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The kernel tree builds some "composite" DTBs, where the final DTB is the
result of applying one or more DTB overlays on top of a base DTB with
fdtoverlay.
The FIT image specification already supports configurations having one
base DTB and overlays applied on top. It is then up to the bootloader to
apply said overlays and either use or pass on the final result. This
allows the FIT image builder to reuse the same FDT images for multiple
configurations, if such cases exist.
The decomposition function depends on the kernel build system, reading
back the .cmd files for the to-be-packaged DTB files to check for the
fdtoverlay command being called. This will not work outside the kernel
tree. The function is off by default to keep compatibility with possible
existing users.
To facilitate the decomposition and keep the code clean, the model and
compatitble string extraction have been moved out of the output_dtb
function. The FDT image description is replaced with the base file name
of the included image.
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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According to the FIT image source file format document found in U-boot [1]
and the split-out FIT image specification [2], under "'/images' node" ->
"Conditionally mandatory property", the "compatible" property is described
as "compatible method for loading image", i.e., not the compatible string
embedded in the FDT or used for matching.
Drop the compatible string from the fdt image entry node.
While at it also fix up a typo in the document section of output_dtb.
[1] U-boot source "doc/usage/fit/source_file_format.rst", or on the website:
https://docs.u-boot.org/en/latest/usage/fit/source_file_format.html
[2] https://github.com/open-source-firmware/flat-image-tree/blob/main/source/chapter2-source-file-format.rst
Fixes: 7a23b027ec17 ("arm64: boot: Support Flat Image Tree")
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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Add a script which produces a Flat Image Tree (FIT), a single file
containing the built kernel and associated devicetree files.
Compression defaults to gzip which gives a good balance of size and
performance.
The files compress from about 86MB to 24MB using this approach.
The FIT can be used by bootloaders which support it, such as U-Boot
and Linuxboot. It permits automatic selection of the correct
devicetree, matching the compatible string of the running board with
the closest compatible string in the FIT. There is no need for
filenames or other workarounds.
Add a 'make image.fit' build target for arm64, as well.
The FIT can be examined using 'dumpimage -l'.
This uses the 'dtbs-list' file but processes only .dtb files, ignoring
the overlay .dtbo files.
This features requires pylibfdt (use 'pip install libfdt'). It also
requires compression utilities for the algorithm being used. Supported
compression options are the same as the Image.xxx files. Use
FIT_COMPRESSION to select an algorithm other than gzip.
While FIT supports a ramdisk / initrd, no attempt is made to support
this here, since it must be built separately from the Linux build.
Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/20240329032836.141899-3-sjg@chromium.org
Signed-off-by: Will Deacon <will@kernel.org>
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