doc/uImage.FIT/source_file_format.txt

   1 U-Boot new uImage source file format (bindings definition)
   2 ==========================================================
   3
   4 Author: Marian Balakowicz <m8@semihalf.com>
   5 External data additions, 25/1/16 Simon Glass <sjg@chromium.org>
   6
   7 1) Introduction
   8 ---------------
   9
  10 Evolution of the 2.6 Linux kernel for embedded PowerPC systems introduced new
  11 booting method which requires that hardware description is available to the
  12 kernel in the form of Flattened Device Tree.
  13
  14 Booting with a Flattened Device Tree is much more flexible and is intended to
  15 replace direct passing of 'struct bd_info' which was used to boot pre-FDT
  16 kernels.
  17
  18 However, U-Boot needs to support both techniques to provide backward
  19 compatibility for platforms which are not FDT ready. Number of elements
  20 playing role in the booting process has increased and now includes the FDT
  21 blob. Kernel image, FDT blob and possibly ramdisk image - all must be placed
  22 in the system memory and passed to bootm as a arguments. Some of them may be
  23 missing: FDT is not present for legacy platforms, ramdisk is always optional.
  24 Additionally, old uImage format has been extended to support multi sub-images
  25 but the support is limited by simple format of the legacy uImage structure.
  26 Single binary header 'struct image_header' is not flexible enough to cover all
  27 possible scenarios.
  28
  29 All those factors combined clearly show that there is a need for new, more
  30 flexible, multi component uImage format.
  31
  32
  33 2) New uImage format assumptions
  34 --------------------------------
  35
  36 a) Implementation
  37
  38 Libfdt has been selected for the new uImage format implementation as (1) it
  39 provides needed functionality, (2) is actively maintained and developed and
  40 (3) increases code reuse as it is already part of the U-Boot source tree.
  41
  42 b) Terminology
  43
  44 This document defines new uImage structure by providing FDT bindings for new
  45 uImage internals. Bindings are defined from U-Boot perspective, i.e. describe
  46 final form of the uImage at the moment when it reaches U-Boot. User
  47 perspective may be simpler, as some of the properties (like timestamps and
  48 hashes) will need to be filled in automatically by the U-Boot mkimage tool.
  49
  50 To avoid confusion with the kernel FDT the following naming convention is
  51 proposed for the new uImage format related terms:
  52
  53 FIT     - Flattened uImage Tree
  54
  55 FIT is formally a flattened device tree (in the libfdt meaning), which
  56 conforms to bindings defined in this document.
  57
  58 .its    - image tree source
  59 .itb    - flattened image tree blob
  60
  61 c) Image building procedure
  62
  63 The following picture shows how the new uImage is prepared. Input consists of
  64 image source file (.its) and a set of data files. Image is created with the
  65 help of standard U-Boot mkimage tool which in turn uses dtc (device tree
  66 compiler) to produce image tree blob (.itb).  Resulting .itb file is the
  67 actual binary of a new uImage.
  68
  69
  70 tqm5200.its
  71 +
  72 vmlinux.bin.gz     mkimage + dtc               xfer to target
  73 eldk-4.2-ramdisk  --------------> tqm5200.itb --------------> bootm
  74 tqm5200.dtb                          /|\
  75 ...                                   |
  76                                  'new uImage'
  77
  78         - create .its file, automatically filled-in properties are omitted
  79         - call mkimage tool on a .its file
  80         - mkimage calls dtc to create .itb image and assures that
  81           missing properties are added
  82         - .itb (new uImage) is uploaded onto the target and used therein
  83
  84
  85 d) Unique identifiers
  86
  87 To identify FIT sub-nodes representing images, hashes, configurations (which
  88 are defined in the following sections), the "unit name" of the given sub-node
  89 is used as it's identifier as it assures uniqueness without additional
  90 checking required.
  91
  92
  93 3) Root node properties
  94 -----------------------
  95
  96 Root node of the uImage Tree should have the following layout:
  97
  98 / o image-tree
  99     |- description = "image description"
 100     |- timestamp = <12399321>
 101     |- #address-cells = <1>
 102     |
 103     o images
 104     | |
 105     | o image@1 {...}
 106     | o image@2 {...}
 107     | ...
 108     |
 109     o configurations
 110       |- default = "conf@1"
 111       |
 112       o conf@1 {...}
 113       o conf@2 {...}
 114       ...
 115
 116
 117   Optional property:
 118   - description : Textual description of the uImage
 119
 120   Mandatory property:
 121   - timestamp : Last image modification time being counted in seconds since
 122     1970-01-01 00:00:00 - to be automatically calculated by mkimage tool.
 123
 124   Conditionally mandatory property:
 125   - #address-cells : Number of 32bit cells required to represent entry and
 126     load addresses supplied within sub-image nodes. May be omitted when no
 127     entry or load addresses are used.
 128
 129   Mandatory node:
 130   - images : This node contains a set of sub-nodes, each of them representing
 131     single component sub-image (like kernel, ramdisk, etc.). At least one
 132     sub-image is required.
 133
 134   Optional node:
 135   - configurations : Contains a set of available configuration nodes and
 136     defines a default configuration.
 137
 138
 139 4) '/images' node
 140 -----------------
 141
 142 This node is a container node for component sub-image nodes. Each sub-node of
 143 the '/images' node should have the following layout:
 144
 145  o image@1
 146    |- description = "component sub-image description"
 147    |- data = /incbin/("path/to/data/file.bin")
 148    |- type = "sub-image type name"
 149    |- arch = "ARCH name"
 150    |- os = "OS name"
 151    |- compression = "compression name"
 152    |- load = <00000000>
 153    |- entry = <00000000>
 154    |
 155    o hash@1 {...}
 156    o hash@2 {...}
 157    ...
 158
 159   Mandatory properties:
 160   - description : Textual description of the component sub-image
 161   - type : Name of component sub-image type, supported types are:
 162     "standalone", "kernel", "kernel_noload", "ramdisk", "firmware", "script",
 163     "filesystem", "flat_dt" and others (see uimage_type in common/image.c).
 164   - data : Path to the external file which contains this node's binary data.
 165   - compression : Compression used by included data. Supported compressions
 166     are "gzip" and "bzip2". If no compression is used compression property
 167     should be set to "none".
 168
 169   Conditionally mandatory property:
 170   - os : OS name, mandatory for types "kernel" and "ramdisk". Valid OS names
 171     are: "openbsd", "netbsd", "freebsd", "4_4bsd", "linux", "svr4", "esix",
 172     "solaris", "irix", "sco", "dell", "ncr", "lynxos", "vxworks", "psos", "qnx",
 173     "u_boot", "rtems", "unity", "integrity".
 174   - arch : Architecture name, mandatory for types: "standalone", "kernel",
 175     "firmware", "ramdisk" and "fdt". Valid architecture names are: "alpha",
 176     "arm", "i386", "ia64", "mips", "mips64", "ppc", "s390", "sh", "sparc",
 177     "sparc64", "m68k", "microblaze", "nios2", "blackfin", "avr32", "st200",
 178     "sandbox".
 179   - entry : entry point address, address size is determined by
 180     '#address-cells' property of the root node. Mandatory for for types:
 181     "standalone" and "kernel".
 182   - load : load address, address size is determined by '#address-cells'
 183     property of the root node. Mandatory for types: "standalone" and "kernel".
 184
 185   Optional nodes:
 186   - hash@1 : Each hash sub-node represents separate hash or checksum
 187     calculated for node's data according to specified algorithm.
 188
 189
 190 5) Hash nodes
 191 -------------
 192
 193 o hash@1
 194   |- algo = "hash or checksum algorithm name"
 195   |- value = [hash or checksum value]
 196
 197   Mandatory properties:
 198   - algo : Algorithm name, supported are "crc32", "md5" and "sha1".
 199   - value : Actual checksum or hash value, correspondingly 4, 16 or 20 bytes
 200     long.
 201
 202
 203 6) '/configurations' node
 204 -------------------------
 205
 206 The 'configurations' node is optional. If present, it allows to create a
 207 convenient, labeled boot configurations, which combine together kernel images
 208 with their ramdisks and fdt blobs.
 209
 210 The 'configurations' node has has the following structure:
 211
 212 o configurations
 213   |- default = "default configuration sub-node unit name"
 214   |
 215   o config@1 {...}
 216   o config@2 {...}
 217   ...
 218
 219
 220   Optional property:
 221   - default : Selects one of the configuration sub-nodes as a default
 222     configuration.
 223
 224   Mandatory nodes:
 225   - configuration-sub-node-unit-name : At least one of the configuration
 226     sub-nodes is required.
 227
 228
 229 7) Configuration nodes
 230 ----------------------
 231
 232 Each configuration has the following structure:
 233
 234 o config@1
 235   |- description = "configuration description"
 236   |- kernel = "kernel sub-node unit name"
 237   |- ramdisk = "ramdisk sub-node unit name"
 238   |- fdt = "fdt sub-node unit-name" [, "fdt overlay sub-node unit-name", ...]
 239   |- fpga = "fpga sub-node unit-name"
 240   |- loadables = "loadables sub-node unit-name"
 241
 242
 243   Mandatory properties:
 244   - description : Textual configuration description.
 245   - kernel : Unit name of the corresponding kernel image (image sub-node of a
 246     "kernel" type).
 247
 248   Optional properties:
 249   - ramdisk : Unit name of the corresponding ramdisk image (component image
 250     node of a "ramdisk" type).
 251   - fdt : Unit name of the corresponding fdt blob (component image node of a
 252     "fdt type"). Additional fdt overlay nodes can be supplied which signify
 253     that the resulting device tree blob is generated by the first base fdt
 254     blob with all subsequent overlays applied.
 255   - setup : Unit name of the corresponding setup binary (used for booting
 256     an x86 kernel). This contains the setup.bin file built by the kernel.
 257   - fpga : Unit name of the corresponding fpga bitstream blob
 258     (component image node of a "fpga type").
 259   - loadables : Unit name containing a list of additional binaries to be
 260     loaded at their given locations.  "loadables" is a comma-separated list
 261     of strings. U-Boot will load each binary at its given start-address and
 262     may optionaly invoke additional post-processing steps on this binary based
 263     on its component image node type.
 264
 265 The FDT blob is required to properly boot FDT based kernel, so the minimal
 266 configuration for 2.6 FDT kernel is (kernel, fdt) pair.
 267
 268 Older, 2.4 kernel and 2.6 non-FDT kernel do not use FDT blob, in such cases
 269 'struct bd_info' must be passed instead of FDT blob, thus fdt property *must
 270 not* be specified in a configuration node.
 271
 272
 273 8) External data
 274 ----------------
 275
 276 The above format shows a 'data' property which holds the data for each image.
 277 It is also possible for this data to reside outside the FIT itself. This
 278 allows the FIT to be quite small, so that it can be loaded and scanned
 279 without loading a large amount of data. Then when an image is needed it can
 280 be loaded from an external source.
 281
 282 In this case the 'data' property is omitted. Instead you can use:
 283
 284   - data-offset : offset of the data in a separate image store. The image
 285     store is placed immediately after the last byte of the device tree binary,
 286     aligned to a 4-byte boundary.
 287   - data-size : size of the data in bytes
 288
 289 The 'data-offset' property can be substituted with 'data-position', which
 290 defines an absolute position or address as the offset. This is helpful when
 291 booting U-Boot proper before performing relocation. Pass '-p [offset]' to
 292 mkimage to enable 'data-position'.
 293
 294 Normal kernel FIT image has data embedded within FIT structure. U-Boot image
 295 for SPL boot has external data. Existence of 'data-offset' can be used to
 296 identify which format is used.
 297
 298 9) Examples
 299 -----------
 300
 301 Please see doc/uImage.FIT/*.its for actual image source files.