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1 | Booting the Linux/ppc kernel without Open Firmware |
2 | -------------------------------------------------- | |
3 | ||
4 | ||
5 | (c) 2005 Benjamin Herrenschmidt <benh at kernel.crashing.org>, | |
6 | IBM Corp. | |
7 | (c) 2005 Becky Bruce <becky.bruce at freescale.com>, | |
8 | Freescale Semiconductor, FSL SOC and 32-bit additions | |
9 | ||
10 | May 18, 2005: Rev 0.1 - Initial draft, no chapter III yet. | |
11 | ||
12 | May 19, 2005: Rev 0.2 - Add chapter III and bits & pieces here or | |
13 | clarifies the fact that a lot of things are | |
14 | optional, the kernel only requires a very | |
15 | small device tree, though it is encouraged | |
16 | to provide an as complete one as possible. | |
17 | ||
18 | May 24, 2005: Rev 0.3 - Precise that DT block has to be in RAM | |
19 | - Misc fixes | |
20 | - Define version 3 and new format version 16 | |
21 | for the DT block (version 16 needs kernel | |
22 | patches, will be fwd separately). | |
23 | String block now has a size, and full path | |
24 | is replaced by unit name for more | |
25 | compactness. | |
26 | linux,phandle is made optional, only nodes | |
27 | that are referenced by other nodes need it. | |
28 | "name" property is now automatically | |
29 | deduced from the unit name | |
30 | ||
31 | June 1, 2005: Rev 0.4 - Correct confusion between OF_DT_END and | |
32 | OF_DT_END_NODE in structure definition. | |
33 | - Change version 16 format to always align | |
34 | property data to 4 bytes. Since tokens are | |
35 | already aligned, that means no specific | |
36 | required alignement between property size | |
37 | and property data. The old style variable | |
38 | alignment would make it impossible to do | |
39 | "simple" insertion of properties using | |
40 | memove (thanks Milton for | |
41 | noticing). Updated kernel patch as well | |
42 | - Correct a few more alignement constraints | |
43 | - Add a chapter about the device-tree | |
44 | compiler and the textural representation of | |
45 | the tree that can be "compiled" by dtc. | |
46 | ||
47 | ||
48 | November 21, 2005: Rev 0.5 | |
49 | - Additions/generalizations for 32-bit | |
50 | - Changed to reflect the new arch/powerpc | |
51 | structure | |
52 | - Added chapter VI | |
53 | ||
54 | ||
55 | ToDo: | |
56 | - Add some definitions of interrupt tree (simple/complex) | |
57 | - Add some definitions for pci host bridges | |
58 | - Add some common address format examples | |
59 | - Add definitions for standard properties and "compatible" | |
60 | names for cells that are not already defined by the existing | |
61 | OF spec. | |
62 | - Compare FSL SOC use of PCI to standard and make sure no new | |
63 | node definition required. | |
64 | - Add more information about node definitions for SOC devices | |
65 | that currently have no standard, like the FSL CPM. | |
66 | ||
67 | ||
68 | I - Introduction | |
69 | ================ | |
70 | ||
71 | During the recent development of the Linux/ppc64 kernel, and more | |
72 | specifically, the addition of new platform types outside of the old | |
73 | IBM pSeries/iSeries pair, it was decided to enforce some strict rules | |
74 | regarding the kernel entry and bootloader <-> kernel interfaces, in | |
75 | order to avoid the degeneration that had become the ppc32 kernel entry | |
76 | point and the way a new platform should be added to the kernel. The | |
77 | legacy iSeries platform breaks those rules as it predates this scheme, | |
78 | but no new board support will be accepted in the main tree that | |
79 | doesn't follows them properly. In addition, since the advent of the | |
80 | arch/powerpc merged architecture for ppc32 and ppc64, new 32-bit | |
81 | platforms and 32-bit platforms which move into arch/powerpc will be | |
82 | required to use these rules as well. | |
83 | ||
84 | The main requirement that will be defined in more detail below is | |
85 | the presence of a device-tree whose format is defined after Open | |
86 | Firmware specification. However, in order to make life easier | |
87 | to embedded board vendors, the kernel doesn't require the device-tree | |
88 | to represent every device in the system and only requires some nodes | |
89 | and properties to be present. This will be described in detail in | |
90 | section III, but, for example, the kernel does not require you to | |
91 | create a node for every PCI device in the system. It is a requirement | |
92 | to have a node for PCI host bridges in order to provide interrupt | |
93 | routing informations and memory/IO ranges, among others. It is also | |
94 | recommended to define nodes for on chip devices and other busses that | |
95 | don't specifically fit in an existing OF specification. This creates a | |
96 | great flexibility in the way the kernel can then probe those and match | |
97 | drivers to device, without having to hard code all sorts of tables. It | |
98 | also makes it more flexible for board vendors to do minor hardware | |
99 | upgrades without significantly impacting the kernel code or cluttering | |
100 | it with special cases. | |
101 | ||
102 | ||
103 | 1) Entry point for arch/powerpc | |
104 | ------------------------------- | |
105 | ||
106 | There is one and one single entry point to the kernel, at the start | |
107 | of the kernel image. That entry point supports two calling | |
108 | conventions: | |
109 | ||
110 | a) Boot from Open Firmware. If your firmware is compatible | |
111 | with Open Firmware (IEEE 1275) or provides an OF compatible | |
112 | client interface API (support for "interpret" callback of | |
113 | forth words isn't required), you can enter the kernel with: | |
114 | ||
115 | r5 : OF callback pointer as defined by IEEE 1275 | |
116 | bindings to powerpc. Only the 32 bit client interface | |
117 | is currently supported | |
118 | ||
119 | r3, r4 : address & length of an initrd if any or 0 | |
120 | ||
121 | The MMU is either on or off; the kernel will run the | |
122 | trampoline located in arch/powerpc/kernel/prom_init.c to | |
123 | extract the device-tree and other information from open | |
124 | firmware and build a flattened device-tree as described | |
125 | in b). prom_init() will then re-enter the kernel using | |
126 | the second method. This trampoline code runs in the | |
127 | context of the firmware, which is supposed to handle all | |
128 | exceptions during that time. | |
129 | ||
130 | b) Direct entry with a flattened device-tree block. This entry | |
131 | point is called by a) after the OF trampoline and can also be | |
132 | called directly by a bootloader that does not support the Open | |
133 | Firmware client interface. It is also used by "kexec" to | |
134 | implement "hot" booting of a new kernel from a previous | |
135 | running one. This method is what I will describe in more | |
136 | details in this document, as method a) is simply standard Open | |
137 | Firmware, and thus should be implemented according to the | |
138 | various standard documents defining it and its binding to the | |
139 | PowerPC platform. The entry point definition then becomes: | |
140 | ||
141 | r3 : physical pointer to the device-tree block | |
142 | (defined in chapter II) in RAM | |
143 | ||
144 | r4 : physical pointer to the kernel itself. This is | |
145 | used by the assembly code to properly disable the MMU | |
146 | in case you are entering the kernel with MMU enabled | |
147 | and a non-1:1 mapping. | |
148 | ||
149 | r5 : NULL (as to differenciate with method a) | |
150 | ||
151 | Note about SMP entry: Either your firmware puts your other | |
152 | CPUs in some sleep loop or spin loop in ROM where you can get | |
153 | them out via a soft reset or some other means, in which case | |
154 | you don't need to care, or you'll have to enter the kernel | |
155 | with all CPUs. The way to do that with method b) will be | |
156 | described in a later revision of this document. | |
157 | ||
158 | ||
159 | 2) Board support | |
160 | ---------------- | |
161 | ||
162 | 64-bit kernels: | |
163 | ||
164 | Board supports (platforms) are not exclusive config options. An | |
165 | arbitrary set of board supports can be built in a single kernel | |
166 | image. The kernel will "know" what set of functions to use for a | |
167 | given platform based on the content of the device-tree. Thus, you | |
168 | should: | |
169 | ||
170 | a) add your platform support as a _boolean_ option in | |
171 | arch/powerpc/Kconfig, following the example of PPC_PSERIES, | |
172 | PPC_PMAC and PPC_MAPLE. The later is probably a good | |
173 | example of a board support to start from. | |
174 | ||
175 | b) create your main platform file as | |
176 | "arch/powerpc/platforms/myplatform/myboard_setup.c" and add it | |
177 | to the Makefile under the condition of your CONFIG_ | |
178 | option. This file will define a structure of type "ppc_md" | |
179 | containing the various callbacks that the generic code will | |
180 | use to get to your platform specific code | |
181 | ||
182 | c) Add a reference to your "ppc_md" structure in the | |
183 | "machines" table in arch/powerpc/kernel/setup_64.c if you are | |
184 | a 64-bit platform. | |
185 | ||
186 | d) request and get assigned a platform number (see PLATFORM_* | |
187 | constants in include/asm-powerpc/processor.h | |
188 | ||
189 | 32-bit embedded kernels: | |
190 | ||
191 | Currently, board support is essentially an exclusive config option. | |
192 | The kernel is configured for a single platform. Part of the reason | |
193 | for this is to keep kernels on embedded systems small and efficient; | |
194 | part of this is due to the fact the code is already that way. In the | |
195 | future, a kernel may support multiple platforms, but only if the | |
196 | platforms feature the same core architectire. A single kernel build | |
197 | cannot support both configurations with Book E and configurations | |
198 | with classic Powerpc architectures. | |
199 | ||
200 | 32-bit embedded platforms that are moved into arch/powerpc using a | |
201 | flattened device tree should adopt the merged tree practice of | |
202 | setting ppc_md up dynamically, even though the kernel is currently | |
203 | built with support for only a single platform at a time. This allows | |
204 | unification of the setup code, and will make it easier to go to a | |
205 | multiple-platform-support model in the future. | |
206 | ||
207 | NOTE: I believe the above will be true once Ben's done with the merge | |
208 | of the boot sequences.... someone speak up if this is wrong! | |
209 | ||
210 | To add a 32-bit embedded platform support, follow the instructions | |
211 | for 64-bit platforms above, with the exception that the Kconfig | |
212 | option should be set up such that the kernel builds exclusively for | |
213 | the platform selected. The processor type for the platform should | |
214 | enable another config option to select the specific board | |
215 | supported. | |
216 | ||
217 | NOTE: If ben doesn't merge the setup files, may need to change this to | |
218 | point to setup_32.c | |
219 | ||
220 | ||
221 | I will describe later the boot process and various callbacks that | |
222 | your platform should implement. | |
223 | ||
224 | ||
225 | II - The DT block format | |
226 | ======================== | |
227 | ||
228 | ||
229 | This chapter defines the actual format of the flattened device-tree | |
230 | passed to the kernel. The actual content of it and kernel requirements | |
231 | are described later. You can find example of code manipulating that | |
232 | format in various places, including arch/powerpc/kernel/prom_init.c | |
233 | which will generate a flattened device-tree from the Open Firmware | |
234 | representation, or the fs2dt utility which is part of the kexec tools | |
235 | which will generate one from a filesystem representation. It is | |
236 | expected that a bootloader like uboot provides a bit more support, | |
237 | that will be discussed later as well. | |
238 | ||
239 | Note: The block has to be in main memory. It has to be accessible in | |
240 | both real mode and virtual mode with no mapping other than main | |
241 | memory. If you are writing a simple flash bootloader, it should copy | |
242 | the block to RAM before passing it to the kernel. | |
243 | ||
244 | ||
245 | 1) Header | |
246 | --------- | |
247 | ||
248 | The kernel is entered with r3 pointing to an area of memory that is | |
249 | roughtly described in include/asm-powerpc/prom.h by the structure | |
250 | boot_param_header: | |
251 | ||
252 | struct boot_param_header { | |
253 | u32 magic; /* magic word OF_DT_HEADER */ | |
254 | u32 totalsize; /* total size of DT block */ | |
255 | u32 off_dt_struct; /* offset to structure */ | |
256 | u32 off_dt_strings; /* offset to strings */ | |
257 | u32 off_mem_rsvmap; /* offset to memory reserve map | |
258 | */ | |
259 | u32 version; /* format version */ | |
260 | u32 last_comp_version; /* last compatible version */ | |
261 | ||
262 | /* version 2 fields below */ | |
263 | u32 boot_cpuid_phys; /* Which physical CPU id we're | |
264 | booting on */ | |
265 | /* version 3 fields below */ | |
266 | u32 size_dt_strings; /* size of the strings block */ | |
267 | }; | |
268 | ||
269 | Along with the constants: | |
270 | ||
271 | /* Definitions used by the flattened device tree */ | |
272 | #define OF_DT_HEADER 0xd00dfeed /* 4: version, | |
273 | 4: total size */ | |
274 | #define OF_DT_BEGIN_NODE 0x1 /* Start node: full name | |
275 | */ | |
276 | #define OF_DT_END_NODE 0x2 /* End node */ | |
277 | #define OF_DT_PROP 0x3 /* Property: name off, | |
278 | size, content */ | |
279 | #define OF_DT_END 0x9 | |
280 | ||
281 | All values in this header are in big endian format, the various | |
282 | fields in this header are defined more precisely below. All | |
283 | "offset" values are in bytes from the start of the header; that is | |
284 | from the value of r3. | |
285 | ||
286 | - magic | |
287 | ||
288 | This is a magic value that "marks" the beginning of the | |
289 | device-tree block header. It contains the value 0xd00dfeed and is | |
290 | defined by the constant OF_DT_HEADER | |
291 | ||
292 | - totalsize | |
293 | ||
294 | This is the total size of the DT block including the header. The | |
295 | "DT" block should enclose all data structures defined in this | |
296 | chapter (who are pointed to by offsets in this header). That is, | |
297 | the device-tree structure, strings, and the memory reserve map. | |
298 | ||
299 | - off_dt_struct | |
300 | ||
301 | This is an offset from the beginning of the header to the start | |
302 | of the "structure" part the device tree. (see 2) device tree) | |
303 | ||
304 | - off_dt_strings | |
305 | ||
306 | This is an offset from the beginning of the header to the start | |
307 | of the "strings" part of the device-tree | |
308 | ||
309 | - off_mem_rsvmap | |
310 | ||
311 | This is an offset from the beginning of the header to the start | |
312 | of the reserved memory map. This map is a list of pairs of 64 | |
313 | bit integers. Each pair is a physical address and a size. The | |
314 | ||
315 | list is terminated by an entry of size 0. This map provides the | |
316 | kernel with a list of physical memory areas that are "reserved" | |
317 | and thus not to be used for memory allocations, especially during | |
318 | early initialization. The kernel needs to allocate memory during | |
319 | boot for things like un-flattening the device-tree, allocating an | |
320 | MMU hash table, etc... Those allocations must be done in such a | |
321 | way to avoid overriding critical things like, on Open Firmware | |
322 | capable machines, the RTAS instance, or on some pSeries, the TCE | |
323 | tables used for the iommu. Typically, the reserve map should | |
324 | contain _at least_ this DT block itself (header,total_size). If | |
325 | you are passing an initrd to the kernel, you should reserve it as | |
326 | well. You do not need to reserve the kernel image itself. The map | |
327 | should be 64 bit aligned. | |
328 | ||
329 | - version | |
330 | ||
331 | This is the version of this structure. Version 1 stops | |
332 | here. Version 2 adds an additional field boot_cpuid_phys. | |
333 | Version 3 adds the size of the strings block, allowing the kernel | |
334 | to reallocate it easily at boot and free up the unused flattened | |
335 | structure after expansion. Version 16 introduces a new more | |
336 | "compact" format for the tree itself that is however not backward | |
337 | compatible. You should always generate a structure of the highest | |
338 | version defined at the time of your implementation. Currently | |
339 | that is version 16, unless you explicitely aim at being backward | |
340 | compatible. | |
341 | ||
342 | - last_comp_version | |
343 | ||
344 | Last compatible version. This indicates down to what version of | |
345 | the DT block you are backward compatible. For example, version 2 | |
346 | is backward compatible with version 1 (that is, a kernel build | |
347 | for version 1 will be able to boot with a version 2 format). You | |
348 | should put a 1 in this field if you generate a device tree of | |
349 | version 1 to 3, or 0x10 if you generate a tree of version 0x10 | |
350 | using the new unit name format. | |
351 | ||
352 | - boot_cpuid_phys | |
353 | ||
354 | This field only exist on version 2 headers. It indicate which | |
355 | physical CPU ID is calling the kernel entry point. This is used, | |
356 | among others, by kexec. If you are on an SMP system, this value | |
357 | should match the content of the "reg" property of the CPU node in | |
358 | the device-tree corresponding to the CPU calling the kernel entry | |
359 | point (see further chapters for more informations on the required | |
360 | device-tree contents) | |
361 | ||
362 | ||
363 | So the typical layout of a DT block (though the various parts don't | |
364 | need to be in that order) looks like this (addresses go from top to | |
365 | bottom): | |
366 | ||
367 | ||
368 | ------------------------------ | |
369 | r3 -> | struct boot_param_header | | |
370 | ------------------------------ | |
371 | | (alignment gap) (*) | | |
372 | ------------------------------ | |
373 | | memory reserve map | | |
374 | ------------------------------ | |
375 | | (alignment gap) | | |
376 | ------------------------------ | |
377 | | | | |
378 | | device-tree structure | | |
379 | | | | |
380 | ------------------------------ | |
381 | | (alignment gap) | | |
382 | ------------------------------ | |
383 | | | | |
384 | | device-tree strings | | |
385 | | | | |
386 | -----> ------------------------------ | |
387 | | | |
388 | | | |
389 | --- (r3 + totalsize) | |
390 | ||
391 | (*) The alignment gaps are not necessarily present; their presence | |
392 | and size are dependent on the various alignment requirements of | |
393 | the individual data blocks. | |
394 | ||
395 | ||
396 | 2) Device tree generalities | |
397 | --------------------------- | |
398 | ||
399 | This device-tree itself is separated in two different blocks, a | |
400 | structure block and a strings block. Both need to be aligned to a 4 | |
401 | byte boundary. | |
402 | ||
403 | First, let's quickly describe the device-tree concept before detailing | |
404 | the storage format. This chapter does _not_ describe the detail of the | |
405 | required types of nodes & properties for the kernel, this is done | |
406 | later in chapter III. | |
407 | ||
408 | The device-tree layout is strongly inherited from the definition of | |
409 | the Open Firmware IEEE 1275 device-tree. It's basically a tree of | |
410 | nodes, each node having two or more named properties. A property can | |
411 | have a value or not. | |
412 | ||
413 | It is a tree, so each node has one and only one parent except for the | |
414 | root node who has no parent. | |
415 | ||
416 | A node has 2 names. The actual node name is generally contained in a | |
417 | property of type "name" in the node property list whose value is a | |
418 | zero terminated string and is mandatory for version 1 to 3 of the | |
419 | format definition (as it is in Open Firmware). Version 0x10 makes it | |
420 | optional as it can generate it from the unit name defined below. | |
421 | ||
422 | There is also a "unit name" that is used to differenciate nodes with | |
423 | the same name at the same level, it is usually made of the node | |
424 | name's, the "@" sign, and a "unit address", which definition is | |
425 | specific to the bus type the node sits on. | |
426 | ||
427 | The unit name doesn't exist as a property per-se but is included in | |
428 | the device-tree structure. It is typically used to represent "path" in | |
429 | the device-tree. More details about the actual format of these will be | |
430 | below. | |
431 | ||
432 | The kernel powerpc generic code does not make any formal use of the | |
433 | unit address (though some board support code may do) so the only real | |
434 | requirement here for the unit address is to ensure uniqueness of | |
435 | the node unit name at a given level of the tree. Nodes with no notion | |
436 | of address and no possible sibling of the same name (like /memory or | |
437 | /cpus) may omit the unit address in the context of this specification, | |
438 | or use the "@0" default unit address. The unit name is used to define | |
439 | a node "full path", which is the concatenation of all parent node | |
440 | unit names separated with "/". | |
441 | ||
442 | The root node doesn't have a defined name, and isn't required to have | |
443 | a name property either if you are using version 3 or earlier of the | |
444 | format. It also has no unit address (no @ symbol followed by a unit | |
445 | address). The root node unit name is thus an empty string. The full | |
446 | path to the root node is "/". | |
447 | ||
448 | Every node which actually represents an actual device (that is, a node | |
449 | which isn't only a virtual "container" for more nodes, like "/cpus" | |
450 | is) is also required to have a "device_type" property indicating the | |
451 | type of node . | |
452 | ||
453 | Finally, every node that can be referenced from a property in another | |
454 | node is required to have a "linux,phandle" property. Real open | |
455 | firmware implementations provide a unique "phandle" value for every | |
456 | node that the "prom_init()" trampoline code turns into | |
457 | "linux,phandle" properties. However, this is made optional if the | |
458 | flattened device tree is used directly. An example of a node | |
459 | referencing another node via "phandle" is when laying out the | |
460 | interrupt tree which will be described in a further version of this | |
461 | document. | |
462 | ||
463 | This "linux, phandle" property is a 32 bit value that uniquely | |
464 | identifies a node. You are free to use whatever values or system of | |
465 | values, internal pointers, or whatever to generate these, the only | |
466 | requirement is that every node for which you provide that property has | |
467 | a unique value for it. | |
468 | ||
469 | Here is an example of a simple device-tree. In this example, an "o" | |
470 | designates a node followed by the node unit name. Properties are | |
471 | presented with their name followed by their content. "content" | |
472 | represents an ASCII string (zero terminated) value, while <content> | |
473 | represents a 32 bit hexadecimal value. The various nodes in this | |
474 | example will be discussed in a later chapter. At this point, it is | |
475 | only meant to give you a idea of what a device-tree looks like. I have | |
476 | purposefully kept the "name" and "linux,phandle" properties which | |
477 | aren't necessary in order to give you a better idea of what the tree | |
478 | looks like in practice. | |
479 | ||
480 | / o device-tree | |
481 | |- name = "device-tree" | |
482 | |- model = "MyBoardName" | |
483 | |- compatible = "MyBoardFamilyName" | |
484 | |- #address-cells = <2> | |
485 | |- #size-cells = <2> | |
486 | |- linux,phandle = <0> | |
487 | | | |
488 | o cpus | |
489 | | | - name = "cpus" | |
490 | | | - linux,phandle = <1> | |
491 | | | - #address-cells = <1> | |
492 | | | - #size-cells = <0> | |
493 | | | | |
494 | | o PowerPC,970@0 | |
495 | | |- name = "PowerPC,970" | |
496 | | |- device_type = "cpu" | |
497 | | |- reg = <0> | |
498 | | |- clock-frequency = <5f5e1000> | |
499 | | |- linux,boot-cpu | |
500 | | |- linux,phandle = <2> | |
501 | | | |
502 | o memory@0 | |
503 | | |- name = "memory" | |
504 | | |- device_type = "memory" | |
505 | | |- reg = <00000000 00000000 00000000 20000000> | |
506 | | |- linux,phandle = <3> | |
507 | | | |
508 | o chosen | |
509 | |- name = "chosen" | |
510 | |- bootargs = "root=/dev/sda2" | |
511 | |- linux,platform = <00000600> | |
512 | |- linux,phandle = <4> | |
513 | ||
514 | This tree is almost a minimal tree. It pretty much contains the | |
515 | minimal set of required nodes and properties to boot a linux kernel; | |
516 | that is, some basic model informations at the root, the CPUs, and the | |
517 | physical memory layout. It also includes misc information passed | |
518 | through /chosen, like in this example, the platform type (mandatory) | |
519 | and the kernel command line arguments (optional). | |
520 | ||
521 | The /cpus/PowerPC,970@0/linux,boot-cpu property is an example of a | |
522 | property without a value. All other properties have a value. The | |
523 | significance of the #address-cells and #size-cells properties will be | |
524 | explained in chapter IV which defines precisely the required nodes and | |
525 | properties and their content. | |
526 | ||
527 | ||
528 | 3) Device tree "structure" block | |
529 | ||
530 | The structure of the device tree is a linearized tree structure. The | |
531 | "OF_DT_BEGIN_NODE" token starts a new node, and the "OF_DT_END_NODE" | |
532 | ends that node definition. Child nodes are simply defined before | |
533 | "OF_DT_END_NODE" (that is nodes within the node). A 'token' is a 32 | |
534 | bit value. The tree has to be "finished" with a OF_DT_END token | |
535 | ||
536 | Here's the basic structure of a single node: | |
537 | ||
538 | * token OF_DT_BEGIN_NODE (that is 0x00000001) | |
539 | * for version 1 to 3, this is the node full path as a zero | |
540 | terminated string, starting with "/". For version 16 and later, | |
541 | this is the node unit name only (or an empty string for the | |
542 | root node) | |
543 | * [align gap to next 4 bytes boundary] | |
544 | * for each property: | |
545 | * token OF_DT_PROP (that is 0x00000003) | |
546 | * 32 bit value of property value size in bytes (or 0 of no | |
547 | * value) | |
548 | * 32 bit value of offset in string block of property name | |
549 | * property value data if any | |
550 | * [align gap to next 4 bytes boundary] | |
551 | * [child nodes if any] | |
552 | * token OF_DT_END_NODE (that is 0x00000002) | |
553 | ||
554 | So the node content can be summmarised as a start token, a full path, | |
555 | a list of properties, a list of child node and an end token. Every | |
556 | child node is a full node structure itself as defined above. | |
557 | ||
558 | 4) Device tree 'strings" block | |
559 | ||
560 | In order to save space, property names, which are generally redundant, | |
561 | are stored separately in the "strings" block. This block is simply the | |
562 | whole bunch of zero terminated strings for all property names | |
563 | concatenated together. The device-tree property definitions in the | |
564 | structure block will contain offset values from the beginning of the | |
565 | strings block. | |
566 | ||
567 | ||
568 | III - Required content of the device tree | |
569 | ========================================= | |
570 | ||
571 | WARNING: All "linux,*" properties defined in this document apply only | |
572 | to a flattened device-tree. If your platform uses a real | |
573 | implementation of Open Firmware or an implementation compatible with | |
574 | the Open Firmware client interface, those properties will be created | |
575 | by the trampoline code in the kernel's prom_init() file. For example, | |
576 | that's where you'll have to add code to detect your board model and | |
577 | set the platform number. However, when using the flatenned device-tree | |
578 | entry point, there is no prom_init() pass, and thus you have to | |
579 | provide those properties yourself. | |
580 | ||
581 | ||
582 | 1) Note about cells and address representation | |
583 | ---------------------------------------------- | |
584 | ||
585 | The general rule is documented in the various Open Firmware | |
586 | documentations. If you chose to describe a bus with the device-tree | |
587 | and there exist an OF bus binding, then you should follow the | |
588 | specification. However, the kernel does not require every single | |
589 | device or bus to be described by the device tree. | |
590 | ||
591 | In general, the format of an address for a device is defined by the | |
592 | parent bus type, based on the #address-cells and #size-cells | |
593 | property. In the absence of such a property, the parent's parent | |
594 | values are used, etc... The kernel requires the root node to have | |
595 | those properties defining addresses format for devices directly mapped | |
596 | on the processor bus. | |
597 | ||
598 | Those 2 properties define 'cells' for representing an address and a | |
599 | size. A "cell" is a 32 bit number. For example, if both contain 2 | |
600 | like the example tree given above, then an address and a size are both | |
601 | composed of 2 cells, and each is a 64 bit number (cells are | |
602 | concatenated and expected to be in big endian format). Another example | |
603 | is the way Apple firmware defines them, with 2 cells for an address | |
604 | and one cell for a size. Most 32-bit implementations should define | |
605 | #address-cells and #size-cells to 1, which represents a 32-bit value. | |
606 | Some 32-bit processors allow for physical addresses greater than 32 | |
607 | bits; these processors should define #address-cells as 2. | |
608 | ||
609 | "reg" properties are always a tuple of the type "address size" where | |
610 | the number of cells of address and size is specified by the bus | |
611 | #address-cells and #size-cells. When a bus supports various address | |
612 | spaces and other flags relative to a given address allocation (like | |
613 | prefetchable, etc...) those flags are usually added to the top level | |
614 | bits of the physical address. For example, a PCI physical address is | |
615 | made of 3 cells, the bottom two containing the actual address itself | |
616 | while the top cell contains address space indication, flags, and pci | |
617 | bus & device numbers. | |
618 | ||
619 | For busses that support dynamic allocation, it's the accepted practice | |
620 | to then not provide the address in "reg" (keep it 0) though while | |
621 | providing a flag indicating the address is dynamically allocated, and | |
622 | then, to provide a separate "assigned-addresses" property that | |
623 | contains the fully allocated addresses. See the PCI OF bindings for | |
624 | details. | |
625 | ||
626 | In general, a simple bus with no address space bits and no dynamic | |
627 | allocation is preferred if it reflects your hardware, as the existing | |
628 | kernel address parsing functions will work out of the box. If you | |
629 | define a bus type with a more complex address format, including things | |
630 | like address space bits, you'll have to add a bus translator to the | |
631 | prom_parse.c file of the recent kernels for your bus type. | |
632 | ||
633 | The "reg" property only defines addresses and sizes (if #size-cells | |
634 | is | |
635 | non-0) within a given bus. In order to translate addresses upward | |
636 | (that is into parent bus addresses, and possibly into cpu physical | |
637 | addresses), all busses must contain a "ranges" property. If the | |
638 | "ranges" property is missing at a given level, it's assumed that | |
639 | translation isn't possible. The format of the "ranges" proprety for a | |
640 | bus is a list of: | |
641 | ||
642 | bus address, parent bus address, size | |
643 | ||
644 | "bus address" is in the format of the bus this bus node is defining, | |
645 | that is, for a PCI bridge, it would be a PCI address. Thus, (bus | |
646 | address, size) defines a range of addresses for child devices. "parent | |
647 | bus address" is in the format of the parent bus of this bus. For | |
648 | example, for a PCI host controller, that would be a CPU address. For a | |
649 | PCI<->ISA bridge, that would be a PCI address. It defines the base | |
650 | address in the parent bus where the beginning of that range is mapped. | |
651 | ||
652 | For a new 64 bit powerpc board, I recommend either the 2/2 format or | |
653 | Apple's 2/1 format which is slightly more compact since sizes usually | |
654 | fit in a single 32 bit word. New 32 bit powerpc boards should use a | |
655 | 1/1 format, unless the processor supports physical addresses greater | |
656 | than 32-bits, in which case a 2/1 format is recommended. | |
657 | ||
658 | ||
659 | 2) Note about "compatible" properties | |
660 | ------------------------------------- | |
661 | ||
662 | These properties are optional, but recommended in devices and the root | |
663 | node. The format of a "compatible" property is a list of concatenated | |
664 | zero terminated strings. They allow a device to express its | |
665 | compatibility with a family of similar devices, in some cases, | |
666 | allowing a single driver to match against several devices regardless | |
667 | of their actual names. | |
668 | ||
669 | 3) Note about "name" properties | |
670 | ------------------------------- | |
671 | ||
672 | While earlier users of Open Firmware like OldWorld macintoshes tended | |
673 | to use the actual device name for the "name" property, it's nowadays | |
674 | considered a good practice to use a name that is closer to the device | |
675 | class (often equal to device_type). For example, nowadays, ethernet | |
676 | controllers are named "ethernet", an additional "model" property | |
677 | defining precisely the chip type/model, and "compatible" property | |
678 | defining the family in case a single driver can driver more than one | |
679 | of these chips. However, the kernel doesn't generally put any | |
680 | restriction on the "name" property; it is simply considered good | |
681 | practice to follow the standard and its evolutions as closely as | |
682 | possible. | |
683 | ||
684 | Note also that the new format version 16 makes the "name" property | |
685 | optional. If it's absent for a node, then the node's unit name is then | |
686 | used to reconstruct the name. That is, the part of the unit name | |
687 | before the "@" sign is used (or the entire unit name if no "@" sign | |
688 | is present). | |
689 | ||
690 | 4) Note about node and property names and character set | |
691 | ------------------------------------------------------- | |
692 | ||
693 | While open firmware provides more flexibe usage of 8859-1, this | |
694 | specification enforces more strict rules. Nodes and properties should | |
695 | be comprised only of ASCII characters 'a' to 'z', '0' to | |
696 | '9', ',', '.', '_', '+', '#', '?', and '-'. Node names additionally | |
697 | allow uppercase characters 'A' to 'Z' (property names should be | |
698 | lowercase. The fact that vendors like Apple don't respect this rule is | |
699 | irrelevant here). Additionally, node and property names should always | |
700 | begin with a character in the range 'a' to 'z' (or 'A' to 'Z' for node | |
701 | names). | |
702 | ||
703 | The maximum number of characters for both nodes and property names | |
704 | is 31. In the case of node names, this is only the leftmost part of | |
705 | a unit name (the pure "name" property), it doesn't include the unit | |
706 | address which can extend beyond that limit. | |
707 | ||
708 | ||
709 | 5) Required nodes and properties | |
710 | -------------------------------- | |
711 | These are all that are currently required. However, it is strongly | |
712 | recommended that you expose PCI host bridges as documented in the | |
713 | PCI binding to open firmware, and your interrupt tree as documented | |
714 | in OF interrupt tree specification. | |
715 | ||
716 | a) The root node | |
717 | ||
718 | The root node requires some properties to be present: | |
719 | ||
720 | - model : this is your board name/model | |
721 | - #address-cells : address representation for "root" devices | |
722 | - #size-cells: the size representation for "root" devices | |
723 | ||
724 | Additionally, some recommended properties are: | |
725 | ||
726 | - compatible : the board "family" generally finds its way here, | |
727 | for example, if you have 2 board models with a similar layout, | |
728 | that typically get driven by the same platform code in the | |
729 | kernel, you would use a different "model" property but put a | |
730 | value in "compatible". The kernel doesn't directly use that | |
731 | value (see /chosen/linux,platform for how the kernel choses a | |
732 | platform type) but it is generally useful. | |
733 | ||
734 | The root node is also generally where you add additional properties | |
735 | specific to your board like the serial number if any, that sort of | |
736 | thing. it is recommended that if you add any "custom" property whose | |
737 | name may clash with standard defined ones, you prefix them with your | |
738 | vendor name and a comma. | |
739 | ||
740 | b) The /cpus node | |
741 | ||
742 | This node is the parent of all individual CPU nodes. It doesn't | |
743 | have any specific requirements, though it's generally good practice | |
744 | to have at least: | |
745 | ||
746 | #address-cells = <00000001> | |
747 | #size-cells = <00000000> | |
748 | ||
749 | This defines that the "address" for a CPU is a single cell, and has | |
750 | no meaningful size. This is not necessary but the kernel will assume | |
751 | that format when reading the "reg" properties of a CPU node, see | |
752 | below | |
753 | ||
754 | c) The /cpus/* nodes | |
755 | ||
756 | So under /cpus, you are supposed to create a node for every CPU on | |
757 | the machine. There is no specific restriction on the name of the | |
758 | CPU, though It's common practice to call it PowerPC,<name>. For | |
759 | example, Apple uses PowerPC,G5 while IBM uses PowerPC,970FX. | |
760 | ||
761 | Required properties: | |
762 | ||
763 | - device_type : has to be "cpu" | |
764 | - reg : This is the physical cpu number, it's a single 32 bit cell | |
765 | and is also used as-is as the unit number for constructing the | |
766 | unit name in the full path. For example, with 2 CPUs, you would | |
767 | have the full path: | |
768 | /cpus/PowerPC,970FX@0 | |
769 | /cpus/PowerPC,970FX@1 | |
770 | (unit addresses do not require leading zeroes) | |
771 | - d-cache-line-size : one cell, L1 data cache line size in bytes | |
772 | - i-cache-line-size : one cell, L1 instruction cache line size in | |
773 | bytes | |
774 | - d-cache-size : one cell, size of L1 data cache in bytes | |
775 | - i-cache-size : one cell, size of L1 instruction cache in bytes | |
776 | - linux, boot-cpu : Should be defined if this cpu is the boot cpu. | |
777 | ||
778 | Recommended properties: | |
779 | ||
780 | - timebase-frequency : a cell indicating the frequency of the | |
781 | timebase in Hz. This is not directly used by the generic code, | |
782 | but you are welcome to copy/paste the pSeries code for setting | |
783 | the kernel timebase/decrementer calibration based on this | |
784 | value. | |
785 | - clock-frequency : a cell indicating the CPU core clock frequency | |
786 | in Hz. A new property will be defined for 64 bit values, but if | |
787 | your frequency is < 4Ghz, one cell is enough. Here as well as | |
788 | for the above, the common code doesn't use that property, but | |
789 | you are welcome to re-use the pSeries or Maple one. A future | |
790 | kernel version might provide a common function for this. | |
791 | ||
792 | You are welcome to add any property you find relevant to your board, | |
793 | like some information about the mechanism used to soft-reset the | |
794 | CPUs. For example, Apple puts the GPIO number for CPU soft reset | |
795 | lines in there as a "soft-reset" property since they start secondary | |
796 | CPUs by soft-resetting them. | |
797 | ||
798 | ||
799 | d) the /memory node(s) | |
800 | ||
801 | To define the physical memory layout of your board, you should | |
802 | create one or more memory node(s). You can either create a single | |
803 | node with all memory ranges in its reg property, or you can create | |
804 | several nodes, as you wish. The unit address (@ part) used for the | |
805 | full path is the address of the first range of memory defined by a | |
806 | given node. If you use a single memory node, this will typically be | |
807 | @0. | |
808 | ||
809 | Required properties: | |
810 | ||
811 | - device_type : has to be "memory" | |
812 | - reg : This property contains all the physical memory ranges of | |
813 | your board. It's a list of addresses/sizes concatenated | |
814 | together, with the number of cells of each defined by the | |
815 | #address-cells and #size-cells of the root node. For example, | |
816 | with both of these properties beeing 2 like in the example given | |
817 | earlier, a 970 based machine with 6Gb of RAM could typically | |
818 | have a "reg" property here that looks like: | |
819 | ||
820 | 00000000 00000000 00000000 80000000 | |
821 | 00000001 00000000 00000001 00000000 | |
822 | ||
823 | That is a range starting at 0 of 0x80000000 bytes and a range | |
824 | starting at 0x100000000 and of 0x100000000 bytes. You can see | |
825 | that there is no memory covering the IO hole between 2Gb and | |
826 | 4Gb. Some vendors prefer splitting those ranges into smaller | |
827 | segments, but the kernel doesn't care. | |
828 | ||
829 | e) The /chosen node | |
830 | ||
831 | This node is a bit "special". Normally, that's where open firmware | |
832 | puts some variable environment information, like the arguments, or | |
833 | phandle pointers to nodes like the main interrupt controller, or the | |
834 | default input/output devices. | |
835 | ||
836 | This specification makes a few of these mandatory, but also defines | |
837 | some linux-specific properties that would be normally constructed by | |
838 | the prom_init() trampoline when booting with an OF client interface, | |
839 | but that you have to provide yourself when using the flattened format. | |
840 | ||
841 | Required properties: | |
842 | ||
843 | - linux,platform : This is your platform number as assigned by the | |
844 | architecture maintainers | |
845 | ||
846 | Recommended properties: | |
847 | ||
848 | - bootargs : This zero-terminated string is passed as the kernel | |
849 | command line | |
850 | - linux,stdout-path : This is the full path to your standard | |
851 | console device if any. Typically, if you have serial devices on | |
852 | your board, you may want to put the full path to the one set as | |
853 | the default console in the firmware here, for the kernel to pick | |
854 | it up as it's own default console. If you look at the funciton | |
855 | set_preferred_console() in arch/ppc64/kernel/setup.c, you'll see | |
856 | that the kernel tries to find out the default console and has | |
857 | knowledge of various types like 8250 serial ports. You may want | |
858 | to extend this function to add your own. | |
859 | - interrupt-controller : This is one cell containing a phandle | |
860 | value that matches the "linux,phandle" property of your main | |
861 | interrupt controller node. May be used for interrupt routing. | |
862 | ||
863 | ||
864 | Note that u-boot creates and fills in the chosen node for platforms | |
865 | that use it. | |
866 | ||
867 | f) the /soc<SOCname> node | |
868 | ||
869 | This node is used to represent a system-on-a-chip (SOC) and must be | |
870 | present if the processor is a SOC. The top-level soc node contains | |
871 | information that is global to all devices on the SOC. The node name | |
872 | should contain a unit address for the SOC, which is the base address | |
873 | of the memory-mapped register set for the SOC. The name of an soc | |
874 | node should start with "soc", and the remainder of the name should | |
875 | represent the part number for the soc. For example, the MPC8540's | |
876 | soc node would be called "soc8540". | |
877 | ||
878 | Required properties: | |
879 | ||
880 | - device_type : Should be "soc" | |
881 | - ranges : Should be defined as specified in 1) to describe the | |
882 | translation of SOC addresses for memory mapped SOC registers. | |
883 | ||
884 | Recommended properties: | |
885 | ||
886 | - reg : This property defines the address and size of the | |
887 | memory-mapped registers that are used for the SOC node itself. | |
888 | It does not include the child device registers - these will be | |
889 | defined inside each child node. The address specified in the | |
890 | "reg" property should match the unit address of the SOC node. | |
891 | - #address-cells : Address representation for "soc" devices. The | |
892 | format of this field may vary depending on whether or not the | |
893 | device registers are memory mapped. For memory mapped | |
894 | registers, this field represents the number of cells needed to | |
895 | represent the address of the registers. For SOCs that do not | |
896 | use MMIO, a special address format should be defined that | |
897 | contains enough cells to represent the required information. | |
898 | See 1) above for more details on defining #address-cells. | |
899 | - #size-cells : Size representation for "soc" devices | |
900 | - #interrupt-cells : Defines the width of cells used to represent | |
901 | interrupts. Typically this value is <2>, which includes a | |
902 | 32-bit number that represents the interrupt number, and a | |
903 | 32-bit number that represents the interrupt sense and level. | |
904 | This field is only needed if the SOC contains an interrupt | |
905 | controller. | |
906 | ||
907 | The SOC node may contain child nodes for each SOC device that the | |
908 | platform uses. Nodes should not be created for devices which exist | |
909 | on the SOC but are not used by a particular platform. See chapter VI | |
910 | for more information on how to specify devices that are part of an | |
911 | SOC. | |
912 | ||
913 | Example SOC node for the MPC8540: | |
914 | ||
915 | soc8540@e0000000 { | |
916 | #address-cells = <1>; | |
917 | #size-cells = <1>; | |
918 | #interrupt-cells = <2>; | |
919 | device_type = "soc"; | |
920 | ranges = <00000000 e0000000 00100000> | |
921 | reg = <e0000000 00003000>; | |
922 | } | |
923 | ||
924 | ||
925 | ||
926 | IV - "dtc", the device tree compiler | |
927 | ==================================== | |
928 | ||
929 | ||
930 | dtc source code can be found at | |
931 | <http://ozlabs.org/~dgibson/dtc/dtc.tar.gz> | |
932 | ||
933 | WARNING: This version is still in early development stage; the | |
934 | resulting device-tree "blobs" have not yet been validated with the | |
935 | kernel. The current generated bloc lacks a useful reserve map (it will | |
936 | be fixed to generate an empty one, it's up to the bootloader to fill | |
937 | it up) among others. The error handling needs work, bugs are lurking, | |
938 | etc... | |
939 | ||
940 | dtc basically takes a device-tree in a given format and outputs a | |
941 | device-tree in another format. The currently supported formats are: | |
942 | ||
943 | Input formats: | |
944 | ------------- | |
945 | ||
946 | - "dtb": "blob" format, that is a flattened device-tree block | |
947 | with | |
948 | header all in a binary blob. | |
949 | - "dts": "source" format. This is a text file containing a | |
950 | "source" for a device-tree. The format is defined later in this | |
951 | chapter. | |
952 | - "fs" format. This is a representation equivalent to the | |
953 | output of /proc/device-tree, that is nodes are directories and | |
954 | properties are files | |
955 | ||
956 | Output formats: | |
957 | --------------- | |
958 | ||
959 | - "dtb": "blob" format | |
960 | - "dts": "source" format | |
961 | - "asm": assembly language file. This is a file that can be | |
962 | sourced by gas to generate a device-tree "blob". That file can | |
963 | then simply be added to your Makefile. Additionally, the | |
964 | assembly file exports some symbols that can be use | |
965 | ||
966 | ||
967 | The syntax of the dtc tool is | |
968 | ||
969 | dtc [-I <input-format>] [-O <output-format>] | |
970 | [-o output-filename] [-V output_version] input_filename | |
971 | ||
972 | ||
973 | The "output_version" defines what versio of the "blob" format will be | |
974 | generated. Supported versions are 1,2,3 and 16. The default is | |
975 | currently version 3 but that may change in the future to version 16. | |
976 | ||
977 | Additionally, dtc performs various sanity checks on the tree, like the | |
978 | uniqueness of linux,phandle properties, validity of strings, etc... | |
979 | ||
980 | The format of the .dts "source" file is "C" like, supports C and C++ | |
981 | style commments. | |
982 | ||
983 | / { | |
984 | } | |
985 | ||
986 | The above is the "device-tree" definition. It's the only statement | |
987 | supported currently at the toplevel. | |
988 | ||
989 | / { | |
990 | property1 = "string_value"; /* define a property containing a 0 | |
991 | * terminated string | |
992 | */ | |
993 | ||
994 | property2 = <1234abcd>; /* define a property containing a | |
995 | * numerical 32 bits value (hexadecimal) | |
996 | */ | |
997 | ||
998 | property3 = <12345678 12345678 deadbeef>; | |
999 | /* define a property containing 3 | |
1000 | * numerical 32 bits values (cells) in | |
1001 | * hexadecimal | |
1002 | */ | |
1003 | property4 = [0a 0b 0c 0d de ea ad be ef]; | |
1004 | /* define a property whose content is | |
1005 | * an arbitrary array of bytes | |
1006 | */ | |
1007 | ||
1008 | childnode@addresss { /* define a child node named "childnode" | |
1009 | * whose unit name is "childnode at | |
1010 | * address" | |
1011 | */ | |
1012 | ||
1013 | childprop = "hello\n"; /* define a property "childprop" of | |
1014 | * childnode (in this case, a string) | |
1015 | */ | |
1016 | }; | |
1017 | }; | |
1018 | ||
1019 | Nodes can contain other nodes etc... thus defining the hierarchical | |
1020 | structure of the tree. | |
1021 | ||
1022 | Strings support common escape sequences from C: "\n", "\t", "\r", | |
1023 | "\(octal value)", "\x(hex value)". | |
1024 | ||
1025 | It is also suggested that you pipe your source file through cpp (gcc | |
1026 | preprocessor) so you can use #include's, #define for constants, etc... | |
1027 | ||
1028 | Finally, various options are planned but not yet implemented, like | |
1029 | automatic generation of phandles, labels (exported to the asm file so | |
1030 | you can point to a property content and change it easily from whatever | |
1031 | you link the device-tree with), label or path instead of numeric value | |
1032 | in some cells to "point" to a node (replaced by a phandle at compile | |
1033 | time), export of reserve map address to the asm file, ability to | |
1034 | specify reserve map content at compile time, etc... | |
1035 | ||
1036 | We may provide a .h include file with common definitions of that | |
1037 | proves useful for some properties (like building PCI properties or | |
1038 | interrupt maps) though it may be better to add a notion of struct | |
1039 | definitions to the compiler... | |
1040 | ||
1041 | ||
1042 | V - Recommendations for a bootloader | |
1043 | ==================================== | |
1044 | ||
1045 | ||
1046 | Here are some various ideas/recommendations that have been proposed | |
1047 | while all this has been defined and implemented. | |
1048 | ||
1049 | - The bootloader may want to be able to use the device-tree itself | |
1050 | and may want to manipulate it (to add/edit some properties, | |
1051 | like physical memory size or kernel arguments). At this point, 2 | |
1052 | choices can be made. Either the bootloader works directly on the | |
1053 | flattened format, or the bootloader has its own internal tree | |
1054 | representation with pointers (similar to the kernel one) and | |
1055 | re-flattens the tree when booting the kernel. The former is a bit | |
1056 | more difficult to edit/modify, the later requires probably a bit | |
1057 | more code to handle the tree structure. Note that the structure | |
1058 | format has been designed so it's relatively easy to "insert" | |
1059 | properties or nodes or delete them by just memmoving things | |
1060 | around. It contains no internal offsets or pointers for this | |
1061 | purpose. | |
1062 | ||
1063 | - An example of code for iterating nodes & retreiving properties | |
1064 | directly from the flattened tree format can be found in the kernel | |
1065 | file arch/ppc64/kernel/prom.c, look at scan_flat_dt() function, | |
1066 | it's usage in early_init_devtree(), and the corresponding various | |
1067 | early_init_dt_scan_*() callbacks. That code can be re-used in a | |
1068 | GPL bootloader, and as the author of that code, I would be happy | |
1069 | do discuss possible free licencing to any vendor who wishes to | |
1070 | integrate all or part of this code into a non-GPL bootloader. | |
1071 | ||
1072 | ||
1073 | ||
1074 | VI - System-on-a-chip devices and nodes | |
1075 | ======================================= | |
1076 | ||
1077 | Many companies are now starting to develop system-on-a-chip | |
1078 | processors, where the processor core (cpu) and many peripheral devices | |
1079 | exist on a single piece of silicon. For these SOCs, an SOC node | |
1080 | should be used that defines child nodes for the devices that make | |
1081 | up the SOC. While platforms are not required to use this model in | |
1082 | order to boot the kernel, it is highly encouraged that all SOC | |
1083 | implementations define as complete a flat-device-tree as possible to | |
1084 | describe the devices on the SOC. This will allow for the | |
1085 | genericization of much of the kernel code. | |
1086 | ||
1087 | ||
1088 | 1) Defining child nodes of an SOC | |
1089 | --------------------------------- | |
1090 | ||
1091 | Each device that is part of an SOC may have its own node entry inside | |
1092 | the SOC node. For each device that is included in the SOC, the unit | |
1093 | address property represents the address offset for this device's | |
1094 | memory-mapped registers in the parent's address space. The parent's | |
1095 | address space is defined by the "ranges" property in the top-level soc | |
1096 | node. The "reg" property for each node that exists directly under the | |
1097 | SOC node should contain the address mapping from the child address space | |
1098 | to the parent SOC address space and the size of the device's | |
1099 | memory-mapped register file. | |
1100 | ||
1101 | For many devices that may exist inside an SOC, there are predefined | |
1102 | specifications for the format of the device tree node. All SOC child | |
1103 | nodes should follow these specifications, except where noted in this | |
1104 | document. | |
1105 | ||
1106 | See appendix A for an example partial SOC node definition for the | |
1107 | MPC8540. | |
1108 | ||
1109 | ||
1110 | 2) Specifying interrupt information for SOC devices | |
1111 | --------------------------------------------------- | |
1112 | ||
1113 | Each device that is part of an SOC and which generates interrupts | |
1114 | should have the following properties: | |
1115 | ||
1116 | - interrupt-parent : contains the phandle of the interrupt | |
1117 | controller which handles interrupts for this device | |
1118 | - interrupts : a list of tuples representing the interrupt | |
1119 | number and the interrupt sense and level for each interupt | |
1120 | for this device. | |
1121 | ||
1122 | This information is used by the kernel to build the interrupt table | |
1123 | for the interrupt controllers in the system. | |
1124 | ||
1125 | Sense and level information should be encoded as follows: | |
1126 | ||
1127 | Devices connected to openPIC-compatible controllers should encode | |
1128 | sense and polarity as follows: | |
1129 | ||
1130 | 0 = high to low edge sensitive type enabled | |
1131 | 1 = active low level sensitive type enabled | |
1132 | 2 = low to high edge sensitive type enabled | |
1133 | 3 = active high level sensitive type enabled | |
1134 | ||
1135 | ISA PIC interrupt controllers should adhere to the ISA PIC | |
1136 | encodings listed below: | |
1137 | ||
1138 | 0 = active low level sensitive type enabled | |
1139 | 1 = active high level sensitive type enabled | |
1140 | 2 = high to low edge sensitive type enabled | |
1141 | 3 = low to high edge sensitive type enabled | |
1142 | ||
1143 | ||
1144 | ||
1145 | 3) Representing devices without a current OF specification | |
1146 | ---------------------------------------------------------- | |
1147 | ||
1148 | Currently, there are many devices on SOCs that do not have a standard | |
1149 | representation pre-defined as part of the open firmware | |
1150 | specifications, mainly because the boards that contain these SOCs are | |
1151 | not currently booted using open firmware. This section contains | |
1152 | descriptions for the SOC devices for which new nodes have been | |
1153 | defined; this list will expand as more and more SOC-containing | |
1154 | platforms are moved over to use the flattened-device-tree model. | |
1155 | ||
1156 | a) MDIO IO device | |
1157 | ||
1158 | The MDIO is a bus to which the PHY devices are connected. For each | |
1159 | device that exists on this bus, a child node should be created. See | |
1160 | the definition of the PHY node below for an example of how to define | |
1161 | a PHY. | |
1162 | ||
1163 | Required properties: | |
1164 | - reg : Offset and length of the register set for the device | |
1165 | - device_type : Should be "mdio" | |
1166 | - compatible : Should define the compatible device type for the | |
1167 | mdio. Currently, this is most likely to be "gianfar" | |
1168 | ||
1169 | Example: | |
1170 | ||
1171 | mdio@24520 { | |
1172 | reg = <24520 20>; | |
1173 | ||
1174 | ethernet-phy@0 { | |
1175 | ...... | |
1176 | }; | |
1177 | }; | |
1178 | ||
1179 | ||
1180 | b) Gianfar-compatible ethernet nodes | |
1181 | ||
1182 | Required properties: | |
1183 | ||
1184 | - device_type : Should be "network" | |
1185 | - model : Model of the device. Can be "TSEC", "eTSEC", or "FEC" | |
1186 | - compatible : Should be "gianfar" | |
1187 | - reg : Offset and length of the register set for the device | |
1188 | - address : List of bytes representing the ethernet address of | |
1189 | this controller | |
1190 | - interrupts : <a b> where a is the interrupt number and b is a | |
1191 | field that represents an encoding of the sense and level | |
1192 | information for the interrupt. This should be encoded based on | |
1193 | the information in section 2) depending on the type of interrupt | |
1194 | controller you have. | |
1195 | - interrupt-parent : the phandle for the interrupt controller that | |
1196 | services interrupts for this device. | |
1197 | - phy-handle : The phandle for the PHY connected to this ethernet | |
1198 | controller. | |
1199 | ||
1200 | Example: | |
1201 | ||
1202 | ethernet@24000 { | |
1203 | #size-cells = <0>; | |
1204 | device_type = "network"; | |
1205 | model = "TSEC"; | |
1206 | compatible = "gianfar"; | |
1207 | reg = <24000 1000>; | |
1208 | address = [ 00 E0 0C 00 73 00 ]; | |
1209 | interrupts = <d 3 e 3 12 3>; | |
1210 | interrupt-parent = <40000>; | |
1211 | phy-handle = <2452000> | |
1212 | }; | |
1213 | ||
1214 | ||
1215 | ||
1216 | c) PHY nodes | |
1217 | ||
1218 | Required properties: | |
1219 | ||
1220 | - device_type : Should be "ethernet-phy" | |
1221 | - interrupts : <a b> where a is the interrupt number and b is a | |
1222 | field that represents an encoding of the sense and level | |
1223 | information for the interrupt. This should be encoded based on | |
1224 | the information in section 2) depending on the type of interrupt | |
1225 | controller you have. | |
1226 | - interrupt-parent : the phandle for the interrupt controller that | |
1227 | services interrupts for this device. | |
1228 | - reg : The ID number for the phy, usually a small integer | |
1229 | - linux,phandle : phandle for this node; likely referenced by an | |
1230 | ethernet controller node. | |
1231 | ||
1232 | ||
1233 | Example: | |
1234 | ||
1235 | ethernet-phy@0 { | |
1236 | linux,phandle = <2452000> | |
1237 | interrupt-parent = <40000>; | |
1238 | interrupts = <35 1>; | |
1239 | reg = <0>; | |
1240 | device_type = "ethernet-phy"; | |
1241 | }; | |
1242 | ||
1243 | ||
1244 | d) Interrupt controllers | |
1245 | ||
1246 | Some SOC devices contain interrupt controllers that are different | |
1247 | from the standard Open PIC specification. The SOC device nodes for | |
1248 | these types of controllers should be specified just like a standard | |
1249 | OpenPIC controller. Sense and level information should be encoded | |
1250 | as specified in section 2) of this chapter for each device that | |
1251 | specifies an interrupt. | |
1252 | ||
1253 | Example : | |
1254 | ||
1255 | pic@40000 { | |
1256 | linux,phandle = <40000>; | |
1257 | clock-frequency = <0>; | |
1258 | interrupt-controller; | |
1259 | #address-cells = <0>; | |
1260 | reg = <40000 40000>; | |
1261 | built-in; | |
1262 | compatible = "chrp,open-pic"; | |
1263 | device_type = "open-pic"; | |
1264 | big-endian; | |
1265 | }; | |
1266 | ||
1267 | ||
1268 | e) I2C | |
1269 | ||
1270 | Required properties : | |
1271 | ||
1272 | - device_type : Should be "i2c" | |
1273 | - reg : Offset and length of the register set for the device | |
1274 | ||
1275 | Recommended properties : | |
1276 | ||
1277 | - compatible : Should be "fsl-i2c" for parts compatible with | |
1278 | Freescale I2C specifications. | |
1279 | - interrupts : <a b> where a is the interrupt number and b is a | |
1280 | field that represents an encoding of the sense and level | |
1281 | information for the interrupt. This should be encoded based on | |
1282 | the information in section 2) depending on the type of interrupt | |
1283 | controller you have. | |
1284 | - interrupt-parent : the phandle for the interrupt controller that | |
1285 | services interrupts for this device. | |
1286 | - dfsrr : boolean; if defined, indicates that this I2C device has | |
1287 | a digital filter sampling rate register | |
1288 | - fsl5200-clocking : boolean; if defined, indicated that this device | |
1289 | uses the FSL 5200 clocking mechanism. | |
1290 | ||
1291 | Example : | |
1292 | ||
1293 | i2c@3000 { | |
1294 | interrupt-parent = <40000>; | |
1295 | interrupts = <1b 3>; | |
1296 | reg = <3000 18>; | |
1297 | device_type = "i2c"; | |
1298 | compatible = "fsl-i2c"; | |
1299 | dfsrr; | |
1300 | }; | |
1301 | ||
1302 | ||
1303 | More devices will be defined as this spec matures. | |
1304 | ||
1305 | ||
1306 | Appendix A - Sample SOC node for MPC8540 | |
1307 | ======================================== | |
1308 | ||
1309 | Note that the #address-cells and #size-cells for the SoC node | |
1310 | in this example have been explicitly listed; these are likely | |
1311 | not necessary as they are usually the same as the root node. | |
1312 | ||
1313 | soc8540@e0000000 { | |
1314 | #address-cells = <1>; | |
1315 | #size-cells = <1>; | |
1316 | #interrupt-cells = <2>; | |
1317 | device_type = "soc"; | |
1318 | ranges = <00000000 e0000000 00100000> | |
1319 | reg = <e0000000 00003000>; | |
1320 | ||
1321 | mdio@24520 { | |
1322 | reg = <24520 20>; | |
1323 | device_type = "mdio"; | |
1324 | compatible = "gianfar"; | |
1325 | ||
1326 | ethernet-phy@0 { | |
1327 | linux,phandle = <2452000> | |
1328 | interrupt-parent = <40000>; | |
1329 | interrupts = <35 1>; | |
1330 | reg = <0>; | |
1331 | device_type = "ethernet-phy"; | |
1332 | }; | |
1333 | ||
1334 | ethernet-phy@1 { | |
1335 | linux,phandle = <2452001> | |
1336 | interrupt-parent = <40000>; | |
1337 | interrupts = <35 1>; | |
1338 | reg = <1>; | |
1339 | device_type = "ethernet-phy"; | |
1340 | }; | |
1341 | ||
1342 | ethernet-phy@3 { | |
1343 | linux,phandle = <2452002> | |
1344 | interrupt-parent = <40000>; | |
1345 | interrupts = <35 1>; | |
1346 | reg = <3>; | |
1347 | device_type = "ethernet-phy"; | |
1348 | }; | |
1349 | ||
1350 | }; | |
1351 | ||
1352 | ethernet@24000 { | |
1353 | #size-cells = <0>; | |
1354 | device_type = "network"; | |
1355 | model = "TSEC"; | |
1356 | compatible = "gianfar"; | |
1357 | reg = <24000 1000>; | |
1358 | address = [ 00 E0 0C 00 73 00 ]; | |
1359 | interrupts = <d 3 e 3 12 3>; | |
1360 | interrupt-parent = <40000>; | |
1361 | phy-handle = <2452000>; | |
1362 | }; | |
1363 | ||
1364 | ethernet@25000 { | |
1365 | #address-cells = <1>; | |
1366 | #size-cells = <0>; | |
1367 | device_type = "network"; | |
1368 | model = "TSEC"; | |
1369 | compatible = "gianfar"; | |
1370 | reg = <25000 1000>; | |
1371 | address = [ 00 E0 0C 00 73 01 ]; | |
1372 | interrupts = <13 3 14 3 18 3>; | |
1373 | interrupt-parent = <40000>; | |
1374 | phy-handle = <2452001>; | |
1375 | }; | |
1376 | ||
1377 | ethernet@26000 { | |
1378 | #address-cells = <1>; | |
1379 | #size-cells = <0>; | |
1380 | device_type = "network"; | |
1381 | model = "FEC"; | |
1382 | compatible = "gianfar"; | |
1383 | reg = <26000 1000>; | |
1384 | address = [ 00 E0 0C 00 73 02 ]; | |
1385 | interrupts = <19 3>; | |
1386 | interrupt-parent = <40000>; | |
1387 | phy-handle = <2452002>; | |
1388 | }; | |
1389 | ||
1390 | serial@4500 { | |
1391 | device_type = "serial"; | |
1392 | compatible = "ns16550"; | |
1393 | reg = <4500 100>; | |
1394 | clock-frequency = <0>; | |
1395 | interrupts = <1a 3>; | |
1396 | interrupt-parent = <40000>; | |
1397 | }; | |
1398 | ||
1399 | pic@40000 { | |
1400 | linux,phandle = <40000>; | |
1401 | clock-frequency = <0>; | |
1402 | interrupt-controller; | |
1403 | #address-cells = <0>; | |
1404 | reg = <40000 40000>; | |
1405 | built-in; | |
1406 | compatible = "chrp,open-pic"; | |
1407 | device_type = "open-pic"; | |
1408 | big-endian; | |
1409 | }; | |
1410 | ||
1411 | i2c@3000 { | |
1412 | interrupt-parent = <40000>; | |
1413 | interrupts = <1b 3>; | |
1414 | reg = <3000 18>; | |
1415 | device_type = "i2c"; | |
1416 | compatible = "fsl-i2c"; | |
1417 | dfsrr; | |
1418 | }; | |
1419 | ||
1420 | }; |