RFC: android-style boot image support for flash-kernel

[Roger Shimizu <rosh@debian.org>]

Hi there,

I'm trying to support an ARM based RB3 / DB845c [1] dev-board with
android-style boot image to flash-kernel.
(Surely it's targeting to post-bookworm)

Currently, the dev-board is supported by Linaro [2][3], and most
kernel device-tree, patches and firmware are already upstreamed.
I confirmed that with simple snippet below, generated boot.img can be
used to boot the RB3 / DB845c dev-board with linaro's rootfs [3].
PS. mkbootimg [4] is a tool from android's package to generate
boot.img image to boot the dev-board.

My question is:
- Currently flash-kernel is mainly u-boot based, is it proper to add
"mkbootimg" based devices?
- Does mkbootimg need to support udeb in order to support D-I for this
dev-board in the future?

If this dev-board is feasible, I'm planning to add a few similar
dev-boards from the series.
So your advice will be appreciated!

====
gzip -c9 /boot/vmlinuz-6.1.0-8-arm64 > vmlinuz.gz
cat vmlinuz.gz /usr/lib/linux-image-6.1.0-8-arm64/qcom/sdm845-db845c.dtb > Image
mkbootimg \
    --kernel Image \
    --ramdisk /boot/initrd.img-6.1.0-8-arm64 \
    --output boot.img \
    --pagesize "4096" \
    --base "0x80000000" \
    --kernel_offset "0x8000" \
    --ramdisk_offset "0x1000000" \
    --tags_offset "0x100" \
    --cmdline "root=PARTLABEL=rootfs console=tty0
console=ttyMSM0,115200n8 clk_ignore_unused pd_ignore_unused"
====

[1] https://www.96boards.org/product/rb3-platform/
[2] https://releases.linaro.org/96boards/dragonboard845c/linaro/rescue/latest
[3] https://releases.linaro.org/96boards/dragonboard845c/linaro/debian/latest
[4] https://packages.debian.org/unstable/mkbootimg

Cheers,
Roger