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From: Simon Glass <sjg@chromium.org>
Date: Fri, 8 Mar 2024 16:50:34 +1300
Message-ID: <CAFLszTiDi4N7NbVx6BH8M1ccGu9MNAokQuo_DyGtzH7qrrdiPA@mail.gmail.com>
Subject: Re: [PATCH v10 2/2] arm64: boot: Support Flat Image Tree
To: Masahiro Yamada <masahiroy@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org, 
	Ahmad Fatoum <a.fatoum@pengutronix.de>, Nicolas Schier <nicolas@fjasle.eu>, 
	Catalin Marinas <catalin.marinas@arm.com>, Jonathan Corbet <corbet@lwn.net>, 
	Nathan Chancellor <nathan@kernel.org>, Nick Terrell <terrelln@fb.com>, Will Deacon <will@kernel.org>, 
	linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org, 
	linux-kernel@vger.kernel.org, workflows@vger.kernel.org
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Hi Masahiro,

On Sun, 25 Feb 2024 at 21:41, Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Wed, Feb 21, 2024 at 9:37=E2=80=AFPM Masahiro Yamada <masahiroy@kernel=
org> wrote:
> >
> > On Sat, Feb 3, 2024 at 2:30=E2=80=AFAM Simon Glass <sjg@chromium.org> w=
rote:
> > >
> > > 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, ignorin=
g
> > > the overlay .dtbo files.
> > >
> > > This features requires pylibfdt (use 'pip install libfdt'). It also
> > > requires compression utilities for the algorithm being used. Supporte=
d
> > > 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>
> > > ---
> > >
> > > Changes in v10:
> > > - Make use of dtbs-list file
> > > - Mention dtbs-list and FIT_COMPRESSION
> > > - Update copyright year
> > > - Update cover letter to take account of an applied patch
> > >
> > > 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 usag=
e
> > > - 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               | 298 ++++++++++++++++++++++++++++=
++
> > >  7 files changed, 341 insertions(+), 3 deletions(-)
> > >  create mode 100755 scripts/make_fit.py
> > >
> > > diff --git a/Documentation/process/changes.rst b/Documentation/proces=
s/changes.rst
> > > index 50b3d1cb1115..a8110965e4e1 100644
> > > --- a/Documentation/process/changes.rst
> > > +++ b/Documentation/process/changes.rst
> > > @@ -62,6 +62,7 @@ Sphinx\ [#f1]_         2.4.4            sphinx-buil=
d --version
> > >  cpio                   any              cpio --version
> > >  GNU tar                1.28             tar --version
> > >  gtags (optional)       6.6.5            gtags --version
> > > +mkimage (optional)     2017.01          mkimage --version
> > >  =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D  =3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D
> > >
> > >  .. [#f1] Sphinx is needed only to build the Kernel documentation
> > > @@ -189,6 +190,14 @@ The kernel build requires GNU GLOBAL version 6.6=
5 or later to generate
> > >  tag files through ``make gtags``.  This is due to its use of the gta=
gs
> > >  ``-C (--directory)`` flag.
> > >
> > > +mkimage
> > > +-------
> > > +
> > > +This tool is used when building a Flat Image Tree (FIT), commonly us=
ed on ARM
> > > +platforms. The tool is available via the ``u-boot-tools`` package or=
 can be
> > > +built from the U-Boot source code. See the instructions at
> > > +https://docs.u-boot.org/en/latest/build/tools.html#building-tools-fo=
r-linux
> > > +
> > >  System utilities
> > >  ****************
> > >
> > > diff --git a/MAINTAINERS b/MAINTAINERS
> > > index 61117c3afa80..10c2753d7bcc 100644
> > > --- a/MAINTAINERS
> > > +++ b/MAINTAINERS
> > > @@ -3026,6 +3026,13 @@ F:       drivers/mmc/host/sdhci-of-arasan.c
> > >  N:     zynq
> > >  N:     xilinx
> > >
> > > +ARM64 FIT SUPPORT
> > > +M:     Simon Glass <sjg@chromium.org>
> > > +L:     linux-arm-kernel@lists.infradead.org (moderated for non-subsc=
ribers)
> > > +S:     Maintained
> > > +F:     arch/arm64/boot/Makefile
> > > +F:     scripts/make_fit.py
> > > +
> > >  ARM64 PORT (AARCH64 ARCHITECTURE)
> > >  M:     Catalin Marinas <catalin.marinas@arm.com>
> > >  M:     Will Deacon <will@kernel.org>
> > > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> > > index 83cd2b7234b9..5de2b02f549a 100644
> > > --- a/arch/arm64/Makefile
> > > +++ b/arch/arm64/Makefile
> > > @@ -150,7 +150,7 @@ libs-$(CONFIG_EFI_STUB) +=3D $(objtree)/drivers/f=
irmware/efi/libstub/lib.a
> > >  # Default target when executing plain make
> > >  boot           :=3D arch/arm64/boot
> > >
> > > -BOOT_TARGETS   :=3D Image vmlinuz.efi
> > > +BOOT_TARGETS   :=3D Image vmlinuz.efi image.fit
> > >
> > >  PHONY +=3D $(BOOT_TARGETS)
> > >
> > > @@ -162,7 +162,9 @@ endif
> > >
> > >  all:   $(notdir $(KBUILD_IMAGE))
> > >
> > > -vmlinuz.efi: Image
> > > +image.fit: dtbs
> > > +
> > > +vmlinuz.efi image.fit: Image
> > >  $(BOOT_TARGETS): vmlinux
> > >         $(Q)$(MAKE) $(build)=3D$(boot) $(boot)/$@
> > >
> > > @@ -215,6 +217,7 @@ virtconfig:
> > >  define archhelp
> > >    echo  '* Image.gz      - Compressed kernel image (arch/$(ARCH)/boo=
t/Image.gz)'
> > >    echo  '  Image         - Uncompressed kernel image (arch/$(ARCH)/b=
oot/Image)'
> > > +  echo  '  image.fit     - Flat Image Tree (arch/$(ARCH)/boot/image.=
fit)'
> > >    echo  '  install       - Install uncompressed kernel'
> > >    echo  '  zinstall      - Install compressed kernel'
> > >    echo  '                  Install using (your) ~/bin/installkernel =
or'
> > > diff --git a/arch/arm64/boot/.gitignore b/arch/arm64/boot/.gitignore
> > > index af5dc61f8b43..abaae9de1bdd 100644
> > > --- a/arch/arm64/boot/.gitignore
> > > +++ b/arch/arm64/boot/.gitignore
> > > @@ -2,3 +2,4 @@
> > >  Image
> > >  Image.gz
> > >  vmlinuz*
> > > +image.fit
> > > diff --git a/arch/arm64/boot/Makefile b/arch/arm64/boot/Makefile
> > > index a5a787371117..ab21af82913e 100644
> > > --- a/arch/arm64/boot/Makefile
> > > +++ b/arch/arm64/boot/Makefile
> > > @@ -16,7 +16,8 @@
> > >
> > >  OBJCOPYFLAGS_Image :=3D-O binary -R .note -R .note.gnu.build-id -R .=
comment -S
> > >
> > > -targets :=3D Image Image.bz2 Image.gz Image.lz4 Image.lzma Image.lzo=
 Image.zst
> > > +targets :=3D Image Image.bz2 Image.gz Image.lz4 Image.lzma Image.lzo=
 \
> > > +       Image.zst image.fit
> > >
> > >  $(obj)/Image: vmlinux FORCE
> > >         $(call if_changed,objcopy)
> > > @@ -39,6 +40,9 @@ $(obj)/Image.lzo: $(obj)/Image FORCE
> > >  $(obj)/Image.zst: $(obj)/Image FORCE
> > >         $(call if_changed,zstd)
> > >
> > > +$(obj)/image.fit: $(obj)/Image FORCE
> > > +       $(call cmd,fit)
> >
> >
> >
> > The point for using dtbs-list is
> > to avoid rebuilding image.fit needlessly.
> >
> >
> > This should be:
> >
> > $(obj)/image.fit: $(obj)/Image $(obj)/dts/dtbs-list FORCE
> >         $(call if_changed,fit)
> >
> >
> >
> >
> >
> > > +
> > >  EFI_ZBOOT_PAYLOAD      :=3D Image
> > >  EFI_ZBOOT_BFD_TARGET   :=3D elf64-littleaarch64
> > >  EFI_ZBOOT_MACH_TYPE    :=3D ARM64
> > > diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> > > index b35d39022a30..4efb5ad07fd7 100644
> > > --- a/scripts/Makefile.lib
> > > +++ b/scripts/Makefile.lib
> > > @@ -502,6 +502,22 @@ quiet_cmd_uimage =3D UIMAGE  $@
> > >                         -a $(UIMAGE_LOADADDR) -e $(UIMAGE_ENTRYADDR) =
\
> > >                         -n '$(UIMAGE_NAME)' -d $< $@
> > >
> > > +# Flat Image Tree (FIT)
> > > +# This allows for packaging of a kernel and all devicetrees files, u=
sing
> > > +# compression.
> > > +# ------------------------------------------------------------------=
---------
> > > +
> > > +MAKE_FIT :=3D $(srctree)/scripts/make_fit.py
> > > +
> > > +# Use this to override the compression algorithm
> > > +FIT_COMPRESSION ?=3D gzip
> > > +
> > > +quiet_cmd_fit =3D FIT     $@
> > > +      cmd_fit =3D $(MAKE_FIT) -f $@ --arch $(UIMAGE_ARCH) --os linux=
 \
> > > +                       --name '$(UIMAGE_NAME)' \
> > > +                       --compress $(FIT_COMPRESSION) -k $< \
> > > +                       @arch/$(SRCARCH)/boot/dts/dtbs-list
> >
> >
> >
> >
> > cmd_fit =3D $(MAKE_FIT) -f $@ --arch $(UIMAGE_ARCH) --os linux \
> >                 --name '$(UIMAGE_NAME)' \
> >                 --compress $(FIT_COMPRESSION) -k $< @$(word 2,$^)
> >
> >
> >
> >
> >
> > > +
> > >  # XZ
> > >  # ------------------------------------------------------------------=
---------
> > >  # Use xzkern to compress the kernel image and xzmisc to compress oth=
er things.
> > > diff --git a/scripts/make_fit.py b/scripts/make_fit.py
> > > new file mode 100755
> > > index 000000000000..69eee32960ae
> > > --- /dev/null
> > > +++ b/scripts/make_fit.py
> > > @@ -0,0 +1,298 @@
> > > +#!/usr/bin/env python3
> > > +# SPDX-License-Identifier: GPL-2.0+
> > > +#
> > > +# Copyright 2024 Google LLC
> > > +# Written by Simon Glass <sjg@chromium.org>
> > > +#
> > > +
> > > +"""Build a FIT containing a lot of devicetree files
> > > +
> > > +Usage:
> > > +    make_fit.py -A arm64 -n 'Linux-6.6' -O linux
> > > +        -f arch/arm64/boot/image.fit -k /tmp/kern/arch/arm64/boot/im=
age.itk
> > > +        @arch/arm64/boot/dts/dtbs-list -E -c gzip
> > > +
> > > +Creates a FIT containing the supplied kernel and a set of devicetree=
 files,
> > > +either specified individually or listed in a file (with an '@' prefi=
x). Files
> > > +which don't end in '.dtb' are silently ignored.
> >
> >
> > Why do you need to check the suffix?
> >
> >
> >
> > > +
> > > +Use -E to generate an external FIT (where the data is placed after t=
he
> > > +FIT data structure). This allows parsing of the data without loading
> > > +the entire FIT.
> > > +
> > > +Use -c to compress the data, using bzip2, gzip, lz4, lzma, lzo and
> > > +zstd algorithms.
> > > +
> > > +The resulting FIT can be booted by bootloaders which support FIT, su=
ch
> > > +as U-Boot, Linuxboot, Tianocore, etc.
> > > +
> > > +Note that this tool does not yet support adding a ramdisk / initrd.
> > > +"""
> > > +
> > > +import argparse
> > > +import collections
> > > +import os
> > > +import subprocess
> > > +import sys
> > > +import tempfile
> > > +import time
> > > +
> > > +import libfdt
> > > +
> > > +
> > > +# Tool extension and the name of the command-line tools
> > > +CompTool =3D collections.namedtuple('CompTool', 'ext,tools')
> > > +
> > > +COMP_TOOLS =3D {
> > > +    'bzip2': CompTool('.bz2', 'bzip2'),
> > > +    'gzip': CompTool('.gz', 'pigz,gzip'),
> > > +    'lz4': CompTool('.lz4', 'lz4'),
> > > +    'lzma': CompTool('.lzma', 'lzma'),
> > > +    'lzo': CompTool('.lzo', 'lzop'),
> > > +    'zstd': CompTool('.zstd', 'zstd'),
> > > +}
> > > +
> > > +
> > > +def parse_args():
> > > +    """Parse the program ArgumentParser
> > > +
> > > +    Returns:
> > > +        Namespace object containing the arguments
> > > +    """
> > > +    epilog =3D 'Build a FIT from a directory tree containing .dtb fi=
les'
> > > +    parser =3D argparse.ArgumentParser(epilog=3Depilog)
> > > +    parser.add_argument('-A', '--arch', type=3Dstr, required=3DTrue,
> > > +          help=3D'Specifies the architecture')
> > > +    parser.add_argument('-c', '--compress', type=3Dstr, default=3D'n=
one',
> > > +          help=3D'Specifies the compression')
> > > +    parser.add_argument('-E', '--external', action=3D'store_true',
> > > +          help=3D'Convert the FIT to use external data')
> > > +    parser.add_argument('-n', '--name', type=3Dstr, required=3DTrue,
> > > +          help=3D'Specifies the name')
> > > +    parser.add_argument('-O', '--os', type=3Dstr, required=3DTrue,
> > > +          help=3D'Specifies the operating system')
> > > +    parser.add_argument('-f', '--fit', type=3Dstr, required=3DTrue,
> > > +          help=3D'Specifies the output file (.fit)')
> >
> >
> >
> > I like -o (--output) to specify the output file.
> >
> >
> >
> >     parser.add_argument('-o', '--output', type=3Dstr, required=3DTrue,
> >              help=3D'Specifies the output file (.fit)')
> >
> >
> >
> >
> >
> > > +    parser.add_argument('-k', '--kernel', type=3Dstr, required=3DTru=
e,
> > > +          help=3D'Specifies the (uncompressed) kernel input file (.i=
tk)')
> > > +    parser.add_argument('srcdir', type=3Dstr, nargs=3D'*',
> > > +          help=3D'Specifies the directory tree that contains .dtb fi=
les')
> >
> >
> > srcdir?
> >
> > You changed the positional parameters to take dtb files.
> >
> >
> >
> >
> >
> >
> > > +
> > > +    return parser.parse_args()
> > > +
> > > +
> > > +def setup_fit(fsw, name):
> > > +    """Make a start on writing the FIT
> > > +
> > > +    Outputs the root properties and the 'images' node
> > > +
> > > +    Args:
> > > +        fsw (libfdt.FdtSw): Object to use for writing
> > > +        name (str): Name of kernel image
> > > +    """
> > > +    fsw.INC_SIZE =3D 65536
> > > +    fsw.finish_reservemap()
> > > +    fsw.begin_node('')
> > > +    fsw.property_string('description', f'{name} with devicetree set'=
)
> > > +    fsw.property_u32('#address-cells', 1)
> > > +
> > > +    fsw.property_u32('timestamp', int(time.time()))
> > > +    fsw.begin_node('images')
> > > +
> > > +
> > > +def write_kernel(fsw, data, args):
> > > +    """Write out the kernel image
> > > +
> > > +    Writes a kernel node along with the required properties
> > > +
> > > +    Args:
> > > +        fsw (libfdt.FdtSw): Object to use for writing
> > > +        data (bytes): Data to write (possibly compressed)
> > > +        args (Namespace): Contains necessary strings:
> > > +            arch: FIT architecture, e.g. 'arm64'
> > > +            fit_os: Operating Systems, e.g. 'linux'
> > > +            name: Name of OS, e.g. 'Linux-6.6.0-rc7'
> > > +            compress: Compression algorithm to use, e.g. 'gzip'
> > > +    """
> > > +    with fsw.add_node('kernel'):
> > > +        fsw.property_string('description', args.name)
> > > +        fsw.property_string('type', 'kernel_noload')
> > > +        fsw.property_string('arch', args.arch)
> > > +        fsw.property_string('os', args.os)
> > > +        fsw.property_string('compression', args.compress)
> > > +        fsw.property('data', data)
> > > +        fsw.property_u32('load', 0)
> > > +        fsw.property_u32('entry', 0)
> > > +
> > > +
> > > +def finish_fit(fsw, entries):
> > > +    """Finish the FIT ready for use
> > > +
> > > +    Writes the /configurations node and subnodes
> > > +
> > > +    Args:
> > > +        fsw (libfdt.FdtSw): Object to use for writing
> > > +        entries (list of tuple): List of configurations:
> > > +            str: Description of model
> > > +            str: Compatible stringlist
> > > +    """
> > > +    fsw.end_node()
> > > +    seq =3D 0
> > > +    with fsw.add_node('configurations'):
> > > +        for model, compat in entries:
> > > +            seq +=3D 1
> > > +            with fsw.add_node(f'conf-{seq}'):
> > > +                fsw.property('compatible', bytes(compat))
> > > +                fsw.property_string('description', model)
> > > +                fsw.property_string('fdt', f'fdt-{seq}')
> > > +                fsw.property_string('kernel', 'kernel')
> > > +    fsw.end_node()
> > > +
> > > +
> > > +def compress_data(inf, compress):
> > > +    """Compress data using a selected algorithm
> > > +
> > > +    Args:
> > > +        inf (IOBase): Filename containing the data to compress
> > > +        compress (str): Compression algorithm, e.g. 'gzip'
> > > +
> > > +    Return:
> > > +        bytes: Compressed data
> > > +    """
> > > +    if compress =3D=3D 'none':
> > > +        return inf.read()
> > > +
> > > +    comp =3D COMP_TOOLS.get(compress)
> > > +    if not comp:
> > > +        raise ValueError(f"Unknown compression algorithm '{compress}=
'")
> > > +
> > > +    with tempfile.NamedTemporaryFile() as comp_fname:
> > > +        with open(comp_fname.name, 'wb') as outf:
> > > +            done =3D False
> > > +            for tool in comp.tools.split(','):
> > > +                try:
> > > +                    subprocess.call([tool, '-c'], stdin=3Dinf, stdou=
t=3Doutf)
> > > +                    done =3D True
> > > +                    break
> > > +                except FileNotFoundError:
> > > +                    pass
> > > +            if not done:
> > > +                raise ValueError(f'Missing tool(s): {comp.tools}\n')
> > > +            with open(comp_fname.name, 'rb') as compf:
> > > +                comp_data =3D compf.read()
> > > +    return comp_data
> > > +
> > > +
> > > +def output_dtb(fsw, seq, fname, arch, compress):
> > > +    """Write out a single devicetree to the FIT
> > > +
> > > +    Args:
> > > +        fsw (libfdt.FdtSw): Object to use for writing
> > > +        seq (int): Sequence number (1 for first)
> > > +        fmame (str): Filename containing the DTB
> > > +        arch: FIT architecture, e.g. 'arm64'
> > > +        compress (str): Compressed algorithm, e.g. 'gzip'
> > > +
> > > +    Returns:
> > > +        tuple:
> > > +            str: Model name
> > > +            bytes: Compatible stringlist
> > > +    """
> > > +    with fsw.add_node(f'fdt-{seq}'):
> > > +        # Get the compatible / model information
> > > +        with open(fname, 'rb') as inf:
> > > +            data =3D inf.read()
> > > +        fdt =3D libfdt.FdtRo(data)
> > > +        model =3D fdt.getprop(0, 'model').as_str()
> > > +        compat =3D fdt.getprop(0, 'compatible')
> > > +
> > > +        fsw.property_string('description', model)
> > > +        fsw.property_string('type', 'flat_dt')
> > > +        fsw.property_string('arch', arch)
> > > +        fsw.property_string('compression', compress)
> > > +        fsw.property('compatible', bytes(compat))
> > > +
> > > +        with open(fname, 'rb') as inf:
> > > +            compressed =3D compress_data(inf, compress)
> > > +        fsw.property('data', compressed)
> > > +    return model, compat
> > > +
> > > +
> > > +def build_fit(args):
> > > +    """Build the FIT from the provided files and arguments
> > > +
> > > +    Args:
> > > +        args (Namespace): Program arguments
> > > +
> > > +    Returns:
> > > +        tuple:
> > > +            bytes: FIT data
> > > +            int: Number of configurations generated
> > > +            size: Total uncompressed size of data
> > > +    """
> > > +    def add_file(fname):
> > > +        nonlocal seq, size
> > > +
> > > +        if os.path.splitext(fname)[1] =3D=3D '.dtb':
> > > +            seq +=3D 1
> > > +            size +=3D os.path.getsize(fname)
> > > +            model, compat =3D output_dtb(fsw, seq, fname, args.arch,
> > > +                                       args.compress)
> > > +            entries.append([model, compat])
> > > +            return True
> > > +
> > > +    seq =3D 0
> > > +    size =3D 0
> > > +    fsw =3D libfdt.FdtSw()
> > > +    setup_fit(fsw, args.name)
> > > +    entries =3D []
> > > +
> > > +    # Handle the kernel
> > > +    with open(args.kernel, 'rb') as inf:
> > > +        comp_data =3D compress_data(inf, args.compress)
> > > +    size +=3D os.path.getsize(args.kernel)
> > > +    write_kernel(fsw, comp_data, args)
> > > +
> > > +    for path in args.srcdir:
> > > +        # Handle a list of devicetree files
> > > +        if path.startswith('@'):
> > > +            with open(path[1:], 'r', encoding=3D'utf-8') as inf:
> > > +                for fname in inf.read().splitlines():
> > > +                    add_file(fname)
> >
> >
> >
> >
> > You missed the point of my suggestion.
> >
> >
> > I did not mean the "@file" syntax
> > specifically for containing the device trees.
> >
> >
> > It is common for tools to support the "@file" syntax
> > to avoid "Argument list too long" error.
> >
> >
> >
> > See "man ar", "man ld", etc. for example.
> >
> >
> >  @file
> >    Read command=E2=80=90line options from file. The options read are in=
serted in
> >    place of the original @file option. If file does not exist, or canno=
t
> >    be read, then the option will be treated literally, and not removed.
> >
> >
> >
> >
> > It must be generic enough to contain any command line parameters.
> >
> >
> > And, you do not even implement it yourself because
> > it is just a matter of adding fromfile_prefix_chars=3D'@'
> >
> >
> > See the document.
> >
> >   https://docs.python.org/3/library/argparse.html#fromfile-prefix-chars
>
>
>
>
>
> Or, if you prefer using the 'file' only for containing DTB files,
> I think it is better to use a standard short/long option instead of
> the @file syntax.
>
>
> For example, 'tar' can take files from FILE instead of the
> positional parameters of the command line.
>
>
> 'man tar':
>
>   -T, --files-from=3DFILE
>        Get names to extract or create from FILE.

No, I am fine with the @ thing. I didn't know it was built into argparse

Regards,
Simon