Tow-Boot

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Because today, I had a thought. https://github.com/u-boot/u-boot/blob/master/board/samsung/smdk5250/Kconfig#L14 If it is a relatively trivial-effort import, this might introduce Exynos support to some capacity.

The main difficulties come not in building U-Boot, but in producing the "user-friendlier" images. E.g. putting the built U-Boot at the right offset, when it's at an offset, and/or installing to the proper storage.

I don't know much about those older Exynos-based chromebooks, so I can't say for sure whether there are gotchas or something else. One thing that would help is some form of documentation detailing how one builds a mainline U-Boot and runs it on their system.

(I'm assuming here it's for the "snow" and "spring" chromebooks you're looking for, other Exynos systems might have different requirements.)

To answer further, let's look at Allwinner stuff.

If you look at the Pine A64-LTS, it's mostly metadata (to build the device page) and some light device-specific information. The most important one is the defconfig

• https://github.com/Tow-Boot/Tow-Boot/blob/2f8fff7be70ebfd22098ee6a351b0075f63955fc/boards/pine64-pineA64LTS/default.nix#L15

When the Tow-Boot infra builds U-Boot here, it "just" builds U-Boot to get the actual build...

... but that's not where the story ends.

If you look under the modules/hardware directory, there is some further "knowledge" about the platform defined:

• https://github.com/Tow-Boot/Tow-Boot/blob/2f8fff7be70ebfd22098ee6a351b0075f63955fc/modules/hardware/allwinner/default.nix

For example, for shared storage, this is where we define where the firmware is written to when building the shared disk image:

• https://github.com/Tow-Boot/Tow-Boot/blob/2f8fff7be70ebfd22098ee6a351b0075f63955fc/modules/hardware/allwinner/default.nix#L71-L75

And this is how we get the right firmware file:

• https://github.com/Tow-Boot/Tow-Boot/blob/2f8fff7be70ebfd22098ee6a351b0075f63955fc/modules/hardware/allwinner/default.nix#L76-L78

And to further close the loop, the platform configuration ends-up resolving the configuration for this:

• https://github.com/Tow-Boot/Tow-Boot/blob/2f8fff7be70ebfd22098ee6a351b0075f63955fc/modules/tow-boot/disk-image.nix#L88

Which is then given to the disk image builder:

• https://github.com/Tow-Boot/Tow-Boot/blob/2f8fff7be70ebfd22098ee6a351b0075f63955fc/modules/tow-boot/disk-image.nix#L59-L61

So really, the difficulties are not in getting U-Boot built, but in wrangling the build results into the right shape. In U-Boot this is generally dependent on the overall platform. Since it is dependent on the platform in U-Boot, it generally means that we need that knowledge written-up for every platform.