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Date:   Tue, 5 Dec 2023 12:48:35 +0100
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Subject: Re: [PATCH v9 2/2] arm64: boot: Support Flat Image Tree
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To:     Simon Glass <sjg@chromium.org>,
        linux-arm-kernel@lists.infradead.org
Cc:     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>
References: <20231202035511.487946-1-sjg@chromium.org>
 <20231202035511.487946-3-sjg@chromium.org>
From:   Ahmad Fatoum <a.fatoum@pengutronix.de>
In-Reply-To: <20231202035511.487946-3-sjg@chromium.org>
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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

> +"""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?

> +        fsw.property_u32('load', 0)
> +        fsw.property_u32('entry', 0)

I still think load and entry dummy values are confusing and should be dropped.

> +    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.

Cheers,
Ahmad

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