doc/usage/fit/source_file_format.rst

.. SPDX-License-Identifier: GPL-2.0+

Flattened Image Tree (FIT) Format
=================================

Introduction
------------

The number of elements playing a role in the kernel booting process has
increased over time and now typically includes the devicetree, kernel image and
possibly a ramdisk image. Generally, all must be placed in the system memory and
booted together.

For firmware images a similar process has taken place, with various binaries
loaded at different addresses, such as ARM's ATF, OpenSBI, FPGA and U-Boot
itself.

FIT provides a flexible and extensible format to deal with this complexity. It
provides support for multiple components. It also supports multiple
configurations, so that the same FIT can be used to boot multiple boards, with
some components in common (e.g. kernel) and some specific to that board (e.g.
devicetree).

Terminology
~~~~~~~~~~~

This document defines FIT by providing FDT (Flat Device Tree) bindings. These
describe the final form of the FIT at the moment when it is used. The user
perspective may be simpler, as some of the properties (like timestamps and
hashes) are filled in automatically by the U-Boot mkimage tool.

To avoid confusion with the kernel FDT the following naming convention is used:

FIT
    Flattened Image Tree

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

.its
    image tree source

.itb
    flattened image tree blob

Image-building procedure
~~~~~~~~~~~~~~~~~~~~~~~~

The following picture shows how the FIT 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). The resulting .itb file is the
actual binary of a new FIT::

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

Steps:

#. 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 FIT) is uploaded onto the target and used therein


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.


Root-node properties
--------------------

The root node of the FIT should have the following layout::

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

Optional property
~~~~~~~~~~~~~~~~~

description
    Textual description of the FIT

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 nodes
~~~~~~~~~~~~~~~

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.

configurations
    Contains a set of available configuration nodes and
    defines a default configuration.


'/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", "kernel_noload", "ramdisk", "firmware", "script",
    "filesystem", "flat_dt" and others (see uimage_type in common/image.c).

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". If the data is compressed but it should not be
    uncompressed by U-Boot (e.g. compressed ramdisk), this should also be set
    to "none".

Conditionally mandatory property
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

os
    OS name, mandatory for types "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",
    "sandbox".

entry
    entry point address, address size is determined by
    '#address-cells' property of the root node.
    Mandatory for types: "firmware", and "kernel".

load
    load address, address size is determined by '#address-cells'
    property of the root node.
    Mandatory for types: "firmware", and "kernel".

compatible
    compatible method for loading image.
    Mandatory for types: "fpga", and images that do not specify a load address.
    Supported compatible methods:

    "u-boot,fpga-legacy"
        the generic fpga loading routine.

    "u-boot,zynqmp-fpga-ddrauth"
        signed non-encrypted FPGA bitstream for
        Xilinx Zynq UltraScale+ (ZymqMP) device.

    "u-boot,zynqmp-fpga-enc"
        encrypted FPGA bitstream for Xilinx Zynq

    UltraScale+ (ZynqMP) device.

phase
    U-Boot phase for which the image is intended.

    "spl"
        image is an SPL image

    "u-boot"
        image is a U-Boot image

Optional nodes:

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


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.


'/configurations' node
----------------------

The 'configurations' node creates convenient, labeled boot configurations,
which combine together kernel images with their ramdisks and fdt blobs.

The 'configurations' node 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.


Configuration nodes
-------------------

Each configuration has the following structure::

    o config-1
        |- description = "configuration description"
        |- kernel = "kernel sub-node unit name"
        |- fdt = "fdt sub-node unit-name" [, "fdt overlay sub-node unit-name", ...]
        |- loadables = "loadables sub-node unit-name"
        |- script = "
        |- compatible = "vendor,board-style device tree compatible string"


Mandatory properties
~~~~~~~~~~~~~~~~~~~~

description
    Textual configuration description.

kernel or firmware
    Unit name of the corresponding kernel or firmware
    (u-boot, op-tee, etc) image. If both "kernel" and "firmware" are specified,
    control is passed to the firmware image.

Optional properties
~~~~~~~~~~~~~~~~~~~

fdt
    Unit name of the corresponding fdt blob (component image node of a
    "fdt type"). Additional fdt overlay nodes can be supplied which signify
    that the resulting device tree blob is generated by the first base fdt
    blob with all subsequent overlays applied.

fpga
    Unit name of the corresponding fpga bitstream blob
    (component image node of a "fpga type").

loadables
    Unit name containing a list of additional binaries to be
    loaded at their given locations.  "loadables" is a comma-separated list
    of strings. U-Boot will load each binary at its given start-address and
    may optionally invoke additional post-processing steps on this binary based
    on its component image node type.

script
    The image to use when loading a U-Boot script (for use with the
    source command).

compatible
    The root compatible string of the U-Boot device tree that
    this configuration shall automatically match when CONFIG_FIT_BEST_MATCH is
    enabled. If this property is not provided, the compatible string will be
    extracted from the fdt blob instead. This is only possible if the fdt is
    not compressed, so images with compressed fdts that want to use compatible
    string matching must always provide this property.

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.


External data
-------------

The above format shows a 'data' property which holds the data for each image.
It is also possible for this data to reside outside the FIT itself. This
allows the FIT to be quite small, so that it can be loaded and scanned
without loading a large amount of data. Then when an image is needed it can
be loaded from an external source.

In this case the 'data' property is omitted. Instead you can use:

data-offset
    offset of the data in a separate image store. The image
    store is placed immediately after the last byte of the device tree binary,
    aligned to a 4-byte boundary.

data-size
    size of the data in bytes

The 'data-offset' property can be substituted with 'data-position', which
defines an absolute position or address as the offset. This is helpful when
booting U-Boot proper before performing relocation. Pass '-p [offset]' to
mkimage to enable 'data-position'.

Normal kernel FIT image has data embedded within FIT structure. U-Boot image
for SPL boot has external data. Existence of 'data-offset' can be used to
identify which format is used.

For FIT image with external data, it would be better to align each blob of data
to block(512 byte) for block device, so that we don't need to do the copy when
read the image data in SPL. Pass '-B 0x200' to mkimage to align the FIT
structure and data to 512 byte, other values available for other align size.

Examples
--------

Some example files are available here, showing various scenarios

.. toctree::
    :maxdepth: 1

    kernel
    kernel_fdt
    kernel_fdts_compressed
    kernel
    multi
    multi_spl
    multi-with-fpga
    multi-with-loadables
    sec_firmware_ppa
    sign-configs
    sign-images
    uefi
    update3
    update_uboot

.. sectionauthor:: Marian Balakowicz <m8@semihalf.com>
.. sectionauthor:: External data additions, 25/1/16 Simon Glass <sjg@chromium.org>