Hello, For FreedomBox, I experimented with building a single UEFI image for multiple arm64 boards as described for SUSE[1]. I tested a single UEFI arm64 image for Rock64, RockPro64 and Raspberry Pi 3B+.
As part this, u-boot will reside on an SPI flash with OS on an eMMC, an SD card, a USB disk or an NVMe drive. Alternatively, u-boot will reside on an SD card with OS on a different drive. We can build these tiny u-boot based firmware images separately or in cases like Raspberry Pi, provide a build script or provide external references on how to get the images. The main OS image will have grub-efi with EFI partition and will not contain u-boot or u-boot boot script. When u-boot starts from SPI flash (or SD card), due to distroboot, it will load the DTB file from /dtb of EFI partition and execute Grub EFI. Grub is responsible for loading the kernel and initrd while DTB is loaded and passed on to the kernel via Grub by u-boot. I had to do two hacks to make this happen: 1) Copy /boot/efi/EFI/debian/grubaa64.efi to /boot/efi/EFI/boot/bootaa64.efi. 2) Copy /usr/lib/linux-image-$(latest)/ to /boot/efi/dtb/. For this I wrote a small kernel hook script. flash-kernel could introduce a new 'mode' of operation, say 'efi-dtb', to help with hack number two. It will have to copy the latest kernel dtbs recursively to /boot/efi/dtb. FreedomBox is currently building an image for each of the boards it supports. Being able to build a single image for all boards of an architecture is a great simplification. Further more, image will contain completely free software even for boards like Raspberry Pi (because non-free firmware need not be shipped by the project). Links: 1) https://www.suse.com/media/article/UEFI%20on%20Top%20of%20U-Boot.pdf Thanks, -- Sunil
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