doc/uImage.FIT/source_file_format.txt - github/trini/u-boot - Gitiles

 U-boot new uImage source file format (bindings definition)
 ==========================================================

 Author: Marian Balakowicz <m8@semihalf.com>

 1) Introduction
 ---------------

 Evolution of the 2.6 Linux kernel for embedded PowerPC systems introduced new
 booting method which requires that hardware description is available to the
 kernel in the form of Flattened Device Tree.

 Booting with a Flattened Device Tree is much more flexible and is intended to
 replace direct passing of 'struct bd_info' which was used to boot pre-FDT
 kernels.

 However, U-boot needs to support both techniques to provide backward
 compatibility for platforms which are not FDT ready. Number of elements
 playing role in the booting process has increased and now includes the FDT
 blob. Kernel image, FDT blob and possibly ramdisk image - all must be placed
 in the system memory and passed to bootm as a arguments. Some of them may be
 missing: FDT is not present for legacy platforms, ramdisk is always optional.
 Additionally, old uImage format has been extended to support multi sub-images
 but the support is limited by simple format of the legacy uImage structure.
 Single binary header 'struct image_header' is not flexible enough to cover all
 possible scenarios.

 All those factors combined clearly show that there is a need for new, more
 flexible, multi component uImage format.


 2) New uImage format assumptions
 --------------------------------

 a) Implementation

 Libfdt has been selected for the new uImage format implementation as (1) it
 provides needed functionality, (2) is actively maintained and developed and
 (3) increases code reuse as it is already part of the U-boot source tree.

 b) Terminology

 This document defines new uImage structure by providing FDT bindings for new
 uImage internals. Bindings are defined from U-boot perspective, i.e. describe
 final form of the uImage at the moment when it reaches U-boot. User
 perspective may be simpler, as some of the properties (like timestamps and
 hashes) will need to be filled in automatically by the U-boot mkimage tool.

 To avoid confusion with the kernel FDT the following naming convention is
 proposed for the new uImage format related terms:

 FIT	- Flattened uImage Tree

 FIT is formally a flattened device tree (in the libfdt meaning), which
 conforms to bindings defined in this document.

 .its	- image tree source
 .itb	- image tree blob

 c) Image building procedure

 The following picture shows how the new uImage is prepared. Input consists of
 image source file (.its) and a set of data files. Image is created with the
 help of standard U-boot mkimage tool which in turn uses dtc (device tree
 compiler) to produce image tree blob (.itb).  Resulting .itb file is the
 actual binary of a new uImage.


 tqm5200.its
 +
 vmlinux.bin.gz	   mkimage + dtc	       xfer to target
 eldk-4.2-ramdisk  --------------> tqm5200.itb --------------> bootm
 tqm5200.dtb			     /|\
 ...				      |
 				 'new uImage'

 	- create .its file, automatically filled-in properties are omitted
 	- call mkimage tool on a .its file
 	- mkimage calls dtc to create .itb image and assures that
 	  missing properties are added
 	- .itb (new uImage) is uploaded onto the target and used therein


 d) Unique identifiers

 To identify FIT sub-nodes representing images, hashes, configurations (which
 are defined in the following sections), the "unit name" of the given sub-node
 is used as it's identifier as it assures uniqueness without additional
 checking required.


 3) Root node properties
 -----------------------

 Root node of the uImage Tree should have the following layout:

 / o image-tree
     |- description = "image description"
     |- timestamp = <12399321>
     |- #address-cells = <1>
     |
     o images
     | |
     | o img@1 {...}
     | o img@2 {...}
     | ...
     |
     o configurations
       |- default = "cfg@1"
       |
       o cfg@1 {...}
       o cfg@2 {...}
       ...


   Optional property:
   - description : Textual description of the uImage

   Mandatory property:
   - timestamp : Last image modification time being counted in seconds since
     1970-01-01 00:00:00 - to be automatically calculated by mkimage tool.

   Conditionally mandatory property:
   - #address-cells : Number of 32bit cells required to represent entry and
     load addresses supplied within sub-image nodes. May be omitted when no
     entry or load addresses are used.

   Mandatory node:
   - images : This node contains a set of sub-nodes, each of them representing
     single component sub-image (like kernel, ramdisk, etc.). At least one
     sub-image is required.

   Optional node:
   - configurations : Contains a set of available configuration nodes and
     defines a default configuration.


 4) '/images' node
 -----------------

 This node is a container node for component sub-image nodes. Each sub-node of
 the '/images' node should have the following layout:

  o image@1
    |- description = "component sub-image description"
    |- data = /incbin/("path/to/data/file.bin")
    |- type = "sub-image type name"
    |- arch = "ARCH name"
    |- os = "OS name"
    |- compression = "compression name"
    |- load = <00000000>
    |- entry = <00000000>
    |
    o hash@1 {...}
    o hash@2 {...}
    ...

   Mandatory properties:
   - description : Textual description of the component sub-image
   - type : Name of component sub-image type, supported types are:
     "standalone", "kernel", "ramdisk", "firmware", "script", "filesystem",
     "fdt".
   - data : Path to the external file which contains this node's binary data.
   - compression : Compression used by included data. Supported compressions
     are "gzip" and "bzip2". If no compression is used compression property
     should be set to "none".

   Conditionally mandatory property:
   - os : OS name, mandatory for type="kernel", valid OS names are: "openbsd",
     "netbsd", "freebsd", "4_4bsd", "linux", "svr4", "esix", "solaris", "irix",
     "sco", "dell", "ncr", "lynxos", "vxworks", "psos", "qnx", "u_boot",
     "rtems", "unity", "integrity".
   - arch : Architecture name, mandatory for types: "standalone", "kernel",
     "firmware", "ramdisk" and "fdt". Valid architecture names are: "alpha",
     "arm", "i386", "ia64", "mips", "mips64", "ppc", "s390", "sh", "sparc",
     "sparc64", "m68k", "microblaze", "nios2", "blackfin", "avr32", "st200".
   - entry : entry point address, address size is determined by
     '#address-cells' property of the root node. Mandatory for for types:
     "standalone" and "kernel".
   - load : load address, address size is determined by '#address-cells'
     property of the root node. Mandatory for types: "standalone" and "kernel".

   Optional nodes:
   - hash@1 : Each hash sub-node represents separate hash or checksum
     calculated for node's data according to specified algorithm.


 5) Hash nodes
 -------------

 o hash@1
   |- algo = "hash or checksum algorithm name"
   |- value = [hash or checksum value]

   Mandatory properties:
   - algo : Algorithm name, supported are "crc32", "md5" and "sha1".
   - value : Actual checksum or hash value, correspondingly 4, 16 or 20 bytes
     long.


 6) '/configurations' node
 -------------------------

 The 'configurations' node is optional. If present, it allows to create a
 convenient, labeled boot configurations, which combine together kernel images
 with their ramdisks and fdt blobs.

 The 'configurations' node has has the following structure:

 o configurations
   |- default = "default configuration sub-node unit name"
   |
   o config@1 {...}
   o config@2 {...}
   ...


   Optional property:
   - default : Selects one of the configuration sub-nodes as a default
     configuration.

   Mandatory nodes:
   - configuration-sub-node-unit-name : At least one of the configuration
     sub-nodes is required.


 7) Configuration nodes
 ----------------------

 Each configuration has the following structure:

 o config@1
   |- description = "configuration description"
   |- kernel = "kernel sub-node unit name"
   |- ramdisk = "ramdisk sub-node unit name"
   |- fdt = "fdt sub-node unit-name"


   Mandatory properties:
   - description : Textual configuration description.
   - kernel : Unit name of the corresponding kernel image (image sub-node of a
     "kernel" type).

   Optional properties:
   - ramdisk : Unit name of the corresponding ramdisk image (component image
     node of a "ramdisk" type).
   - fdt : Unit name of the corresponding fdt blob (component image node of a
     "fdt type").

 The FDT blob is required to properly boot FDT based kernel, so the minimal
 configuration for 2.6 FDT kernel is (kernel, fdt) pair.

 Older, 2.4 kernel and 2.6 non-FDT kernel do not use FDT blob, in such cases
 'struct bd_info' must be passed instead of FDT blob, thus fdt property *must
 not* be specified in a configuration node.


 8) Examples
 -----------

 Please see doc/uImage.FIT/*.its for actual image source files.
	U-boot new uImage source file format (bindings definition)
	==========================================================

	Author: Marian Balakowicz <m8@semihalf.com>

	1) Introduction
	---------------

	Evolution of the 2.6 Linux kernel for embedded PowerPC systems introduced new
	booting method which requires that hardware description is available to the
	kernel in the form of Flattened Device Tree.

	Booting with a Flattened Device Tree is much more flexible and is intended to
	replace direct passing of 'struct bd_info' which was used to boot pre-FDT
	kernels.

	However, U-boot needs to support both techniques to provide backward
	compatibility for platforms which are not FDT ready. Number of elements
	playing role in the booting process has increased and now includes the FDT
	blob. Kernel image, FDT blob and possibly ramdisk image - all must be placed
	in the system memory and passed to bootm as a arguments. Some of them may be
	missing: FDT is not present for legacy platforms, ramdisk is always optional.
	Additionally, old uImage format has been extended to support multi sub-images
	but the support is limited by simple format of the legacy uImage structure.
	Single binary header 'struct image_header' is not flexible enough to cover all
	possible scenarios.

	All those factors combined clearly show that there is a need for new, more
	flexible, multi component uImage format.


	2) New uImage format assumptions
	--------------------------------

	a) Implementation

	Libfdt has been selected for the new uImage format implementation as (1) it
	provides needed functionality, (2) is actively maintained and developed and
	(3) increases code reuse as it is already part of the U-boot source tree.

	b) Terminology

	This document defines new uImage structure by providing FDT bindings for new
	uImage internals. Bindings are defined from U-boot perspective, i.e. describe
	final form of the uImage at the moment when it reaches U-boot. User
	perspective may be simpler, as some of the properties (like timestamps and
	hashes) will need to be filled in automatically by the U-boot mkimage tool.

	To avoid confusion with the kernel FDT the following naming convention is
	proposed for the new uImage format related terms:

	FIT - Flattened uImage Tree

	FIT is formally a flattened device tree (in the libfdt meaning), which
	conforms to bindings defined in this document.

	.its - image tree source
	.itb - image tree blob

	c) Image building procedure

	The following picture shows how the new uImage is prepared. Input consists of
	image source file (.its) and a set of data files. Image is created with the
	help of standard U-boot mkimage tool which in turn uses dtc (device tree
	compiler) to produce image tree blob (.itb). Resulting .itb file is the
	actual binary of a new uImage.


	tqm5200.its
	+
	vmlinux.bin.gz mkimage + dtc xfer to target
	eldk-4.2-ramdisk --------------> tqm5200.itb --------------> bootm
	tqm5200.dtb /\|\
	... \|
	'new uImage'

	- create .its file, automatically filled-in properties are omitted
	- call mkimage tool on a .its file
	- mkimage calls dtc to create .itb image and assures that
	missing properties are added
	- .itb (new uImage) is uploaded onto the target and used therein


	d) Unique identifiers

	To identify FIT sub-nodes representing images, hashes, configurations (which
	are defined in the following sections), the "unit name" of the given sub-node
	is used as it's identifier as it assures uniqueness without additional
	checking required.


	3) Root node properties
	-----------------------

	Root node of the uImage Tree should have the following layout:

	/ o image-tree
	\|- description = "image description"
	\|- timestamp = <12399321>
	\|- #address-cells = <1>
	\|
	o images
	\| \|
	\| o img@1 {...}
	\| o img@2 {...}
	\| ...
	\|
	o configurations
	\|- default = "cfg@1"
	\|
	o cfg@1 {...}
	o cfg@2 {...}
	...


	Optional property:
	- description : Textual description of the uImage

	Mandatory property:
	- timestamp : Last image modification time being counted in seconds since
	1970-01-01 00:00:00 - to be automatically calculated by mkimage tool.

	Conditionally mandatory property:
	- #address-cells : Number of 32bit cells required to represent entry and
	load addresses supplied within sub-image nodes. May be omitted when no
	entry or load addresses are used.

	Mandatory node:
	- images : This node contains a set of sub-nodes, each of them representing
	single component sub-image (like kernel, ramdisk, etc.). At least one
	sub-image is required.

	Optional node:
	- configurations : Contains a set of available configuration nodes and
	defines a default configuration.


	4) '/images' node
	-----------------

	This node is a container node for component sub-image nodes. Each sub-node of
	the '/images' node should have the following layout:

	o image@1
	\|- description = "component sub-image description"
	\|- data = /incbin/("path/to/data/file.bin")
	\|- type = "sub-image type name"
	\|- arch = "ARCH name"
	\|- os = "OS name"
	\|- compression = "compression name"
	\|- load = <00000000>
	\|- entry = <00000000>
	\|
	o hash@1 {...}
	o hash@2 {...}
	...

	Mandatory properties:
	- description : Textual description of the component sub-image
	- type : Name of component sub-image type, supported types are:
	"standalone", "kernel", "ramdisk", "firmware", "script", "filesystem",
	"fdt".
	- data : Path to the external file which contains this node's binary data.
	- compression : Compression used by included data. Supported compressions
	are "gzip" and "bzip2". If no compression is used compression property
	should be set to "none".

	Conditionally mandatory property:
	- os : OS name, mandatory for type="kernel", valid OS names are: "openbsd",
	"netbsd", "freebsd", "4_4bsd", "linux", "svr4", "esix", "solaris", "irix",
	"sco", "dell", "ncr", "lynxos", "vxworks", "psos", "qnx", "u_boot",
	"rtems", "unity", "integrity".
	- arch : Architecture name, mandatory for types: "standalone", "kernel",
	"firmware", "ramdisk" and "fdt". Valid architecture names are: "alpha",
	"arm", "i386", "ia64", "mips", "mips64", "ppc", "s390", "sh", "sparc",
	"sparc64", "m68k", "microblaze", "nios2", "blackfin", "avr32", "st200".
	- entry : entry point address, address size is determined by
	'#address-cells' property of the root node. Mandatory for for types:
	"standalone" and "kernel".
	- load : load address, address size is determined by '#address-cells'
	property of the root node. Mandatory for types: "standalone" and "kernel".

	Optional nodes:
	- hash@1 : Each hash sub-node represents separate hash or checksum
	calculated for node's data according to specified algorithm.


	5) Hash nodes
	-------------

	o hash@1
	\|- algo = "hash or checksum algorithm name"
	\|- value = [hash or checksum value]

	Mandatory properties:
	- algo : Algorithm name, supported are "crc32", "md5" and "sha1".
	- value : Actual checksum or hash value, correspondingly 4, 16 or 20 bytes
	long.


	6) '/configurations' node
	-------------------------

	The 'configurations' node is optional. If present, it allows to create a
	convenient, labeled boot configurations, which combine together kernel images
	with their ramdisks and fdt blobs.

	The 'configurations' node has has the following structure:

	o configurations
	\|- default = "default configuration sub-node unit name"
	\|
	o config@1 {...}
	o config@2 {...}
	...


	Optional property:
	- default : Selects one of the configuration sub-nodes as a default
	configuration.

	Mandatory nodes:
	- configuration-sub-node-unit-name : At least one of the configuration
	sub-nodes is required.


	7) Configuration nodes
	----------------------

	Each configuration has the following structure:

	o config@1
	\|- description = "configuration description"
	\|- kernel = "kernel sub-node unit name"
	\|- ramdisk = "ramdisk sub-node unit name"
	\|- fdt = "fdt sub-node unit-name"


	Mandatory properties:
	- description : Textual configuration description.
	- kernel : Unit name of the corresponding kernel image (image sub-node of a
	"kernel" type).

	Optional properties:
	- ramdisk : Unit name of the corresponding ramdisk image (component image
	node of a "ramdisk" type).
	- fdt : Unit name of the corresponding fdt blob (component image node of a
	"fdt type").

	The FDT blob is required to properly boot FDT based kernel, so the minimal
	configuration for 2.6 FDT kernel is (kernel, fdt) pair.

	Older, 2.4 kernel and 2.6 non-FDT kernel do not use FDT blob, in such cases
	'struct bd_info' must be passed instead of FDT blob, thus fdt property *must
	not* be specified in a configuration node.


	8) Examples
	-----------

	Please see doc/uImage.FIT/*.its for actual image source files.