | |
6c28f2c0 | 764 | thing. It is recommended that if you add any "custom" property whose |
c125a183 DG |
765 | name may clash with standard defined ones, you prefix them with your |
766 | vendor name and a comma. | |
767 | ||
768 | b) The /cpus node | |
769 | ||
770 | This node is the parent of all individual CPU nodes. It doesn't | |
771 | have any specific requirements, though it's generally good practice | |
772 | to have at least: | |
773 | ||
774 | #address-cells = <00000001> | |
775 | #size-cells = <00000000> | |
776 | ||
777 | This defines that the "address" for a CPU is a single cell, and has | |
778 | no meaningful size. This is not necessary but the kernel will assume | |
779 | that format when reading the "reg" properties of a CPU node, see | |
780 | below | |
781 | ||
782 | c) The /cpus/* nodes | |
783 | ||
784 | So under /cpus, you are supposed to create a node for every CPU on | |
785 | the machine. There is no specific restriction on the name of the | |
cf4e5c6e | 786 | CPU, though it's common to call it <architecture>,<core>. For |
c125a183 | 787 | example, Apple uses PowerPC,G5 while IBM uses PowerPC,970FX. |
cf4e5c6e GL |
788 | However, the Generic Names convention suggests that it would be |
789 | better to simply use 'cpu' for each cpu node and use the compatible | |
790 | property to identify the specific cpu core. | |
c125a183 DG |
791 | |
792 | Required properties: | |
793 | ||
794 | - device_type : has to be "cpu" | |
5dd60166 | 795 | - reg : This is the physical CPU number, it's a single 32-bit cell |
c125a183 DG |
796 | and is also used as-is as the unit number for constructing the |
797 | unit name in the full path. For example, with 2 CPUs, you would | |
798 | have the full path: | |
799 | /cpus/PowerPC,970FX@0 | |
800 | /cpus/PowerPC,970FX@1 | |
801 | (unit addresses do not require leading zeroes) | |
20474abd BH |
802 | - d-cache-block-size : one cell, L1 data cache block size in bytes (*) |
803 | - i-cache-block-size : one cell, L1 instruction cache block size in | |
c125a183 DG |
804 | bytes |
805 | - d-cache-size : one cell, size of L1 data cache in bytes | |
806 | - i-cache-size : one cell, size of L1 instruction cache in bytes | |
c125a183 | 807 | |
20474abd BH |
808 | (*) The cache "block" size is the size on which the cache management |
809 | instructions operate. Historically, this document used the cache | |
810 | "line" size here which is incorrect. The kernel will prefer the cache | |
811 | block size and will fallback to cache line size for backward | |
812 | compatibility. | |
813 | ||
c125a183 DG |
814 | Recommended properties: |
815 | ||
816 | - timebase-frequency : a cell indicating the frequency of the | |
817 | timebase in Hz. This is not directly used by the generic code, | |
818 | but you are welcome to copy/paste the pSeries code for setting | |
819 | the kernel timebase/decrementer calibration based on this | |
820 | value. | |
821 | - clock-frequency : a cell indicating the CPU core clock frequency | |
5dd60166 | 822 | in Hz. A new property will be defined for 64-bit values, but if |
c125a183 DG |
823 | your frequency is < 4Ghz, one cell is enough. Here as well as |
824 | for the above, the common code doesn't use that property, but | |
825 | you are welcome to re-use the pSeries or Maple one. A future | |
826 | kernel version might provide a common function for this. | |
20474abd BH |
827 | - d-cache-line-size : one cell, L1 data cache line size in bytes |
828 | if different from the block size | |
829 | - i-cache-line-size : one cell, L1 instruction cache line size in | |
830 | bytes if different from the block size | |
c125a183 DG |
831 | |
832 | You are welcome to add any property you find relevant to your board, | |
833 | like some information about the mechanism used to soft-reset the | |
834 | CPUs. For example, Apple puts the GPIO number for CPU soft reset | |
835 | lines in there as a "soft-reset" property since they start secondary | |
836 | CPUs by soft-resetting them. | |
837 | ||
838 | ||
839 | d) the /memory node(s) | |
840 | ||
841 | To define the physical memory layout of your board, you should | |
842 | create one or more memory node(s). You can either create a single | |
843 | node with all memory ranges in its reg property, or you can create | |
844 | several nodes, as you wish. The unit address (@ part) used for the | |
845 | full path is the address of the first range of memory defined by a | |
846 | given node. If you use a single memory node, this will typically be | |
847 | @0. | |
848 | ||
849 | Required properties: | |
850 | ||
851 | - device_type : has to be "memory" | |
852 | - reg : This property contains all the physical memory ranges of | |
853 | your board. It's a list of addresses/sizes concatenated | |
854 | together, with the number of cells of each defined by the | |
855 | #address-cells and #size-cells of the root node. For example, | |
6c28f2c0 | 856 | with both of these properties being 2 like in the example given |
c125a183 DG |
857 | earlier, a 970 based machine with 6Gb of RAM could typically |
858 | have a "reg" property here that looks like: | |
859 | ||
860 | 00000000 00000000 00000000 80000000 | |
861 | 00000001 00000000 00000001 00000000 | |
862 | ||
863 | That is a range starting at 0 of 0x80000000 bytes and a range | |
864 | starting at 0x100000000 and of 0x100000000 bytes. You can see | |
865 | that there is no memory covering the IO hole between 2Gb and | |
866 | 4Gb. Some vendors prefer splitting those ranges into smaller | |
867 | segments, but the kernel doesn't care. | |
868 | ||
869 | e) The /chosen node | |
870 | ||
cf4e5c6e | 871 | This node is a bit "special". Normally, that's where Open Firmware |
c125a183 | 872 | puts some variable environment information, like the arguments, or |
d1bff9ed | 873 | the default input/output devices. |
c125a183 DG |
874 | |
875 | This specification makes a few of these mandatory, but also defines | |
876 | some linux-specific properties that would be normally constructed by | |
877 | the prom_init() trampoline when booting with an OF client interface, | |
878 | but that you have to provide yourself when using the flattened format. | |
879 | ||
c125a183 DG |
880 | Recommended properties: |
881 | ||
882 | - bootargs : This zero-terminated string is passed as the kernel | |
883 | command line | |
884 | - linux,stdout-path : This is the full path to your standard | |
885 | console device if any. Typically, if you have serial devices on | |
886 | your board, you may want to put the full path to the one set as | |
887 | the default console in the firmware here, for the kernel to pick | |
cf4e5c6e | 888 | it up as its own default console. |
c125a183 DG |
889 | |
890 | Note that u-boot creates and fills in the chosen node for platforms | |
891 | that use it. | |
892 | ||
d1bff9ed SY |
893 | (Note: a practice that is now obsolete was to include a property |
894 | under /chosen called interrupt-controller which had a phandle value | |
895 | that pointed to the main interrupt controller) | |
896 | ||
c125a183 DG |
897 | f) the /soc<SOCname> node |
898 | ||
cf4e5c6e GL |
899 | This node is used to represent a system-on-a-chip (SoC) and must be |
900 | present if the processor is a SoC. The top-level soc node contains | |
901 | information that is global to all devices on the SoC. The node name | |
902 | should contain a unit address for the SoC, which is the base address | |
903 | of the memory-mapped register set for the SoC. The name of an SoC | |
c125a183 DG |
904 | node should start with "soc", and the remainder of the name should |
905 | represent the part number for the soc. For example, the MPC8540's | |
906 | soc node would be called "soc8540". | |
907 | ||
908 | Required properties: | |
909 | ||
c125a183 | 910 | - ranges : Should be defined as specified in 1) to describe the |
cf4e5c6e GL |
911 | translation of SoC addresses for memory mapped SoC registers. |
912 | - bus-frequency: Contains the bus frequency for the SoC node. | |
7d4b95ae | 913 | Typically, the value of this field is filled in by the boot |
efcc2da3 | 914 | loader. |
cf4e5c6e | 915 | - compatible : Exact model of the SoC |
7d4b95ae | 916 | |
c125a183 DG |
917 | |
918 | Recommended properties: | |
919 | ||
920 | - reg : This property defines the address and size of the | |
921 | memory-mapped registers that are used for the SOC node itself. | |
922 | It does not include the child device registers - these will be | |
923 | defined inside each child node. The address specified in the | |
924 | "reg" property should match the unit address of the SOC node. | |
925 | - #address-cells : Address representation for "soc" devices. The | |
926 | format of this field may vary depending on whether or not the | |
927 | device registers are memory mapped. For memory mapped | |
928 | registers, this field represents the number of cells needed to | |
929 | represent the address of the registers. For SOCs that do not | |
930 | use MMIO, a special address format should be defined that | |
931 | contains enough cells to represent the required information. | |
932 | See 1) above for more details on defining #address-cells. | |
933 | - #size-cells : Size representation for "soc" devices | |
934 | - #interrupt-cells : Defines the width of cells used to represent | |
935 | interrupts. Typically this value is <2>, which includes a | |
936 | 32-bit number that represents the interrupt number, and a | |
937 | 32-bit number that represents the interrupt sense and level. | |
938 | This field is only needed if the SOC contains an interrupt | |
939 | controller. | |
940 | ||
941 | The SOC node may contain child nodes for each SOC device that the | |
942 | platform uses. Nodes should not be created for devices which exist | |
943 | on the SOC but are not used by a particular platform. See chapter VI | |
5dd60166 | 944 | for more information on how to specify devices that are part of a SOC. |
c125a183 DG |
945 | |
946 | Example SOC node for the MPC8540: | |
947 | ||
948 | soc8540@e0000000 { | |
949 | #address-cells = <1>; | |
950 | #size-cells = <1>; | |
951 | #interrupt-cells = <2>; | |
952 | device_type = "soc"; | |
953 | ranges = <00000000 e0000000 00100000> | |
954 | reg = <e0000000 00003000>; | |
7d4b95ae | 955 | bus-frequency = <0>; |
c125a183 DG |
956 | } |
957 | ||
958 | ||
959 | ||
960 | IV - "dtc", the device tree compiler | |
961 | ==================================== | |
962 | ||
963 | ||
964 | dtc source code can be found at | |
0ea6e611 | 965 | <http://git.jdl.com/gitweb/?p=dtc.git> |
c125a183 DG |
966 | |
967 | WARNING: This version is still in early development stage; the | |
968 | resulting device-tree "blobs" have not yet been validated with the | |
475fc7c0 | 969 | kernel. The current generated block lacks a useful reserve map (it will |
c125a183 DG |
970 | be fixed to generate an empty one, it's up to the bootloader to fill |
971 | it up) among others. The error handling needs work, bugs are lurking, | |
972 | etc... | |
973 | ||
974 | dtc basically takes a device-tree in a given format and outputs a | |
975 | device-tree in another format. The currently supported formats are: | |
976 | ||
977 | Input formats: | |
978 | ------------- | |
979 | ||
980 | - "dtb": "blob" format, that is a flattened device-tree block | |
981 | with | |
982 | header all in a binary blob. | |
983 | - "dts": "source" format. This is a text file containing a | |
984 | "source" for a device-tree. The format is defined later in this | |
985 | chapter. | |
986 | - "fs" format. This is a representation equivalent to the | |
987 | output of /proc/device-tree, that is nodes are directories and | |
988 | properties are files | |
989 | ||
990 | Output formats: | |
991 | --------------- | |
992 | ||
993 | - "dtb": "blob" format | |
994 | - "dts": "source" format | |
995 | - "asm": assembly language file. This is a file that can be | |
996 | sourced by gas to generate a device-tree "blob". That file can | |
997 | then simply be added to your Makefile. Additionally, the | |
6c28f2c0 | 998 | assembly file exports some symbols that can be used. |
c125a183 DG |
999 | |
1000 | ||
1001 | The syntax of the dtc tool is | |
1002 | ||
1003 | dtc [-I <input-format>] [-O <output-format>] | |
1004 | [-o output-filename] [-V output_version] input_filename | |
1005 | ||
1006 | ||
5dd60166 | 1007 | The "output_version" defines what version of the "blob" format will be |
c125a183 DG |
1008 | generated. Supported versions are 1,2,3 and 16. The default is |
1009 | currently version 3 but that may change in the future to version 16. | |
1010 | ||
1011 | Additionally, dtc performs various sanity checks on the tree, like the | |
6c28f2c0 | 1012 | uniqueness of linux, phandle properties, validity of strings, etc... |
c125a183 DG |
1013 | |
1014 | The format of the .dts "source" file is "C" like, supports C and C++ | |
6c28f2c0 | 1015 | style comments. |
c125a183 DG |
1016 | |
1017 | / { | |
1018 | } | |
1019 | ||
1020 | The above is the "device-tree" definition. It's the only statement | |
1021 | supported currently at the toplevel. | |
1022 | ||
1023 | / { | |
1024 | property1 = "string_value"; /* define a property containing a 0 | |
1025 | * terminated string | |
1026 | */ | |
1027 | ||
1028 | property2 = <1234abcd>; /* define a property containing a | |
5dd60166 | 1029 | * numerical 32-bit value (hexadecimal) |
c125a183 DG |
1030 | */ |
1031 | ||
1032 | property3 = <12345678 12345678 deadbeef>; | |
1033 | /* define a property containing 3 | |
5dd60166 | 1034 | * numerical 32-bit values (cells) in |
c125a183 DG |
1035 | * hexadecimal |
1036 | */ | |
1037 | property4 = [0a 0b 0c 0d de ea ad be ef]; | |
1038 | /* define a property whose content is | |
1039 | * an arbitrary array of bytes | |
1040 | */ | |
1041 | ||
b595076a | 1042 | childnode@address { /* define a child node named "childnode" |
c125a183 DG |
1043 | * whose unit name is "childnode at |
1044 | * address" | |
1045 | */ | |
1046 | ||
1047 | childprop = "hello\n"; /* define a property "childprop" of | |
1048 | * childnode (in this case, a string) | |
1049 | */ | |
1050 | }; | |
1051 | }; | |
1052 | ||
1053 | Nodes can contain other nodes etc... thus defining the hierarchical | |
1054 | structure of the tree. | |
1055 | ||
1056 | Strings support common escape sequences from C: "\n", "\t", "\r", | |
1057 | "\(octal value)", "\x(hex value)". | |
1058 | ||
1059 | It is also suggested that you pipe your source file through cpp (gcc | |
1060 | preprocessor) so you can use #include's, #define for constants, etc... | |
1061 | ||
1062 | Finally, various options are planned but not yet implemented, like | |
1063 | automatic generation of phandles, labels (exported to the asm file so | |
1064 | you can point to a property content and change it easily from whatever | |
1065 | you link the device-tree with), label or path instead of numeric value | |
1066 | in some cells to "point" to a node (replaced by a phandle at compile | |
1067 | time), export of reserve map address to the asm file, ability to | |
1068 | specify reserve map content at compile time, etc... | |
1069 | ||
1070 | We may provide a .h include file with common definitions of that | |
1071 | proves useful for some properties (like building PCI properties or | |
1072 | interrupt maps) though it may be better to add a notion of struct | |
1073 | definitions to the compiler... | |
1074 | ||
1075 | ||
1076 | V - Recommendations for a bootloader | |
1077 | ==================================== | |
1078 | ||
1079 | ||
1080 | Here are some various ideas/recommendations that have been proposed | |
1081 | while all this has been defined and implemented. | |
1082 | ||
1083 | - The bootloader may want to be able to use the device-tree itself | |
1084 | and may want to manipulate it (to add/edit some properties, | |
1085 | like physical memory size or kernel arguments). At this point, 2 | |
1086 | choices can be made. Either the bootloader works directly on the | |
1087 | flattened format, or the bootloader has its own internal tree | |
1088 | representation with pointers (similar to the kernel one) and | |
1089 | re-flattens the tree when booting the kernel. The former is a bit | |
1090 | more difficult to edit/modify, the later requires probably a bit | |
1091 | more code to handle the tree structure. Note that the structure | |
1092 | format has been designed so it's relatively easy to "insert" | |
1093 | properties or nodes or delete them by just memmoving things | |
1094 | around. It contains no internal offsets or pointers for this | |
1095 | purpose. | |
1096 | ||
d6bc8ac9 | 1097 | - An example of code for iterating nodes & retrieving properties |
c125a183 | 1098 | directly from the flattened tree format can be found in the kernel |
cf4e5c6e | 1099 | file drivers/of/fdt.c. Look at the of_scan_flat_dt() function, |
d6bc8ac9 | 1100 | its usage in early_init_devtree(), and the corresponding various |
c125a183 DG |
1101 | early_init_dt_scan_*() callbacks. That code can be re-used in a |
1102 | GPL bootloader, and as the author of that code, I would be happy | |
5dd60166 | 1103 | to discuss possible free licensing to any vendor who wishes to |
c125a183 | 1104 | integrate all or part of this code into a non-GPL bootloader. |
cf4e5c6e | 1105 | (reference needed; who is 'I' here? ---gcl Jan 31, 2011) |
c125a183 DG |
1106 | |
1107 | ||
1108 | ||
1109 | VI - System-on-a-chip devices and nodes | |
1110 | ======================================= | |
1111 | ||
1112 | Many companies are now starting to develop system-on-a-chip | |
5dd60166 | 1113 | processors, where the processor core (CPU) and many peripheral devices |
c125a183 DG |
1114 | exist on a single piece of silicon. For these SOCs, an SOC node |
1115 | should be used that defines child nodes for the devices that make | |
1116 | up the SOC. While platforms are not required to use this model in | |
1117 | order to boot the kernel, it is highly encouraged that all SOC | |
1118 | implementations define as complete a flat-device-tree as possible to | |
1119 | describe the devices on the SOC. This will allow for the | |
1120 | genericization of much of the kernel code. | |
1121 | ||
1122 | ||
1123 | 1) Defining child nodes of an SOC | |
1124 | --------------------------------- | |
1125 | ||
1126 | Each device that is part of an SOC may have its own node entry inside | |
1127 | the SOC node. For each device that is included in the SOC, the unit | |
1128 | address property represents the address offset for this device's | |
1129 | memory-mapped registers in the parent's address space. The parent's | |
1130 | address space is defined by the "ranges" property in the top-level soc | |
1131 | node. The "reg" property for each node that exists directly under the | |
1132 | SOC node should contain the address mapping from the child address space | |
1133 | to the parent SOC address space and the size of the device's | |
1134 | memory-mapped register file. | |
1135 | ||
1136 | For many devices that may exist inside an SOC, there are predefined | |
1137 | specifications for the format of the device tree node. All SOC child | |
1138 | nodes should follow these specifications, except where noted in this | |
1139 | document. | |
1140 | ||
1141 | See appendix A for an example partial SOC node definition for the | |
1142 | MPC8540. | |
1143 | ||
1144 | ||
27565903 | 1145 | 2) Representing devices without a current OF specification |
c125a183 DG |
1146 | ---------------------------------------------------------- |
1147 | ||
cf4e5c6e GL |
1148 | Currently, there are many devices on SoCs that do not have a standard |
1149 | representation defined as part of the Open Firmware specifications, | |
1150 | mainly because the boards that contain these SoCs are not currently | |
1151 | booted using Open Firmware. Binding documentation for new devices | |
1152 | should be added to the Documentation/devicetree/bindings directory. | |
1153 | That directory will expand as device tree support is added to more and | |
1154 | more SoCs. | |
1155 | ||
c125a183 | 1156 | |
b053dc5a | 1157 | VII - Specifying interrupt information for devices |
27565903 SY |
1158 | =================================================== |
1159 | ||
cf4e5c6e | 1160 | The device tree represents the buses and devices of a hardware |
27565903 SY |
1161 | system in a form similar to the physical bus topology of the |
1162 | hardware. | |
1163 | ||
1164 | In addition, a logical 'interrupt tree' exists which represents the | |
1165 | hierarchy and routing of interrupts in the hardware. | |
1166 | ||
1167 | The interrupt tree model is fully described in the | |
1168 | document "Open Firmware Recommended Practice: Interrupt | |
1169 | Mapping Version 0.9". The document is available at: | |
1170 | <http://playground.sun.com/1275/practice>. | |
1171 | ||
1172 | 1) interrupts property | |
1173 | ---------------------- | |
1174 | ||
1175 | Devices that generate interrupts to a single interrupt controller | |
1176 | should use the conventional OF representation described in the | |
1177 | OF interrupt mapping documentation. | |
1178 | ||
1179 | Each device which generates interrupts must have an 'interrupt' | |
1180 | property. The interrupt property value is an arbitrary number of | |
1181 | of 'interrupt specifier' values which describe the interrupt or | |
1182 | interrupts for the device. | |
1183 | ||
1184 | The encoding of an interrupt specifier is determined by the | |
1185 | interrupt domain in which the device is located in the | |
1186 | interrupt tree. The root of an interrupt domain specifies in | |
1187 | its #interrupt-cells property the number of 32-bit cells | |
1188 | required to encode an interrupt specifier. See the OF interrupt | |
1189 | mapping documentation for a detailed description of domains. | |
1190 | ||
1191 | For example, the binding for the OpenPIC interrupt controller | |
1192 | specifies an #interrupt-cells value of 2 to encode the interrupt | |
1193 | number and level/sense information. All interrupt children in an | |
1194 | OpenPIC interrupt domain use 2 cells per interrupt in their interrupts | |
1195 | property. | |
1196 | ||
1197 | The PCI bus binding specifies a #interrupt-cell value of 1 to encode | |
1198 | which interrupt pin (INTA,INTB,INTC,INTD) is used. | |
1199 | ||
1200 | 2) interrupt-parent property | |
1201 | ---------------------------- | |
1202 | ||
1203 | The interrupt-parent property is specified to define an explicit | |
1204 | link between a device node and its interrupt parent in | |
1205 | the interrupt tree. The value of interrupt-parent is the | |
1206 | phandle of the parent node. | |
1207 | ||
a33f3224 | 1208 | If the interrupt-parent property is not defined for a node, its |
27565903 SY |
1209 | interrupt parent is assumed to be an ancestor in the node's |
1210 | _device tree_ hierarchy. | |
1211 | ||
1212 | 3) OpenPIC Interrupt Controllers | |
1213 | -------------------------------- | |
1214 | ||
1215 | OpenPIC interrupt controllers require 2 cells to encode | |
1216 | interrupt information. The first cell defines the interrupt | |
1217 | number. The second cell defines the sense and level | |
1218 | information. | |
1219 | ||
1220 | Sense and level information should be encoded as follows: | |
1221 | ||
1222 | 0 = low to high edge sensitive type enabled | |
1223 | 1 = active low level sensitive type enabled | |
1224 | 2 = active high level sensitive type enabled | |
1225 | 3 = high to low edge sensitive type enabled | |
1226 | ||
1227 | 4) ISA Interrupt Controllers | |
1228 | ---------------------------- | |
1229 | ||
1230 | ISA PIC interrupt controllers require 2 cells to encode | |
1231 | interrupt information. The first cell defines the interrupt | |
1232 | number. The second cell defines the sense and level | |
1233 | information. | |
1234 | ||
1235 | ISA PIC interrupt controllers should adhere to the ISA PIC | |
1236 | encodings listed below: | |
1237 | ||
1238 | 0 = active low level sensitive type enabled | |
1239 | 1 = active high level sensitive type enabled | |
1240 | 2 = high to low edge sensitive type enabled | |
1241 | 3 = low to high edge sensitive type enabled | |
1242 | ||
b053dc5a | 1243 | VIII - Specifying Device Power Management Information (sleep property) |
2dff4177 SW |
1244 | =================================================================== |
1245 | ||
1246 | Devices on SOCs often have mechanisms for placing devices into low-power | |
1247 | states that are decoupled from the devices' own register blocks. Sometimes, | |
1248 | this information is more complicated than a cell-index property can | |
1249 | reasonably describe. Thus, each device controlled in such a manner | |
1250 | may contain a "sleep" property which describes these connections. | |
1251 | ||
1252 | The sleep property consists of one or more sleep resources, each of | |
1253 | which consists of a phandle to a sleep controller, followed by a | |
1254 | controller-specific sleep specifier of zero or more cells. | |
1255 | ||
1256 | The semantics of what type of low power modes are possible are defined | |
1257 | by the sleep controller. Some examples of the types of low power modes | |
1258 | that may be supported are: | |
1259 | ||
1260 | - Dynamic: The device may be disabled or enabled at any time. | |
1261 | - System Suspend: The device may request to be disabled or remain | |
1262 | awake during system suspend, but will not be disabled until then. | |
1263 | - Permanent: The device is disabled permanently (until the next hard | |
1264 | reset). | |
1265 | ||
1266 | Some devices may share a clock domain with each other, such that they should | |
1267 | only be suspended when none of the devices are in use. Where reasonable, | |
1268 | such nodes should be placed on a virtual bus, where the bus has the sleep | |
1269 | property. If the clock domain is shared among devices that cannot be | |
1270 | reasonably grouped in this manner, then create a virtual sleep controller | |
1271 | (similar to an interrupt nexus, except that defining a standardized | |
1272 | sleep-map should wait until its necessity is demonstrated). | |
1273 | ||
c125a183 DG |
1274 | Appendix A - Sample SOC node for MPC8540 |
1275 | ======================================== | |
1276 | ||
7e72063c | 1277 | soc@e0000000 { |
c125a183 DG |
1278 | #address-cells = <1>; |
1279 | #size-cells = <1>; | |
7e72063c | 1280 | compatible = "fsl,mpc8540-ccsr", "simple-bus"; |
c125a183 | 1281 | device_type = "soc"; |
7e72063c | 1282 | ranges = <0x00000000 0xe0000000 0x00100000> |
7d4b95ae | 1283 | bus-frequency = <0>; |
7e72063c | 1284 | interrupt-parent = <&pic>; |
c125a183 | 1285 | |
c125a183 | 1286 | ethernet@24000 { |
2dff4177 SW |
1287 | #address-cells = <1>; |
1288 | #size-cells = <1>; | |
c125a183 DG |
1289 | device_type = "network"; |
1290 | model = "TSEC"; | |
2dff4177 | 1291 | compatible = "gianfar", "simple-bus"; |
7e72063c SW |
1292 | reg = <0x24000 0x1000>; |
1293 | local-mac-address = [ 00 E0 0C 00 73 00 ]; | |
1294 | interrupts = <29 2 30 2 34 2>; | |
1295 | phy-handle = <&phy0>; | |
2dff4177 SW |
1296 | sleep = <&pmc 00000080>; |
1297 | ranges; | |
1298 | ||
1299 | mdio@24520 { | |
7e72063c | 1300 | reg = <0x24520 0x20>; |
2dff4177 SW |
1301 | compatible = "fsl,gianfar-mdio"; |
1302 | ||
7e72063c SW |
1303 | phy0: ethernet-phy@0 { |
1304 | interrupts = <5 1>; | |
2dff4177 SW |
1305 | reg = <0>; |
1306 | device_type = "ethernet-phy"; | |
1307 | }; | |
1308 | ||
7e72063c SW |
1309 | phy1: ethernet-phy@1 { |
1310 | interrupts = <5 1>; | |
2dff4177 SW |
1311 | reg = <1>; |
1312 | device_type = "ethernet-phy"; | |
1313 | }; | |
1314 | ||
7e72063c SW |
1315 | phy3: ethernet-phy@3 { |
1316 | interrupts = <7 1>; | |
2dff4177 SW |
1317 | reg = <3>; |
1318 | device_type = "ethernet-phy"; | |
1319 | }; | |
1320 | }; | |
c125a183 DG |
1321 | }; |
1322 | ||
1323 | ethernet@25000 { | |
c125a183 DG |
1324 | device_type = "network"; |
1325 | model = "TSEC"; | |
1326 | compatible = "gianfar"; | |
7e72063c SW |
1327 | reg = <0x25000 0x1000>; |
1328 | local-mac-address = [ 00 E0 0C 00 73 01 ]; | |
1329 | interrupts = <13 2 14 2 18 2>; | |
1330 | phy-handle = <&phy1>; | |
2dff4177 | 1331 | sleep = <&pmc 00000040>; |
c125a183 DG |
1332 | }; |
1333 | ||
1334 | ethernet@26000 { | |
c125a183 DG |
1335 | device_type = "network"; |
1336 | model = "FEC"; | |
1337 | compatible = "gianfar"; | |
7e72063c SW |
1338 | reg = <0x26000 0x1000>; |
1339 | local-mac-address = [ 00 E0 0C 00 73 02 ]; | |
1340 | interrupts = <41 2>; | |
1341 | phy-handle = <&phy3>; | |
2dff4177 | 1342 | sleep = <&pmc 00000020>; |
c125a183 DG |
1343 | }; |
1344 | ||
1345 | serial@4500 { | |
2dff4177 SW |
1346 | #address-cells = <1>; |
1347 | #size-cells = <1>; | |
1348 | compatible = "fsl,mpc8540-duart", "simple-bus"; | |
1349 | sleep = <&pmc 00000002>; | |
1350 | ranges; | |
1351 | ||
1352 | serial@4500 { | |
1353 | device_type = "serial"; | |
1354 | compatible = "ns16550"; | |
7e72063c | 1355 | reg = <0x4500 0x100>; |
2dff4177 | 1356 | clock-frequency = <0>; |
7e72063c | 1357 | interrupts = <42 2>; |
2dff4177 SW |
1358 | }; |
1359 | ||
1360 | serial@4600 { | |
1361 | device_type = "serial"; | |
1362 | compatible = "ns16550"; | |
7e72063c | 1363 | reg = <0x4600 0x100>; |
2dff4177 | 1364 | clock-frequency = <0>; |
7e72063c | 1365 | interrupts = <42 2>; |
2dff4177 | 1366 | }; |
c125a183 DG |
1367 | }; |
1368 | ||
7e72063c | 1369 | pic: pic@40000 { |
c125a183 DG |
1370 | interrupt-controller; |
1371 | #address-cells = <0>; | |
7e72063c SW |
1372 | #interrupt-cells = <2>; |
1373 | reg = <0x40000 0x40000>; | |
c125a183 DG |
1374 | compatible = "chrp,open-pic"; |
1375 | device_type = "open-pic"; | |
c125a183 DG |
1376 | }; |
1377 | ||
1378 | i2c@3000 { | |
7e72063c SW |
1379 | interrupts = <43 2>; |
1380 | reg = <0x3000 0x100>; | |
c125a183 DG |
1381 | compatible = "fsl-i2c"; |
1382 | dfsrr; | |
2dff4177 | 1383 | sleep = <&pmc 00000004>; |
c125a183 DG |
1384 | }; |
1385 | ||
2dff4177 SW |
1386 | pmc: power@e0070 { |
1387 | compatible = "fsl,mpc8540-pmc", "fsl,mpc8548-pmc"; | |
7e72063c | 1388 | reg = <0xe0070 0x20>; |
2dff4177 | 1389 | }; |
c125a183 | 1390 | }; |