Re: [PATCH v7 2/2] arm64: boot: Support Flat Image Tree

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 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 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

 MAINTAINERS                |   7 +
 arch/arm64/Makefile        |   9 +-
 arch/arm64/boot/.gitignore |   1 +
 arch/arm64/boot/Makefile   |   6 +-
 scripts/Makefile.lib       |  13 ++
 scripts/make_fit.py        | 289 +++++++++++++++++++++++++++++++++++++
 6 files changed, 322 insertions(+), 3 deletions(-)
 create mode 100755 scripts/make_fit.py

diff --git a/MAINTAINERS b/MAINTAINERS
index 14587be87a33..d609f0e8deb3 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS

@@ -1585,6 +1585,13 @@ F:       Documentation/process/maintainer-soc*.rst
 F:     arch/arm/boot/dts/Makefile
 F:     arch/arm64/boot/dts/Makefile

+ARM64 FIT SUPPORT
+M:     Simon Glass <sjg@chromium.org>
+L:     linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)
+S:     Maintained
+F:     arch/arm64/boot/Makefile
+F:     scripts/make_fit.py
+
 ARM ARCHITECTED TIMER DRIVER
 M:     Mark Rutland <mark.rutland@arm.com>
 M:     Marc Zyngier <maz@kernel.org>

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 1bd4fae6e806..18e092de7cdb 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile

@@ -36,6 +36,8 @@ ifeq ($(CONFIG_BROKEN_GAS_INST),y)
 $(warning Detected assembler with broken .inst; disassembly will be unreliable)
 endif

+KBUILD_DTBS      := dtbs

 $(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,gzip)