Re: [PATCH v9 2/2] arm64: boot: Support Flat Image Tree

[Will Deacon <will@kernel.org>]

On Fri, Dec 01, 2023 at 08:54:42PM -0700, Simon Glass wrote:
> 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. Use
> FIT_COMPRESSION to select a different algorithm.
> 
> The FIT can be examined using 'dumpimage -l'.
> 
> 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. For now there
> is no way to change the compression other than by editing the rule for
> $(obj)/image.fit
> 
> While FIT supports a ramdisk / initrd, no attempt is made to support
> this here, since it must be built separately from the Linux build.
> 
> Signed-off-by: Simon Glass <sjg@chromium.org>
> ---
> 
> Changes in v9:
> - Move the compression control into Makefile.lib
> 
> Changes in v8:
> - Drop compatible string in FDT node
> - Correct sorting of MAINTAINERS to before ARM64 PORT
> - Turn compress part of the make_fit.py comment in to a sentence
> - Add two blank lines before parse_args() and setup_fit()
> - Use 'image.fit: dtbs' instead of BUILD_DTBS var
> - Use '$(<D)/dts' instead of '$(dir $<)dts'
> - Add 'mkimage' details Documentation/process/changes.rst
> - Allow changing the compression used
> - Tweak cover letter since there is only one clean-up patch
> 
> Changes in v7:
> - Add Image as a dependency of image.fit
> - Drop kbuild tag
> - Add dependency on dtbs
> - Drop unnecessary path separator for dtbs
> - Rebase to -next
> 
> Changes in v5:
> - Drop patch previously applied
> - Correct compression rule which was broken in v4
> 
> Changes in v4:
> - Use single quotes for UIMAGE_NAME
> 
> Changes in v3:
> - Drop temporary file image.itk
> - Drop patch 'Use double quotes for image name'
> - Drop double quotes in use of UIMAGE_NAME
> - Drop unnecessary CONFIG_EFI_ZBOOT condition for help
> - Avoid hard-coding "arm64" for the DT architecture
> 
> Changes in v2:
> - Drop patch previously applied
> - Add .gitignore file
> - Move fit rule to Makefile.lib using an intermediate file
> - Drop dependency on CONFIG_EFI_ZBOOT
> - Pick up .dtb files separately from the kernel
> - Correct pylint too-many-args warning for write_kernel()
> - Include the kernel image in the file count
> - Add a pointer to the FIT spec and mention of its wide industry usage
> - Mention the kernel version in the FIT description
> 
>  Documentation/process/changes.rst |   9 +
>  MAINTAINERS                       |   7 +
>  arch/arm64/Makefile               |   7 +-
>  arch/arm64/boot/.gitignore        |   1 +
>  arch/arm64/boot/Makefile          |   6 +-
>  scripts/Makefile.lib              |  16 ++
>  scripts/make_fit.py               | 291 ++++++++++++++++++++++++++++++
>  7 files changed, 334 insertions(+), 3 deletions(-)
>  create mode 100755 scripts/make_fit.py

I'll need Masahiro's Ack on the scripts/ changes before I can take this
one.

Will