On December 22th, Alexander Graf of SuSE posted a patch to the U-Boot list, adding EFI payload/application support to U-Boot!

This is my Christmas present for my openSUSE friends :).

U-Boot is a great project for embedded devices. However, convincing everyone involved that only for “a few oddball ARM devices” we need to support different configuration formats from grub2 when all other platforms (PPC, System Z, x86) are standardized on a single format is a nightmare.

So we started to explore alternatives. At first, people tried to get grub2 running using the u-boot api interface. However, FWIW that one doesn’t support relocations, so you need to know where to link grub2 to at compile time. It also seems to be broken more often than not. And on top of it all, it’s a one-off interface, so yet another thing to maintain.

That led to a nifty idea. What if we can just implement the EFI application protocol on top of U-Boot? Then we could compile a single grub2 binary for uEFI based systems and U-Boot based systems and as soon as that one’s loaded, everything looks and feels (almost) the same.

This patch set is the result of pursuing this endeavor.

  – I am successfully able to run grub2 and Linux EFI binaries with this code.
  – When enabled, the resulting U-Boot binary only grows by ~10kb, so it’s very light weight.
  – It works on 32bit ARM and AArch64.
  – All storage devices are directly accessible
  – No runtime services (all calls return unimplemented)
  – No EFI variables

Of course, there are still a few things one could do on top:

  – Implement removable media booting (search for /efi/boot/boota{a64,rm}.efi)
  – Improve disk media detection (don’t scan, use what information we have)
  – Add EFI variable support using NVRAM
  – Add GFX support
  – Make EFI Shell work 😉

But so far, I’m very happy with the state of the patches. They completely eliminate potential arguments against U-Boot internally and give users the chance to run with the same level of comfort on all firmware types.

  disk/part.c: Expose a list of available block drivers
  include/efi_api.h: Add more detailed API definitions
  efi_loader: Add PE image loader
  efi_loader: Add boot time services
  efi_loader: Add console interface
  efi_loader: Add runtime services
  efi_loader: Add disk interfaces
  efi_loader: Add “bootefi” command
  efi_loader: hook up in build environment

More information:
http://lists.denx.de/pipermail/u-boot/2015-December/239054.html

Licensing will be interesting. Tianocore demands BSD, U-Boot prefers GPL.

The first person who gets CHIPSEC to work under this patch, please speak up!