summaryrefslogtreecommitdiff
path: root/Documentation/powerpc/booting-without-of.txt
blob: c169299716b1bb148aa3d3c537bc1ea4cf637a51 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
           Booting the Linux/ppc kernel without Open Firmware
           --------------------------------------------------

(c) 2005 Benjamin Herrenschmidt <benh at kernel.crashing.org>,
    IBM Corp.
(c) 2005 Becky Bruce <becky.bruce at freescale.com>,
    Freescale Semiconductor, FSL SOC and 32-bit additions
(c) 2006 MontaVista Software, Inc.
    Flash chip node definition

Table of Contents
=================

  I - Introduction
    1) Entry point for arch/powerpc
    2) Board support

  II - The DT block format
    1) Header
    2) Device tree generalities
    3) Device tree "structure" block
    4) Device tree "strings" block

  III - Required content of the device tree
    1) Note about cells and address representation
    2) Note about "compatible" properties
    3) Note about "name" properties
    4) Note about node and property names and character set
    5) Required nodes and properties
      a) The root node
      b) The /cpus node
      c) The /cpus/* nodes
      d) the /memory node(s)
      e) The /chosen node
      f) the /soc<SOCname> node

  IV - "dtc", the device tree compiler

  V - Recommendations for a bootloader

  VI - System-on-a-chip devices and nodes
    1) Defining child nodes of an SOC
    2) Representing devices without a current OF specification
      a) MDIO IO device
      c) PHY nodes
      b) Gianfar-compatible ethernet nodes
      d) Interrupt controllers
      e) I2C
      f) Freescale SOC USB controllers
      g) Freescale SOC SEC Security Engines
      h) Board Control and Status (BCSR)
      i) Freescale QUICC Engine module (QE)
      g) Flash chip nodes

  VII - Specifying interrupt information for devices
    1) interrupts property
    2) interrupt-parent property
    3) OpenPIC Interrupt Controllers
    4) ISA Interrupt Controllers

  Appendix A - Sample SOC node for MPC8540


Revision Information
====================

   May 18, 2005: Rev 0.1 - Initial draft, no chapter III yet.

   May 19, 2005: Rev 0.2 - Add chapter III and bits & pieces here or
                           clarifies the fact that a lot of things are
                           optional, the kernel only requires a very
                           small device tree, though it is encouraged
                           to provide an as complete one as possible.

   May 24, 2005: Rev 0.3 - Precise that DT block has to be in RAM
			 - Misc fixes
			 - Define version 3 and new format version 16
			   for the DT block (version 16 needs kernel
			   patches, will be fwd separately).
			   String block now has a size, and full path
			   is replaced by unit name for more
			   compactness.
			   linux,phandle is made optional, only nodes
			   that are referenced by other nodes need it.
			   "name" property is now automatically
			   deduced from the unit name

   June 1, 2005: Rev 0.4 - Correct confusion between OF_DT_END and
                           OF_DT_END_NODE in structure definition.
                         - Change version 16 format to always align
                           property data to 4 bytes. Since tokens are
                           already aligned, that means no specific
                           required alignment between property size
                           and property data. The old style variable
                           alignment would make it impossible to do
                           "simple" insertion of properties using
                           memmove (thanks Milton for
                           noticing). Updated kernel patch as well
			 - Correct a few more alignment constraints
			 - Add a chapter about the device-tree
                           compiler and the textural representation of
                           the tree that can be "compiled" by dtc.

   November 21, 2005: Rev 0.5
			 - Additions/generalizations for 32-bit
			 - Changed to reflect the new arch/powerpc
			   structure
			 - Added chapter VI


 ToDo:
	- Add some definitions of interrupt tree (simple/complex)
	- Add some definitions for PCI host bridges
	- Add some common address format examples
	- Add definitions for standard properties and "compatible"
	  names for cells that are not already defined by the existing
	  OF spec.
	- Compare FSL SOC use of PCI to standard and make sure no new
	  node definition required.
	- Add more information about node definitions for SOC devices
  	  that currently have no standard, like the FSL CPM.


I - Introduction
================

During the recent development of the Linux/ppc64 kernel, and more
specifically, the addition of new platform types outside of the old
IBM pSeries/iSeries pair, it was decided to enforce some strict rules
regarding the kernel entry and bootloader <-> kernel interfaces, in
order to avoid the degeneration that had become the ppc32 kernel entry
point and the way a new platform should be added to the kernel. The
legacy iSeries platform breaks those rules as it predates this scheme,
but no new board support will be accepted in the main tree that
doesn't follows them properly.  In addition, since the advent of the
arch/powerpc merged architecture for ppc32 and ppc64, new 32-bit
platforms and 32-bit platforms which move into arch/powerpc will be
required to use these rules as well.

The main requirement that will be defined in more detail below is
the presence of a device-tree whose format is defined after Open
Firmware specification. However, in order to make life easier
to embedded board vendors, the kernel doesn't require the device-tree
to represent every device in the system and only requires some nodes
and properties to be present. This will be described in detail in
section III, but, for example, the kernel does not require you to
create a node for every PCI device in the system. It is a requirement
to have a node for PCI host bridges in order to provide interrupt
routing informations and memory/IO ranges, among others. It is also
recommended to define nodes for on chip devices and other busses that
don't specifically fit in an existing OF specification. This creates a
great flexibility in the way the kernel can then probe those and match
drivers to device, without having to hard code all sorts of tables. It
also makes it more flexible for board vendors to do minor hardware
upgrades without significantly impacting the kernel code or cluttering
it with special cases.


1) Entry point for arch/powerpc
-------------------------------

   There is one and one single entry point to the kernel, at the start
   of the kernel image. That entry point supports two calling
   conventions:

        a) Boot from Open Firmware. If your firmware is compatible
        with Open Firmware (IEEE 1275) or provides an OF compatible
        client interface API (support for "interpret" callback of
        forth words isn't required), you can enter the kernel with:

              r5 : OF callback pointer as defined by IEEE 1275
              bindings to powerpc. Only the 32-bit client interface
              is currently supported

              r3, r4 : address & length of an initrd if any or 0

              The MMU is either on or off; the kernel will run the
              trampoline located in arch/powerpc/kernel/prom_init.c to
              extract the device-tree and other information from open
              firmware and build a flattened device-tree as described
              in b). prom_init() will then re-enter the kernel using
              the second method. This trampoline code runs in the
              context of the firmware, which is supposed to handle all
              exceptions during that time.

        b) Direct entry with a flattened device-tree block. This entry
        point is called by a) after the OF trampoline and can also be
        called directly by a bootloader that does not support the Open
        Firmware client interface. It is also used by "kexec" to
        implement "hot" booting of a new kernel from a previous
        running one. This method is what I will describe in more
        details in this document, as method a) is simply standard Open
        Firmware, and thus should be implemented according to the
        various standard documents defining it and its binding to the
        PowerPC platform. The entry point definition then becomes:

                r3 : physical pointer to the device-tree block
                (defined in chapter II) in RAM

                r4 : physical pointer to the kernel itself. This is
                used by the assembly code to properly disable the MMU
                in case you are entering the kernel with MMU enabled
                and a non-1:1 mapping.

                r5 : NULL (as to differentiate with method a)

        Note about SMP entry: Either your firmware puts your other
        CPUs in some sleep loop or spin loop in ROM where you can get
        them out via a soft reset or some other means, in which case
        you don't need to care, or you'll have to enter the kernel
        with all CPUs. The way to do that with method b) will be
        described in a later revision of this document.


2) Board support
----------------

64-bit kernels:

   Board supports (platforms) are not exclusive config options. An
   arbitrary set of board supports can be built in a single kernel
   image. The kernel will "know" what set of functions to use for a
   given platform based on the content of the device-tree. Thus, you
   should:

        a) add your platform support as a _boolean_ option in
        arch/powerpc/Kconfig, following the example of PPC_PSERIES,
        PPC_PMAC and PPC_MAPLE. The later is probably a good
        example of a board support to start from.

        b) create your main platform file as
        "arch/powerpc/platforms/myplatform/myboard_setup.c" and add it
        to the Makefile under the condition of your CONFIG_
        option. This file will define a structure of type "ppc_md"
        containing the various callbacks that the generic code will
        use to get to your platform specific code

        c) Add a reference to your "ppc_md" structure in the
        "machines" table in arch/powerpc/kernel/setup_64.c if you are
        a 64-bit platform.

        d) request and get assigned a platform number (see PLATFORM_*
        constants in include/asm-powerpc/processor.h

32-bit embedded kernels:

  Currently, board support is essentially an exclusive config option.
  The kernel is configured for a single platform.  Part of the reason
  for this is to keep kernels on embedded systems small and efficient;
  part of this is due to the fact the code is already that way. In the
  future, a kernel may support multiple platforms, but only if the
  platforms feature the same core architecture.  A single kernel build
  cannot support both configurations with Book E and configurations
  with classic Powerpc architectures.

  32-bit embedded platforms that are moved into arch/powerpc using a
  flattened device tree should adopt the merged tree practice of
  setting ppc_md up dynamically, even though the kernel is currently
  built with support for only a single platform at a time.  This allows
  unification of the setup code, and will make it easier to go to a
  multiple-platform-support model in the future.

NOTE: I believe the above will be true once Ben's done with the merge
of the boot sequences.... someone speak up if this is wrong!

  To add a 32-bit embedded platform support, follow the instructions
  for 64-bit platforms above, with the exception that the Kconfig
  option should be set up such that the kernel builds exclusively for
  the platform selected.  The processor type for the platform should
  enable another config option to select the specific board
  supported.

NOTE: If Ben doesn't merge the setup files, may need to change this to
point to setup_32.c


   I will describe later the boot process and various callbacks that
   your platform should implement.


II - The DT block format
========================


This chapter defines the actual format of the flattened device-tree
passed to the kernel. The actual content of it and kernel requirements
are described later. You can find example of code manipulating that
format in various places, including arch/powerpc/kernel/prom_init.c
which will generate a flattened device-tree from the Open Firmware
representation, or the fs2dt utility which is part of the kexec tools
which will generate one from a filesystem representation. It is
expected that a bootloader like uboot provides a bit more support,
that will be discussed later as well.

Note: The block has to be in main memory. It has to be accessible in
both real mode and virtual mode with no mapping other than main
memory. If you are writing a simple flash bootloader, it should copy
the block to RAM before passing it to the kernel.


1) Header
---------

   The kernel is entered with r3 pointing to an area of memory that is
   roughly described in include/asm-powerpc/prom.h by the structure
   boot_param_header:

struct boot_param_header {
        u32     magic;                  /* magic word OF_DT_HEADER */
        u32     totalsize;              /* total size of DT block */
        u32     off_dt_struct;          /* offset to structure */
        u32     off_dt_strings;         /* offset to strings */
        u32     off_mem_rsvmap;         /* offset to memory reserve map
                                           */
        u32     version;                /* format version */
        u32     last_comp_version;      /* last compatible version */

        /* version 2 fields below */
        u32     boot_cpuid_phys;        /* Which physical CPU id we're
                                           booting on */
        /* version 3 fields below */
        u32     size_dt_strings;        /* size of the strings block */

        /* version 17 fields below */
        u32	size_dt_struct;		/* size of the DT structure block */
};

   Along with the constants:

/* Definitions used by the flattened device tree */
#define OF_DT_HEADER            0xd00dfeed      /* 4: version,
						   4: total size */
#define OF_DT_BEGIN_NODE        0x1             /* Start node: full name
						   */
#define OF_DT_END_NODE          0x2             /* End node */
#define OF_DT_PROP              0x3             /* Property: name off,
                                                   size, content */
#define OF_DT_END               0x9

   All values in this header are in big endian format, the various
   fields in this header are defined more precisely below. All
   "offset" values are in bytes from the start of the header; that is
   from the value of r3.

   - magic

     This is a magic value that "marks" the beginning of the
     device-tree block header. It contains the value 0xd00dfeed and is
     defined by the constant OF_DT_HEADER

   - totalsize

     This is the total size of the DT block including the header. The
     "DT" block should enclose all data structures defined in this
     chapter (who are pointed to by offsets in this header). That is,
     the device-tree structure, strings, and the memory reserve map.

   - off_dt_struct

     This is an offset from the beginning of the header to the start
     of the "structure" part the device tree. (see 2) device tree)

   - off_dt_strings

     This is an offset from the beginning of the header to the start
     of the "strings" part of the device-tree

   - off_mem_rsvmap

     This is an offset from the beginning of the header to the start
     of the reserved memory map. This map is a list of pairs of 64-
     bit integers. Each pair is a physical address and a size. The
     list is terminated by an entry of size 0. This map provides the
     kernel with a list of physical memory areas that are "reserved"
     and thus not to be used for memory allocations, especially during
     early initialization. The kernel needs to allocate memory during
     boot for things like un-flattening the device-tree, allocating an
     MMU hash table, etc... Those allocations must be done in such a
     way to avoid overriding critical things like, on Open Firmware
     capable machines, the RTAS instance, or on some pSeries, the TCE
     tables used for the iommu. Typically, the reserve map should
     contain _at least_ this DT block itself (header,total_size). If
     you are passing an initrd to the kernel, you should reserve it as
     well. You do not need to reserve the kernel image itself. The map
     should be 64-bit aligned.

   - version

     This is the version of this structure. Version 1 stops
     here. Version 2 adds an additional field boot_cpuid_phys.
     Version 3 adds the size of the strings block, allowing the kernel
     to reallocate it easily at boot and free up the unused flattened
     structure after expansion. Version 16 introduces a new more
     "compact" format for the tree itself that is however not backward
     compatible. Version 17 adds an additional field, size_dt_struct,
     allowing it to be reallocated or moved more easily (this is
     particularly useful for bootloaders which need to make
     adjustments to a device tree based on probed information). You
     should always generate a structure of the highest version defined
     at the time of your implementation. Currently that is version 17,
     unless you explicitly aim at being backward compatible.

   - last_comp_version

     Last compatible version. This indicates down to what version of
     the DT block you are backward compatible. For example, version 2
     is backward compatible with version 1 (that is, a kernel build
     for version 1 will be able to boot with a version 2 format). You
     should put a 1 in this field if you generate a device tree of
     version 1 to 3, or 16 if you generate a tree of version 16 or 17
     using the new unit name format.

   - boot_cpuid_phys

     This field only exist on version 2 headers. It indicate which
     physical CPU ID is calling the kernel entry point. This is used,
     among others, by kexec. If you are on an SMP system, this value
     should match the content of the "reg" property of the CPU node in
     the device-tree corresponding to the CPU calling the kernel entry
     point (see further chapters for more informations on the required
     device-tree contents)

   - size_dt_strings

     This field only exists on version 3 and later headers.  It
     gives the size of the "strings" section of the device tree (which
     starts at the offset given by off_dt_strings).

   - size_dt_struct

     This field only exists on version 17 and later headers.  It gives
     the size of the "structure" section of the device tree (which
     starts at the offset given by off_dt_struct).

   So the typical layout of a DT block (though the various parts don't
   need to be in that order) looks like this (addresses go from top to
   bottom):


             ------------------------------
       r3 -> |  struct boot_param_header  |
             ------------------------------
             |      (alignment gap) (*)   |
             ------------------------------
             |      memory reserve map    |
             ------------------------------
             |      (alignment gap)       |
             ------------------------------
             |                            |
             |    device-tree structure   |
             |                            |
             ------------------------------
             |      (alignment gap)       |
             ------------------------------
             |                            |
             |     device-tree strings    |
             |                            |
      -----> ------------------------------
      |
      |
      --- (r3 + totalsize)

  (*) The alignment gaps are not necessarily present; their presence
      and size are dependent on the various alignment requirements of
      the individual data blocks.


2) Device tree generalities
---------------------------

This device-tree itself is separated in two different blocks, a
structure block and a strings block. Both need to be aligned to a 4
byte boundary.

First, let's quickly describe the device-tree concept before detailing
the storage format. This chapter does _not_ describe the detail of the
required types of nodes & properties for the kernel, this is done
later in chapter III.

The device-tree layout is strongly inherited from the definition of
the Open Firmware IEEE 1275 device-tree. It's basically a tree of
nodes, each node having two or more named properties. A property can
have a value or not.

It is a tree, so each node has one and only one parent except for the
root node who has no parent.

A node has 2 names. The actual node name is generally contained in a
property of type "name" in the node property list whose value is a
zero terminated string and is mandatory for version 1 to 3 of the
format definition (as it is in Open Firmware). Version 16 makes it
optional as it can generate it from the unit name defined below.

There is also a "unit name" that is used to differentiate nodes with
the same name at the same level, it is usually made of the node
names, the "@" sign, and a "unit address", which definition is
specific to the bus type the node sits on.

The unit name doesn't exist as a property per-se but is included in
the device-tree structure. It is typically used to represent "path" in
the device-tree. More details about the actual format of these will be
below.

The kernel powerpc generic code does not make any formal use of the
unit address (though some board support code may do) so the only real
requirement here for the unit address is to ensure uniqueness of
the node unit name at a given level of the tree. Nodes with no notion
of address and no possible sibling of the same name (like /memory or
/cpus) may omit the unit address in the context of this specification,
or use the "@0" default unit address. The unit name is used to define
a node "full path", which is the concatenation of all parent node
unit names separated with "/".

The root node doesn't have a defined name, and isn't required to have
a name property either if you are using version 3 or earlier of the
format. It also has no unit address (no @ symbol followed by a unit
address). The root node unit name is thus an empty string. The full
path to the root node is "/".

Every node which actually represents an actual device (that is, a node
which isn't only a virtual "container" for more nodes, like "/cpus"
is) is also required to have a "device_type" property indicating the
type of node .

Finally, every node that can be referenced from a property in another
node is required to have a "linux,phandle" property. Real open
firmware implementations provide a unique "phandle" value for every
node that the "prom_init()" trampoline code turns into
"linux,phandle" properties. However, this is made optional if the
flattened device tree is used directly. An example of a node
referencing another node via "phandle" is when laying out the
interrupt tree which will be described in a further version of this
document.

This "linux, phandle" property is a 32-bit value that uniquely
identifies a node. You are free to use whatever values or system of
values, internal pointers, or whatever to generate these, the only
requirement is that every node for which you provide that property has
a unique value for it.

Here is an example of a simple device-tree. In this example, an "o"
designates a node followed by the node unit name. Properties are
presented with their name followed by their content. "content"
represents an ASCII string (zero terminated) value, while <content>
represents a 32-bit hexadecimal value. The various nodes in this
example will be discussed in a later chapter. At this point, it is
only meant to give you a idea of what a device-tree looks like. I have
purposefully kept the "name" and "linux,phandle" properties which
aren't necessary in order to give you a better idea of what the tree
looks like in practice.

  / o device-tree
      |- name = "device-tree"
      |- model = "MyBoardName"
      |- compatible = "MyBoardFamilyName"
      |- #address-cells = <2>
      |- #size-cells = <2>
      |- linux,phandle = <0>
      |
      o cpus
      | | - name = "cpus"
      | | - linux,phandle = <1>
      | | - #address-cells = <1>
      | | - #size-cells = <0>
      | |
      | o PowerPC,970@0
      |   |- name = "PowerPC,970"
      |   |- device_type = "cpu"
      |   |- reg = <0>
      |   |- clock-frequency = <5f5e1000>
      |   |- 64-bit
      |   |- linux,phandle = <2>
      |
      o memory@0
      | |- name = "memory"
      | |- device_type = "memory"
      | |- reg = <00000000 00000000 00000000 20000000>
      | |- linux,phandle = <3>
      |
      o chosen
        |- name = "chosen"
        |- bootargs = "root=/dev/sda2"
        |- linux,phandle = <4>

This tree is almost a minimal tree. It pretty much contains the
minimal set of required nodes and properties to boot a linux kernel;
that is, some basic model informations at the root, the CPUs, and the
physical memory layout.  It also includes misc information passed
through /chosen, like in this example, the platform type (mandatory)
and the kernel command line arguments (optional).

The /cpus/PowerPC,970@0/64-bit property is an example of a
property without a value. All other properties have a value. The
significance of the #address-cells and #size-cells properties will be
explained in chapter IV which defines precisely the required nodes and
properties and their content.


3) Device tree "structure" block

The structure of the device tree is a linearized tree structure. The
"OF_DT_BEGIN_NODE" token starts a new node, and the "OF_DT_END_NODE"
ends that node definition. Child nodes are simply defined before
"OF_DT_END_NODE" (that is nodes within the node). A 'token' is a 32
bit value. The tree has to be "finished" with a OF_DT_END token

Here's the basic structure of a single node:

     * token OF_DT_BEGIN_NODE (that is 0x00000001)
     * for version 1 to 3, this is the node full path as a zero
       terminated string, starting with "/". For version 16 and later,
       this is the node unit name only (or an empty string for the
       root node)
     * [align gap to next 4 bytes boundary]
     * for each property:
        * token OF_DT_PROP (that is 0x00000003)
        * 32-bit value of property value size in bytes (or 0 if no
          value)
        * 32-bit value of offset in string block of property name
        * property value data if any
        * [align gap to next 4 bytes boundary]
     * [child nodes if any]
     * token OF_DT_END_NODE (that is 0x00000002)

So the node content can be summarized as a start token, a full path,
a list of properties, a list of child nodes, and an end token. Every
child node is a full node structure itself as defined above.

NOTE: The above definition requires that all property definitions for
a particular node MUST precede any subnode definitions for that node.
Although the structure would not be ambiguous if properties and
subnodes were intermingled, the kernel parser requires that the
properties come first (up until at least 2.6.22).  Any tools
manipulating a flattened tree must take care to preserve this
constraint.

4) Device tree "strings" block

In order to save space, property names, which are generally redundant,
are stored separately in the "strings" block. This block is simply the
whole bunch of zero terminated strings for all property names
concatenated together. The device-tree property definitions in the
structure block will contain offset values from the beginning of the
strings block.


III - Required content of the device tree
=========================================

WARNING: All "linux,*" properties defined in this document apply only
to a flattened device-tree. If your platform uses a real
implementation of Open Firmware or an implementation compatible with
the Open Firmware client interface, those properties will be created
by the trampoline code in the kernel's prom_init() file. For example,
that's where you'll have to add code to detect your board model and
set the platform number. However, when using the flattened device-tree
entry point, there is no prom_init() pass, and thus you have to
provide those properties yourself.


1) Note about cells and address representation
----------------------------------------------

The general rule is documented in the various Open Firmware
documentations. If you choose to describe a bus with the device-tree
and there exist an OF bus binding, then you should follow the
specification. However, the kernel does not require every single
device or bus to be described by the device tree.

In general, the format of an address for a device is defined by the
parent bus type, based on the #address-cells and #size-cells
property. In the absence of such a property, the parent's parent
values are used, etc... The kernel requires the root node to have
those properties defining addresses format for devices directly mapped
on the processor bus.

Those 2 properties define 'cells' for representing an address and a
size. A "cell" is a 32-bit number. For example, if both contain 2
like the example tree given above, then an address and a size are both
composed of 2 cells, and each is a 64-bit number (cells are
concatenated and expected to be in big endian format). Another example
is the way Apple firmware defines them, with 2 cells for an address
and one cell for a size.  Most 32-bit implementations should define
#address-cells and #size-cells to 1, which represents a 32-bit value.
Some 32-bit processors allow for physical addresses greater than 32
bits; these processors should define #address-cells as 2.

"reg" properties are always a tuple of the type "address size" where
the number of cells of address and size is specified by the bus
#address-cells and #size-cells. When a bus supports various address
spaces and other flags relative to a given address allocation (like
prefetchable, etc...) those flags are usually added to the top level
bits of the physical address. For example, a PCI physical address is
made of 3 cells, the bottom two containing the actual address itself
while the top cell contains address space indication, flags, and pci
bus & device numbers.

For busses that support dynamic allocation, it's the accepted practice
to then not provide the address in "reg" (keep it 0) though while
providing a flag indicating the address is dynamically allocated, and
then, to provide a separate "assigned-addresses" property that
contains the fully allocated addresses. See the PCI OF bindings for
details.

In general, a simple bus with no address space bits and no dynamic
allocation is preferred if it reflects your hardware, as the existing
kernel address parsing functions will work out of the box. If you
define a bus type with a more complex address format, including things
like address space bits, you'll have to add a bus translator to the
prom_parse.c file of the recent kernels for your bus type.

The "reg" property only defines addresses and sizes (if #size-cells
is non-0) within a given bus. In order to translate addresses upward
(that is into parent bus addresses, and possibly into CPU physical
addresses), all busses must contain a "ranges" property. If the
"ranges" property is missing at a given level, it's assumed that
translation isn't possible. The format of the "ranges" property for a
bus is a list of:

	bus address, parent bus address, size

"bus address" is in the format of the bus this bus node is defining,
that is, for a PCI bridge, it would be a PCI address. Thus, (bus
address, size) defines a range of addresses for child devices. "parent
bus address" is in the format of the parent bus of this bus. For
example, for a PCI host controller, that would be a CPU address. For a
PCI<->ISA bridge, that would be a PCI address. It defines the base
address in the parent bus where the beginning of that range is mapped.

For a new 64-bit powerpc board, I recommend either the 2/2 format or
Apple's 2/1 format which is slightly more compact since sizes usually
fit in a single 32-bit word.   New 32-bit powerpc boards should use a
1/1 format, unless the processor supports physical addresses greater
than 32-bits, in which case a 2/1 format is recommended.


2) Note about "compatible" properties
-------------------------------------

These properties are optional, but recommended in devices and the root
node. The format of a "compatible" property is a list of concatenated
zero terminated strings. They allow a device to express its
compatibility with a family of similar devices, in some cases,
allowing a single driver to match against several devices regardless
of their actual names.

3) Note about "name" properties
-------------------------------

While earlier users of Open Firmware like OldWorld macintoshes tended
to use the actual device name for the "name" property, it's nowadays
considered a good practice to use a name that is closer to the device
class (often equal to device_type). For example, nowadays, ethernet
controllers are named "ethernet", an additional "model" property
defining precisely the chip type/model, and "compatible" property
defining the family in case a single driver can driver more than one
of these chips. However, the kernel doesn't generally put any
restriction on the "name" property; it is simply considered good
practice to follow the standard and its evolutions as closely as
possible.

Note also that the new format version 16 makes the "name" property
optional. If it's absent for a node, then the node's unit name is then
used to reconstruct the name. That is, the part of the unit name
before the "@" sign is used (or the entire unit name if no "@" sign
is present).

4) Note about node and property names and character set
-------------------------------------------------------

While open firmware provides more flexible usage of 8859-1, this
specification enforces more strict rules. Nodes and properties should
be comprised only of ASCII characters 'a' to 'z', '0' to
'9', ',', '.', '_', '+', '#', '?', and '-'. Node names additionally
allow uppercase characters 'A' to 'Z' (property names should be
lowercase. The fact that vendors like Apple don't respect this rule is
irrelevant here). Additionally, node and property names should always
begin with a character in the range 'a' to 'z' (or 'A' to 'Z' for node
names).

The maximum number of characters for both nodes and property names
is 31. In the case of node names, this is only the leftmost part of
a unit name (the pure "name" property), it doesn't include the unit
address which can extend beyond that limit.


5) Required nodes and properties
--------------------------------
  These are all that are currently required. However, it is strongly
  recommended that you expose PCI host bridges as documented in the
  PCI binding to open firmware, and your interrupt tree as documented
  in OF interrupt tree specification.

  a) The root node

  The root node requires some properties to be present:

    - model : this is your board name/model
    - #address-cells : address representation for "root" devices
    - #size-cells: the size representation for "root" devices
    - device_type : This property shouldn't be necessary. However, if
      you decide to create a device_type for your root node, make sure it
      is _not_ "chrp" unless your platform is a pSeries or PAPR compliant
      one for 64-bit, or a CHRP-type machine for 32-bit as this will
      matched by the kernel this way.

  Additionally, some recommended properties are:

    - compatible : the board "family" generally finds its way here,
      for example, if you have 2 board models with a similar layout,
      that typically get driven by the same platform code in the
      kernel, you would use a different "model" property but put a
      value in "compatible". The kernel doesn't directly use that
      value but it is generally useful.

  The root node is also generally where you add additional properties
  specific to your board like the serial number if any, that sort of
  thing. It is recommended that if you add any "custom" property whose
  name may clash with standard defined ones, you prefix them with your
  vendor name and a comma.

  b) The /cpus node

  This node is the parent of all individual CPU nodes. It doesn't
  have any specific requirements, though it's generally good practice
  to have at least:

               #address-cells = <00000001>
               #size-cells    = <00000000>

  This defines that the "address" for a CPU is a single cell, and has
  no meaningful size. This is not necessary but the kernel will assume
  that format when reading the "reg" properties of a CPU node, see
  below

  c) The /cpus/* nodes

  So under /cpus, you are supposed to create a node for every CPU on
  the machine. There is no specific restriction on the name of the
  CPU, though It's common practice to call it PowerPC,<name>. For
  example, Apple uses PowerPC,G5 while IBM uses PowerPC,970FX.

  Required properties:

    - device_type : has to be "cpu"
    - reg : This is the physical CPU number, it's a single 32-bit cell
      and is also used as-is as the unit number for constructing the
      unit name in the full path. For example, with 2 CPUs, you would
      have the full path:
        /cpus/PowerPC,970FX@0
        /cpus/PowerPC,970FX@1
      (unit addresses do not require leading zeroes)
    - d-cache-line-size : one cell, L1 data cache line size in bytes
    - i-cache-line-size : one cell, L1 instruction cache line size in
      bytes
    - d-cache-size : one cell, size of L1 data cache in bytes
    - i-cache-size : one cell, size of L1 instruction cache in bytes

  Recommended properties:

    - timebase-frequency : a cell indicating the frequency of the
      timebase in Hz. This is not directly used by the generic code,
      but you are welcome to copy/paste the pSeries code for setting
      the kernel timebase/decrementer calibration based on this
      value.
    - clock-frequency : a cell indicating the CPU core clock frequency
      in Hz. A new property will be defined for 64-bit values, but if
      your frequency is < 4Ghz, one cell is enough. Here as well as
      for the above, the common code doesn't use that property, but
      you are welcome to re-use the pSeries or Maple one. A future
      kernel version might provide a common function for this.

  You are welcome to add any property you find relevant to your board,
  like some information about the mechanism used to soft-reset the
  CPUs. For example, Apple puts the GPIO number for CPU soft reset
  lines in there as a "soft-reset" property since they start secondary
  CPUs by soft-resetting them.


  d) the /memory node(s)

  To define the physical memory layout of your board, you should
  create one or more memory node(s). You can either create a single
  node with all memory ranges in its reg property, or you can create
  several nodes, as you wish. The unit address (@ part) used for the
  full path is the address of the first range of memory defined by a
  given node. If you use a single memory node, this will typically be
  @0.

  Required properties:

    - device_type : has to be "memory"
    - reg : This property contains all the physical memory ranges of
      your board. It's a list of addresses/sizes concatenated
      together, with the number of cells of each defined by the
      #address-cells and #size-cells of the root node. For example,
      with both of these properties being 2 like in the example given
      earlier, a 970 based machine with 6Gb of RAM could typically
      have a "reg" property here that looks like:

      00000000 00000000 00000000 80000000
      00000001 00000000 00000001 00000000

      That is a range starting at 0 of 0x80000000 bytes and a range
      starting at 0x100000000 and of 0x100000000 bytes. You can see
      that there is no memory covering the IO hole between 2Gb and
      4Gb. Some vendors prefer splitting those ranges into smaller
      segments, but the kernel doesn't care.

  e) The /chosen node

  This node is a bit "special". Normally, that's where open firmware
  puts some variable environment information, like the arguments, or
  the default input/output devices.

  This specification makes a few of these mandatory, but also defines
  some linux-specific properties that would be normally constructed by
  the prom_init() trampoline when booting with an OF client interface,
  but that you have to provide yourself when using the flattened format.

  Recommended properties:

    - bootargs : This zero-terminated string is passed as the kernel
      command line
    - linux,stdout-path : This is the full path to your standard
      console device if any. Typically, if you have serial devices on
      your board, you may want to put the full path to the one set as
      the default console in the firmware here, for the kernel to pick
      it up as its own default console. If you look at the function
      set_preferred_console() in arch/ppc64/kernel/setup.c, you'll see
      that the kernel tries to find out the default console and has
      knowledge of various types like 8250 serial ports. You may want
      to extend this function to add your own.

  Note that u-boot creates and fills in the chosen node for platforms
  that use it.

  (Note: a practice that is now obsolete was to include a property
  under /chosen called interrupt-controller which had a phandle value
  that pointed to the main interrupt controller)

  f) the /soc<SOCname> node

  This node is used to represent a system-on-a-chip (SOC) and must be
  present if the processor is a SOC. The top-level soc node contains
  information that is global to all devices on the SOC. The node name
  should contain a unit address for the SOC, which is the base address
  of the memory-mapped register set for the SOC. The name of an soc
  node should start with "soc", and the remainder of the name should
  represent the part number for the soc.  For example, the MPC8540's
  soc node would be called "soc8540".

  Required properties:

    - device_type : Should be "soc"
    - ranges : Should be defined as specified in 1) to describe the
      translation of SOC addresses for memory mapped SOC registers.
    - bus-frequency: Contains the bus frequency for the SOC node.
      Typically, the value of this field is filled in by the boot
      loader. 


  Recommended properties:

    - reg : This property defines the address and size of the
      memory-mapped registers that are used for the SOC node itself.
      It does not include the child device registers - these will be
      defined inside each child node.  The address specified in the
      "reg" property should match the unit address of the SOC node.
    - #address-cells : Address representation for "soc" devices.  The
      format of this field may vary depending on whether or not the
      device registers are memory mapped.  For memory mapped
      registers, this field represents the number of cells needed to
      represent the address of the registers.  For SOCs that do not
      use MMIO, a special address format should be defined that
      contains enough cells to represent the required information.
      See 1) above for more details on defining #address-cells.
    - #size-cells : Size representation for "soc" devices
    - #interrupt-cells : Defines the width of cells used to represent
       interrupts.  Typically this value is <2>, which includes a
       32-bit number that represents the interrupt number, and a
       32-bit number that represents the interrupt sense and level.
       This field is only needed if the SOC contains an interrupt
       controller.

  The SOC node may contain child nodes for each SOC device that the
  platform uses.  Nodes should not be created for devices which exist
  on the SOC but are not used by a particular platform. See chapter VI
  for more information on how to specify devices that are part of a SOC.

  Example SOC node for the MPC8540:

	soc8540@e0000000 {
		#address-cells = <1>;
		#size-cells = <1>;
		#interrupt-cells = <2>;
		device_type = "soc";
		ranges = <00000000 e0000000 00100000>
		reg = <e0000000 00003000>;
		bus-frequency = <0>;
	}



IV - "dtc", the device tree compiler
====================================


dtc source code can be found at
<http://ozlabs.org/~dgibson/dtc/dtc.tar.gz>

WARNING: This version is still in early development stage; the
resulting device-tree "blobs" have not yet been validated with the
kernel. The current generated bloc lacks a useful reserve map (it will
be fixed to generate an empty one, it's up to the bootloader to fill
it up) among others. The error handling needs work, bugs are lurking,
etc...

dtc basically takes a device-tree in a given format and outputs a
device-tree in another format. The currently supported formats are:

  Input formats:
  -------------

     - "dtb": "blob" format, that is a flattened device-tree block
       with
        header all in a binary blob.
     - "dts": "source" format. This is a text file containing a
       "source" for a device-tree. The format is defined later in this
        chapter.
     - "fs" format. This is a representation equivalent to the
        output of /proc/device-tree, that is nodes are directories and
	properties are files

 Output formats:
 ---------------

     - "dtb": "blob" format
     - "dts": "source" format
     - "asm": assembly language file. This is a file that can be
       sourced by gas to generate a device-tree "blob". That file can
       then simply be added to your Makefile. Additionally, the
       assembly file exports some symbols that can be used.


The syntax of the dtc tool is

    dtc [-I <input-format>] [-O <output-format>]
        [-o output-filename] [-V output_version] input_filename


The "output_version" defines what version of the "blob" format will be
generated. Supported versions are 1,2,3 and 16. The default is
currently version 3 but that may change in the future to version 16.

Additionally, dtc performs various sanity checks on the tree, like the
uniqueness of linux, phandle properties, validity of strings, etc...

The format of the .dts "source" file is "C" like, supports C and C++
style comments.

/ {
}

The above is the "device-tree" definition. It's the only statement
supported currently at the toplevel.

/ {
  property1 = "string_value";	/* define a property containing a 0
                                 * terminated string
				 */

  property2 = <1234abcd>;	/* define a property containing a
                                 * numerical 32-bit value (hexadecimal)
				 */

  property3 = <12345678 12345678 deadbeef>;
                                /* define a property containing 3
                                 * numerical 32-bit values (cells) in
                                 * hexadecimal
				 */
  property4 = [0a 0b 0c 0d de ea ad be ef];
                                /* define a property whose content is
                                 * an arbitrary array of bytes
                                 */

  childnode@addresss {	/* define a child node named "childnode"
                                 * whose unit name is "childnode at
				 * address"
                                 */

    childprop = "hello\n";      /* define a property "childprop" of
                                 * childnode (in this case, a string)
                                 */
  };
};

Nodes can contain other nodes etc... thus defining the hierarchical
structure of the tree.

Strings support common escape sequences from C: "\n", "\t", "\r",
"\(octal value)", "\x(hex value)".

It is also suggested that you pipe your source file through cpp (gcc
preprocessor) so you can use #include's, #define for constants, etc...

Finally, various options are planned but not yet implemented, like
automatic generation of phandles, labels (exported to the asm file so
you can point to a property content and change it easily from whatever
you link the device-tree with), label or path instead of numeric value
in some cells to "point" to a node (replaced by a phandle at compile
time), export of reserve map address to the asm file, ability to
specify reserve map content at compile time, etc...

We may provide a .h include file with common definitions of that
proves useful for some properties (like building PCI properties or
interrupt maps) though it may be better to add a notion of struct
definitions to the compiler...


V - Recommendations for a bootloader
====================================


Here are some various ideas/recommendations that have been proposed
while all this has been defined and implemented.

  - The bootloader may want to be able to use the device-tree itself
    and may want to manipulate it (to add/edit some properties,
    like physical memory size or kernel arguments). At this point, 2
    choices can be made. Either the bootloader works directly on the
    flattened format, or the bootloader has its own internal tree
    representation with pointers (similar to the kernel one) and
    re-flattens the tree when booting the kernel. The former is a bit
    more difficult to edit/modify, the later requires probably a bit
    more code to handle the tree structure. Note that the structure
    format has been designed so it's relatively easy to "insert"
    properties or nodes or delete them by just memmoving things
    around. It contains no internal offsets or pointers for this
    purpose.

  - An example of code for iterating nodes & retrieving properties
    directly from the flattened tree format can be found in the kernel
    file arch/ppc64/kernel/prom.c, look at scan_flat_dt() function,
    its usage in early_init_devtree(), and the corresponding various
    early_init_dt_scan_*() callbacks. That code can be re-used in a
    GPL bootloader, and as the author of that code, I would be happy
    to discuss possible free licensing to any vendor who wishes to
    integrate all or part of this code into a non-GPL bootloader.



VI - System-on-a-chip devices and nodes
=======================================

Many companies are now starting to develop system-on-a-chip
processors, where the processor core (CPU) and many peripheral devices
exist on a single piece of silicon.  For these SOCs, an SOC node
should be used that defines child nodes for the devices that make
up the SOC. While platforms are not required to use this model in
order to boot the kernel, it is highly encouraged that all SOC
implementations define as complete a flat-device-tree as possible to
describe the devices on the SOC.  This will allow for the
genericization of much of the kernel code.


1) Defining child nodes of an SOC
---------------------------------

Each device that is part of an SOC may have its own node entry inside
the SOC node.  For each device that is included in the SOC, the unit
address property represents the address offset for this device's
memory-mapped registers in the parent's address space.  The parent's
address space is defined by the "ranges" property in the top-level soc
node. The "reg" property for each node that exists directly under the
SOC node should contain the address mapping from the child address space
to the parent SOC address space and the size of the device's
memory-mapped register file.

For many devices that may exist inside an SOC, there are predefined
specifications for the format of the device tree node.  All SOC child
nodes should follow these specifications, except where noted in this
document.

See appendix A for an example partial SOC node definition for the
MPC8540.


2) Representing devices without a current OF specification
----------------------------------------------------------

Currently, there are many devices on SOCs that do not have a standard
representation pre-defined as part of the open firmware
specifications, mainly because the boards that contain these SOCs are
not currently booted using open firmware.   This section contains
descriptions for the SOC devices for which new nodes have been
defined; this list will expand as more and more SOC-containing
platforms are moved over to use the flattened-device-tree model.

  a) MDIO IO device

  The MDIO is a bus to which the PHY devices are connected.  For each
  device that exists on this bus, a child node should be created.  See
  the definition of the PHY node below for an example of how to define
  a PHY.

  Required properties:
    - reg : Offset and length of the register set for the device
    - device_type : Should be "mdio"
    - compatible : Should define the compatible device type for the
      mdio.  Currently, this is most likely to be "gianfar"

  Example:

	mdio@24520 {
		reg = <24520 20>;
		device_type = "mdio"; 
		compatible = "gianfar";

		ethernet-phy@0 {
			......
		};
	};


  b) Gianfar-compatible ethernet nodes

  Required properties:

    - device_type : Should be "network"
    - model : Model of the device.  Can be "TSEC", "eTSEC", or "FEC"
    - compatible : Should be "gianfar"
    - reg : Offset and length of the register set for the device
    - mac-address : List of bytes representing the ethernet address of
      this controller
    - interrupts : <a b> where a is the interrupt number and b is a
      field that represents an encoding of the sense and level
      information for the interrupt.  This should be encoded based on
      the information in section 2) depending on the type of interrupt
      controller you have.
    - interrupt-parent : the phandle for the interrupt controller that
      services interrupts for this device.
    - phy-handle : The phandle for the PHY connected to this ethernet
      controller.

  Recommended properties:

    - linux,network-index : This is the intended "index" of this
      network device.  This is used by the bootwrapper to interpret
      MAC addresses passed by the firmware when no information other
      than indices is available to associate an address with a device.

  Example:

	ethernet@24000 {
		#size-cells = <0>;
		device_type = "network";
		model = "TSEC";
		compatible = "gianfar";
		reg = <24000 1000>;
		mac-address = [ 00 E0 0C 00 73 00 ];
		interrupts = <d 3 e 3 12 3>;
		interrupt-parent = <40000>;
		phy-handle = <2452000>
	};



   c) PHY nodes

   Required properties:

    - device_type : Should be "ethernet-phy"
    - interrupts : <a b> where a is the interrupt number and b is a
      field that represents an encoding of the sense and level
      information for the interrupt.  This should be encoded based on
      the information in section 2) depending on the type of interrupt
      controller you have.
    - interrupt-parent : the phandle for the interrupt controller that
      services interrupts for this device.
    - reg : The ID number for the phy, usually a small integer
    - linux,phandle :  phandle for this node; likely referenced by an
      ethernet controller node.


   Example:

	ethernet-phy@0 {
		linux,phandle = <2452000>
		interrupt-parent = <40000>;
		interrupts = <35 1>;
		reg = <0>;
		device_type = "ethernet-phy";
	};


   d) Interrupt controllers

   Some SOC devices contain interrupt controllers that are different
   from the standard Open PIC specification.  The SOC device nodes for
   these types of controllers should be specified just like a standard
   OpenPIC controller.  Sense and level information should be encoded
   as specified in section 2) of this chapter for each device that
   specifies an interrupt.

   Example :

	pic@40000 {
		linux,phandle = <40000>;
		clock-frequency = <0>;
		interrupt-controller;
		#address-cells = <0>;
		reg = <40000 40000>;
		built-in;
		compatible = "chrp,open-pic";
		device_type = "open-pic";
		big-endian;
	};


   e) I2C

   Required properties :

    - device_type : Should be "i2c"
    - reg : Offset and length of the register set for the device

   Recommended properties :

    - compatible : Should be "fsl-i2c" for parts compatible with
      Freescale I2C specifications.
    - interrupts : <a b> where a is the interrupt number and b is a
      field that represents an encoding of the sense and level
      information for the interrupt.  This should be encoded based on
      the information in section 2) depending on the type of interrupt
      controller you have.
    - interrupt-parent : the phandle for the interrupt controller that
      services interrupts for this device.
    - dfsrr : boolean; if defined, indicates that this I2C device has
      a digital filter sampling rate register
    - fsl5200-clocking : boolean; if defined, indicated that this device
      uses the FSL 5200 clocking mechanism.

   Example :

	i2c@3000 {
		interrupt-parent = <40000>;
		interrupts = <1b 3>;
		reg = <3000 18>;
		device_type = "i2c";
		compatible  = "fsl-i2c";
		dfsrr;
	};


   f) Freescale SOC USB controllers

   The device node for a USB controller that is part of a Freescale
   SOC is as described in the document "Open Firmware Recommended
   Practice : Universal Serial Bus" with the following modifications
   and additions :  

   Required properties :
    - compatible : Should be "fsl-usb2-mph" for multi port host USB
      controllers, or "fsl-usb2-dr" for dual role USB controllers
    - phy_type : For multi port host USB controllers, should be one of
      "ulpi", or "serial". For dual role USB controllers, should be
      one of "ulpi", "utmi", "utmi_wide", or "serial".
    - reg : Offset and length of the register set for the device
    - port0 : boolean; if defined, indicates port0 is connected for
      fsl-usb2-mph compatible controllers.  Either this property or
      "port1" (or both) must be defined for "fsl-usb2-mph" compatible 
      controllers.
    - port1 : boolean; if defined, indicates port1 is connected for
      fsl-usb2-mph compatible controllers.  Either this property or
      "port0" (or both) must be defined for "fsl-usb2-mph" compatible 
      controllers.
    - dr_mode : indicates the working mode for "fsl-usb2-dr" compatible
      controllers.  Can be "host", "peripheral", or "otg".  Default to
      "host" if not defined for backward compatibility.

   Recommended properties :
    - interrupts : <a b> where a is the interrupt number and b is a
      field that represents an encoding of the sense and level
      information for the interrupt.  This should be encoded based on
      the information in section 2) depending on the type of interrupt
      controller you have.
    - interrupt-parent : the phandle for the interrupt controller that
      services interrupts for this device.

   Example multi port host USB controller device node :
	usb@22000 {
	        device_type = "usb";
		compatible = "fsl-usb2-mph";
		reg = <22000 1000>;
		#address-cells = <1>;
		#size-cells = <0>;
		interrupt-parent = <700>;
		interrupts = <27 1>;
		phy_type = "ulpi";
		port0;
		port1;
	};

   Example dual role USB controller device node :
	usb@23000 {
		device_type = "usb";
		compatible = "fsl-usb2-dr";
		reg = <23000 1000>;
		#address-cells = <1>;
		#size-cells = <0>;
		interrupt-parent = <700>;
		interrupts = <26 1>;
		dr_mode = "otg";
		phy = "ulpi";
	};


   g) Freescale SOC SEC Security Engines

   Required properties:

    - device_type : Should be "crypto"
    - model : Model of the device.  Should be "SEC1" or "SEC2"
    - compatible : Should be "talitos"
    - reg : Offset and length of the register set for the device
    - interrupts : <a b> where a is the interrupt number and b is a
      field that represents an encoding of the sense and level
      information for the interrupt.  This should be encoded based on
      the information in section 2) depending on the type of interrupt
      controller you have.
    - interrupt-parent : the phandle for the interrupt controller that
      services interrupts for this device.
    - num-channels : An integer representing the number of channels
      available.
    - channel-fifo-len : An integer representing the number of
      descriptor pointers each channel fetch fifo can hold.
    - exec-units-mask : The bitmask representing what execution units
      (EUs) are available. It's a single 32-bit cell. EU information
      should be encoded following the SEC's Descriptor Header Dword
      EU_SEL0 field documentation, i.e. as follows:

        bit 0 = reserved - should be 0
        bit 1 = set if SEC has the ARC4 EU (AFEU)
        bit 2 = set if SEC has the DES/3DES EU (DEU)
        bit 3 = set if SEC has the message digest EU (MDEU)
        bit 4 = set if SEC has the random number generator EU (RNG)
        bit 5 = set if SEC has the public key EU (PKEU)
        bit 6 = set if SEC has the AES EU (AESU)
        bit 7 = set if SEC has the Kasumi EU (KEU)

      bits 8 through 31 are reserved for future SEC EUs.

    - descriptor-types-mask : The bitmask representing what descriptors
      are available. It's a single 32-bit cell. Descriptor type
      information should be encoded following the SEC's Descriptor
      Header Dword DESC_TYPE field documentation, i.e. as follows:

        bit 0  = set if SEC supports the aesu_ctr_nonsnoop desc. type
        bit 1  = set if SEC supports the ipsec_esp descriptor type
        bit 2  = set if SEC supports the common_nonsnoop desc. type
        bit 3  = set if SEC supports the 802.11i AES ccmp desc. type
        bit 4  = set if SEC supports the hmac_snoop_no_afeu desc. type
        bit 5  = set if SEC supports the srtp descriptor type
        bit 6  = set if SEC supports the non_hmac_snoop_no_afeu desc.type
        bit 7  = set if SEC supports the pkeu_assemble descriptor type
        bit 8  = set if SEC supports the aesu_key_expand_output desc.type
        bit 9  = set if SEC supports the pkeu_ptmul descriptor type
        bit 10 = set if SEC supports the common_nonsnoop_afeu desc. type
        bit 11 = set if SEC supports the pkeu_ptadd_dbl descriptor type

      ..and so on and so forth.

   Example:

       /* MPC8548E */
       crypto@30000 {
               device_type = "crypto";
               model = "SEC2";
               compatible = "talitos";
               reg = <30000 10000>;
               interrupts = <1d 3>;
               interrupt-parent = <40000>;
               num-channels = <4>;
               channel-fifo-len = <18>;
               exec-units-mask = <000000fe>;
               descriptor-types-mask = <012b0ebf>;
       };

   h) Board Control and Status (BCSR)

   Required properties:

    - device_type : Should be "board-control"
    - reg : Offset and length of the register set for the device

    Example:

	bcsr@f8000000 {
		device_type = "board-control";
		reg = <f8000000 8000>;
	};

   i) Freescale QUICC Engine module (QE)
   This represents qe module that is installed on PowerQUICC II Pro.
   Hopefully it will merge backward compatibility with CPM/CPM2.
   Basically, it is a bus of devices, that could act more or less
   as a complete entity (UCC, USB etc ). All of them should be siblings on
   the "root" qe node, using the common properties from there.
   The description below applies to the qe of MPC8360 and
   more nodes and properties would be extended in the future.

   i) Root QE device

   Required properties:
   - device_type : should be "qe";
   - model : precise model of the QE, Can be "QE", "CPM", or "CPM2"
   - reg : offset and length of the device registers.
   - bus-frequency : the clock frequency for QUICC Engine.

   Recommended properties
   - brg-frequency : the internal clock source frequency for baud-rate
     generators in Hz.

   Example:
	qe@e0100000 {
		#address-cells = <1>;
		#size-cells = <1>;
		#interrupt-cells = <2>;
		device_type = "qe";
		model = "QE";
		ranges = <0 e0100000 00100000>;
		reg = <e0100000 480>;
		brg-frequency = <0>;
		bus-frequency = <179A7B00>;
	}


   ii) SPI (Serial Peripheral Interface)

   Required properties:
   - device_type : should be "spi".
   - compatible : should be "fsl_spi".
   - mode : the SPI operation mode, it can be "cpu" or "qe".
   - reg : Offset and length of the register set for the device
   - interrupts : <a b> where a is the interrupt number and b is a
     field that represents an encoding of the sense and level
     information for the interrupt.  This should be encoded based on
     the information in section 2) depending on the type of interrupt
     controller you have.
   - interrupt-parent : the phandle for the interrupt controller that
     services interrupts for this device.

   Example:
	spi@4c0 {
		device_type = "spi";
		compatible = "fsl_spi";
		reg = <4c0 40>;
		interrupts = <82 0>;
		interrupt-parent = <700>;
		mode = "cpu";
	};


   iii) USB (Universal Serial Bus Controller)

   Required properties:
   - device_type : should be "usb".
   - compatible : could be "qe_udc" or "fhci-hcd".
   - mode : the could be "host" or "slave".
   - reg : Offset and length of the register set for the device
   - interrupts : <a b> where a is the interrupt number and b is a
     field that represents an encoding of the sense and level
     information for the interrupt.  This should be encoded based on
     the information in section 2) depending on the type of interrupt
     controller you have.
   - interrupt-parent : the phandle for the interrupt controller that
     services interrupts for this device.

   Example(slave):
	usb@6c0 {
		device_type = "usb";
		compatible = "qe_udc";
		reg = <6c0 40>;
		interrupts = <8b 0>;
		interrupt-parent = <700>;
		mode = "slave";
	};


   iv) UCC (Unified Communications Controllers)

   Required properties:
   - device_type : should be "network", "hldc", "uart", "transparent"
    "bisync" or "atm".
   - compatible : could be "ucc_geth" or "fsl_atm" and so on.
   - model : should be "UCC".
   - device-id : the ucc number(1-8), corresponding to UCCx in UM.
   - reg : Offset and length of the register set for the device
   - interrupts : <a b> where a is the interrupt number and b is a
     field that represents an encoding of the sense and level
     information for the interrupt.  This should be encoded based on
     the information in section 2) depending on the type of interrupt
     controller you have.
   - interrupt-parent : the phandle for the interrupt controller that
     services interrupts for this device.
   - pio-handle : The phandle for the Parallel I/O port configuration.
   - rx-clock : represents the UCC receive clock source.
     0x00 : clock source is disabled;
     0x1~0x10 : clock source is BRG1~BRG16 respectively;
     0x11~0x28: clock source is QE_CLK1~QE_CLK24 respectively.
   - tx-clock: represents the UCC transmit clock source;
     0x00 : clock source is disabled;
     0x1~0x10 : clock source is BRG1~BRG16 respectively;
     0x11~0x28: clock source is QE_CLK1~QE_CLK24 respectively.

   Required properties for network device_type:
   - mac-address : list of bytes representing the ethernet address.
   - phy-handle : The phandle for the PHY connected to this controller.

   Recommended properties:
   - linux,network-index : This is the intended "index" of this
     network device.  This is used by the bootwrapper to interpret
     MAC addresses passed by the firmware when no information other
     than indices is available to associate an address with a device.
   - phy-connection-type : a string naming the controller/PHY interface type,
     i.e., "mii" (default), "rmii", "gmii", "rgmii", "rgmii-id", "tbi",
     or "rtbi".

   Example:
	ucc@2000 {
		device_type = "network";
		compatible = "ucc_geth";
		model = "UCC";
		device-id = <1>;
		reg = <2000 200>;
		interrupts = <a0 0>;
		interrupt-parent = <700>;
		mac-address = [ 00 04 9f 00 23 23 ];
		rx-clock = "none";
		tx-clock = "clk9";
		phy-handle = <212000>;
		phy-connection-type = "gmii";
		pio-handle = <140001>;
	};


   v) Parallel I/O Ports

   This node configures Parallel I/O ports for CPUs with QE support.
   The node should reside in the "soc" node of the tree.  For each
   device that using parallel I/O ports, a child node should be created.
   See the definition of the Pin configuration nodes below for more
   information.

   Required properties:
   - device_type : should be "par_io".
   - reg : offset to the register set and its length.
   - num-ports : number of Parallel I/O ports

   Example:
	par_io@1400 {
		reg = <1400 100>;
		#address-cells = <1>;
		#size-cells = <0>;
		device_type = "par_io";
		num-ports = <7>;
		ucc_pin@01 {
			......
		};


   vi) Pin configuration nodes

   Required properties:
   - linux,phandle : phandle of this node; likely referenced by a QE
     device.
   - pio-map : array of pin configurations.  Each pin is defined by 6
     integers.  The six numbers are respectively: port, pin, dir,
     open_drain, assignment, has_irq.
     - port : port number of the pin; 0-6 represent port A-G in UM.
     - pin : pin number in the port.
     - dir : direction of the pin, should encode as follows:

	0 = The pin is disabled
	1 = The pin is an output
	2 = The pin is an input
	3 = The pin is I/O

     - open_drain : indicates the pin is normal or wired-OR:

	0 = The pin is actively driven as an output
	1 = The pin is an open-drain driver. As an output, the pin is
	    driven active-low, otherwise it is three-stated.

     - assignment : function number of the pin according to the Pin Assignment
       tables in User Manual.  Each pin can have up to 4 possible functions in
       QE and two options for CPM.
     - has_irq : indicates if the pin is used as source of external
       interrupts.

   Example:
	ucc_pin@01 {
		linux,phandle = <140001>;
		pio-map = <
		/* port  pin  dir  open_drain  assignment  has_irq */
			0  3  1  0  1  0 	/* TxD0 */
			0  4  1  0  1  0 	/* TxD1 */
			0  5  1  0  1  0 	/* TxD2 */
			0  6  1  0  1  0 	/* TxD3 */
			1  6  1  0  3  0 	/* TxD4 */
			1  7  1  0  1  0 	/* TxD5 */
			1  9  1  0  2  0 	/* TxD6 */
			1  a  1  0  2  0 	/* TxD7 */
			0  9  2  0  1  0 	/* RxD0 */
			0  a  2  0  1  0 	/* RxD1 */
			0  b  2  0  1  0 	/* RxD2 */
			0  c  2  0  1  0 	/* RxD3 */
			0  d  2  0  1  0 	/* RxD4 */
			1  1  2  0  2  0 	/* RxD5 */
			1  0  2  0  2  0 	/* RxD6 */
			1  4  2  0  2  0 	/* RxD7 */
			0  7  1  0  1  0 	/* TX_EN */
			0  8  1  0  1  0 	/* TX_ER */
			0  f  2  0  1  0 	/* RX_DV */
			0  10 2  0  1  0 	/* RX_ER */
			0  0  2  0  1  0 	/* RX_CLK */
			2  9  1  0  3  0 	/* GTX_CLK - CLK10 */
			2  8  2  0  1  0>;	/* GTX125 - CLK9 */
	};

   vii) Multi-User RAM (MURAM)

   Required properties:
   - device_type : should be "muram".
   - mode : the could be "host" or "slave".
   - ranges : Should be defined as specified in 1) to describe the
      translation of MURAM addresses.
   - data-only : sub-node which defines the address area under MURAM
      bus that can be allocated as data/parameter

   Example:

	muram@10000 {
		device_type = "muram";
		ranges = <0 00010000 0000c000>;

		data-only@0{
			reg = <0 c000>;
		};
	};

    j) Flash chip nodes

    Flash chips (Memory Technology Devices) are often used for solid state
    file systems on embedded devices.

    Required properties:

     - device_type : has to be "rom"
     - compatible : Should specify what this flash device is compatible with.
       Currently, this is most likely to be "direct-mapped" (which
       corresponds to the MTD physmap mapping driver).
     - reg : Offset and length of the register set (or memory mapping) for
       the device.
     - bank-width : Width of the flash data bus in bytes. Required
       for the NOR flashes (compatible == "direct-mapped" and others) ONLY.

    Recommended properties :

     - partitions : Several pairs of 32-bit values where the first value is
       partition's offset from the start of the device and the second one is
       partition size in bytes with LSB used to signify a read only
       partition (so, the partition size should always be an even number).
     - partition-names : The list of concatenated zero terminated strings
       representing the partition names.
     - probe-type : The type of probe which should be done for the chip
       (JEDEC vs CFI actually). Valid ONLY for NOR flashes.

   Example:

 	flash@ff000000 {
 		device_type = "rom";
 		compatible = "direct-mapped";
 		probe-type = "CFI";
 		reg = <ff000000 01000000>;
 		bank-width = <4>;
 		partitions = <00000000 00f80000
 			      00f80000 00080001>;
 		partition-names = "fs\0firmware";
 	};

   More devices will be defined as this spec matures.

VII - Specifying interrupt information for devices
===================================================

The device tree represents the busses and devices of a hardware
system in a form similar to the physical bus topology of the
hardware.

In addition, a logical 'interrupt tree' exists which represents the
hierarchy and routing of interrupts in the hardware.

The interrupt tree model is fully described in the
document "Open Firmware Recommended Practice: Interrupt
Mapping Version 0.9".  The document is available at:
<http://playground.sun.com/1275/practice>.

1) interrupts property
----------------------

Devices that generate interrupts to a single interrupt controller
should use the conventional OF representation described in the
OF interrupt mapping documentation.

Each device which generates interrupts must have an 'interrupt'
property.  The interrupt property value is an arbitrary number of
of 'interrupt specifier' values which describe the interrupt or
interrupts for the device.

The encoding of an interrupt specifier is determined by the
interrupt domain in which the device is located in the
interrupt tree.  The root of an interrupt domain specifies in
its #interrupt-cells property the number of 32-bit cells
required to encode an interrupt specifier.  See the OF interrupt
mapping documentation for a detailed description of domains.

For example, the binding for the OpenPIC interrupt controller
specifies  an #interrupt-cells value of 2 to encode the interrupt
number and level/sense information. All interrupt children in an
OpenPIC interrupt domain use 2 cells per interrupt in their interrupts
property.

The PCI bus binding specifies a #interrupt-cell value of 1 to encode
which interrupt pin (INTA,INTB,INTC,INTD) is used.

2) interrupt-parent property
----------------------------

The interrupt-parent property is specified to define an explicit
link between a device node and its interrupt parent in
the interrupt tree.  The value of interrupt-parent is the
phandle of the parent node.

If the interrupt-parent property is not defined for a node, it's
interrupt parent is assumed to be an ancestor in the node's
_device tree_ hierarchy.

3) OpenPIC Interrupt Controllers
--------------------------------

OpenPIC interrupt controllers require 2 cells to encode
interrupt information.  The first cell defines the interrupt
number.  The second cell defines the sense and level
information.

Sense and level information should be encoded as follows:

	0 = low to high edge sensitive type enabled
	1 = active low level sensitive type enabled
	2 = active high level sensitive type enabled
	3 = high to low edge sensitive type enabled

4) ISA Interrupt Controllers
----------------------------

ISA PIC interrupt controllers require 2 cells to encode
interrupt information.  The first cell defines the interrupt
number.  The second cell defines the sense and level
information.

ISA PIC interrupt controllers should adhere to the ISA PIC
encodings listed below:

	0 =  active low level sensitive type enabled
	1 =  active high level sensitive type enabled
	2 =  high to low edge sensitive type enabled
	3 =  low to high edge sensitive type enabled


Appendix A - Sample SOC node for MPC8540
========================================

Note that the #address-cells and #size-cells for the SoC node
in this example have been explicitly listed; these are likely
not necessary as they are usually the same as the root node.

	soc8540@e0000000 {
		#address-cells = <1>;
		#size-cells = <1>;
		#interrupt-cells = <2>;
		device_type = "soc";
		ranges = <00000000 e0000000 00100000>
		reg = <e0000000 00003000>;
		bus-frequency = <0>;

		mdio@24520 {
			reg = <24520 20>;
			device_type = "mdio";
			compatible = "gianfar";

			ethernet-phy@0 {
				linux,phandle = <2452000>
				interrupt-parent = <40000>;
				interrupts = <35 1>;
				reg = <0>;
				device_type = "ethernet-phy";
			};

			ethernet-phy@1 {
				linux,phandle = <2452001>
				interrupt-parent = <40000>;
				interrupts = <35 1>;
				reg = <1>;
				device_type = "ethernet-phy";
			};

			ethernet-phy@3 {
				linux,phandle = <2452002>
				interrupt-parent = <40000>;
				interrupts = <35 1>;
				reg = <3>;
				device_type = "ethernet-phy";
			};

		};

		ethernet@24000 {
			#size-cells = <0>;
			device_type = "network";
			model = "TSEC";
			compatible = "gianfar";
			reg = <24000 1000>;
			mac-address = [ 00 E0 0C 00 73 00 ];
			interrupts = <d 3 e 3 12 3>;
			interrupt-parent = <40000>;
			phy-handle = <2452000>;
		};

		ethernet@25000 {
			#address-cells = <1>;
			#size-cells = <0>;
			device_type = "network";
			model = "TSEC";
			compatible = "gianfar";
			reg = <25000 1000>;
			mac-address = [ 00 E0 0C 00 73 01 ];
			interrupts = <13 3 14 3 18 3>;
			interrupt-parent = <40000>;
			phy-handle = <2452001>;
		};

		ethernet@26000 {
			#address-cells = <1>;
			#size-cells = <0>;
			device_type = "network";
			model = "FEC";
			compatible = "gianfar";
			reg = <26000 1000>;
			mac-address = [ 00 E0 0C 00 73 02 ];
			interrupts = <19 3>;
			interrupt-parent = <40000>;
			phy-handle = <2452002>;
		};

		serial@4500 {
			device_type = "serial";
			compatible = "ns16550";
			reg = <4500 100>;
			clock-frequency = <0>;
			interrupts = <1a 3>;
			interrupt-parent = <40000>;
		};

		pic@40000 {
			linux,phandle = <40000>;
			clock-frequency = <0>;
			interrupt-controller;
			#address-cells = <0>;
			reg = <40000 40000>;
			built-in;
			compatible = "chrp,open-pic";
			device_type = "open-pic";
                        big-endian;
		};

		i2c@3000 {
			interrupt-parent = <40000>;
			interrupts = <1b 3>;
			reg = <3000 18>;
			device_type = "i2c";
			compatible  = "fsl-i2c";
			dfsrr;
		};

	};