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From:   Simon Glass <sjg@chromium.org>
Date:   Tue, 5 Dec 2023 20:54:41 -0700
Message-ID: <CAPnjgZ3QZh3+2PtmSvje=KAw1n1o_jmhgC1ZnhM9JBoEjLG+fQ@mail.gmail.com>
Subject: Re: [PATCH v9 2/2] arm64: boot: Support Flat Image Tree
To:     Ahmad Fatoum <a.fatoum@pengutronix.de>
Cc:     linux-arm-kernel@lists.infradead.org,
        Masahiro Yamada <masahiroy@kernel.org>,
        U-Boot Mailing List <u-boot@lists.denx.de>,
        Nicolas Schier <nicolas@fjasle.eu>,
        Tom Rini <trini@konsulko.com>,
        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,
        Pengutronix Kernel Team <kernel@pengutronix.de>
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Hi Ahmad,

On Tue, 5 Dec 2023 at 04:48, Ahmad Fatoum <a.fatoum@pengutronix.de> wrote:
>
> Hello Simon,
>
> On 02.12.23 04:54, 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>
>
> kernel_noload support is now in barebox next branch and I tested this
> series against it:
>
> Tested-by: Ahmad Fatoum <a.fatoum@pengutronix.de> # barebox
>

OK great thank you.

> > +"""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/image.itk
> > +        /tmp/kern/arch/arm64/boot/dts/ -E -c gzip
> > +
> > +Creates a FIT containing the supplied kernel and a directory containing the
> > +devicetree files.
> > +
> > +Use -E to generate an external FIT (where the data is placed after the
> > +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, such
> > +as U-Boot, Linuxboot, Tianocore, etc.
>
> Feel free to add barebox to the list. Did you check whether Linuxboot and
> Tianocore support kernel_noload?

Only what I was told by people in those projects. They may not even
look at the load address, but I am not an expert on that.

>
> > +        fsw.property_u32('load', 0)
> > +        fsw.property_u32('entry', 0)
>
> I still think load and entry dummy values are confusing and should be dropped.

This is what the spec requires at present. But I agree we should
change it. I will dig into that at some point to see what is needed.

>
> > +    with fsw.add_node(f'fdt-{seq}'):
> > +        # Get the compatible / model information
> > +        with open(fname, 'rb') as inf:
> > +            data = inf.read()
> > +        fdt = libfdt.FdtRo(data)
> > +        model = fdt.getprop(0, 'model').as_str()
> > +        compat = 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 = compress_data(inf, compress)
> > +        fsw.property('data', compressed)
> > +    return model, compat
>
> After Doug's elaboration, extracting multiple compatibles is fine by me.

OK good.

Regards,
Simon