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Date: Tue, 9 Jan 2024 09:33:49 -0500
From: Tom Rini <trini@konsulko.com>
To: Masahiro Yamada <masahiroy@kernel.org>
Cc: Simon Glass <sjg@chromium.org>, Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	Ahmad Fatoum <a.fatoum@pengutronix.de>,
	U-Boot Mailing List <u-boot@lists.denx.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>, linux-doc@vger.kernel.org,
	linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
	workflows@vger.kernel.org, Rob Herring <robh@kernel.org>
Subject: Re: [PATCH v9 2/2] arm64: boot: Support Flat Image Tree
Message-ID: <20240109143349.GR1610741@bill-the-cat>
References: <20231202035511.487946-1-sjg@chromium.org>
 <20231202035511.487946-3-sjg@chromium.org>
 <20231213121353.GA31326@willie-the-truck>
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On Tue, Jan 09, 2024 at 11:01:42PM +0900, Masahiro Yamada wrote:
> Hi Simon,
>=20
>=20
> On Wed, Jan 3, 2024 at 8:47=E2=80=AFAM Simon Glass <sjg@chromium.org> wro=
te:
> >
> > Hi Masahiro,
> >
> > On Wed, Dec 13, 2023 at 5:14=E2=80=AFAM Will Deacon <will@kernel.org> w=
rote:
> > >
> > > 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. Suppor=
ted
> > > > compression options are the same as the Image.xxx files. For now th=
ere
> > > > 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 us=
age
> > > > - 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 th=
is
> > > one.
> >
> > Any thoughts on this request, please?
> >
> > Regards,
> > Simon
> >
>=20
>=20
>=20
> As I mentioned before, I am concerned with having
> the same "compatible" entries, with different contents,
> as you use the "compatible" string as an ID to selecting
> the target config node, right?
>=20
>=20
>=20
>=20
>=20
> $ fdtdump  arch/arm64/boot/image.fit
>=20
>         ...
>=20
>         conf-10 {
>             compatible =3D "tq,am642-tqma6442l-mbax4xxl",
> "tq,am642-tqma6442l", "ti,am642";
>             description =3D "TQ-Systems TQMa64xxL SoM on MBax4xxL carrier=
 board";
>             fdt =3D "fdt-10";
>             kernel =3D "kernel";
>         };
>=20
>         ...
>=20
>         conf-25 {
>             compatible =3D "tq,am642-tqma6442l-mbax4xxl",
> "tq,am642-tqma6442l", "ti,am642";
>             description =3D "TQ-Systems TQMa64xxL SoM on MBax4xxL carrier=
 board";
>             fdt =3D "fdt-25";
>             kernel =3D "kernel";
>         };

I had asked Rob a while ago about if having the same compatible for two
functionally different machines is a feature, or a bug, and I don't
think either of us fully agreed either way. I'd be leaning towards
saying the above example is a bug in the dts files, it's just not been a
bug people have worried about before due to (sadly) how little the
top-level compatible has been used.

--=20
Tom
>=20
>=20
>=20
>=20
>=20
>=20
>=20
>=20
>=20
>=20
>=20
>=20
> --=20
> Best Regards
> Masahiro Yamada

--=20
Tom

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