doc/README.efi

   1 #
   2 # Copyright (C) 2015 Google, Inc
   3 #
   4 # SPDX-License-Identifier:      GPL-2.0+
   5 #
   6
   7 EFI on U-Boot
   8 =============
   9 This document provides information about the implementation of the UEFI API [1]
  10 in U-Boot.
  11
  12
  13 =========== Table of Contents ===========
  14
  15 Motivation
  16 How do I get it?
  17 Status
  18 Future work
  19
  20
  21 Motivation
  22 ----------
  23
  24 With this API support in place, you can run any UEFI payload (such as the Linux
  25 kernel, grub2 or gummiboot) on U-Boot. This dramatically simplifies boot loader
  26 configuration, as U-Boot based systems now look and feel (almost) the same way
  27 as TianoCore based systems.
  28
  29 How do I get it?
  30 ----------------
  31
  32 EFI support for 32bit ARM and AArch64 is already included in U-Boot. All you
  33 need to do is enable
  34
  35   CONFIG_CMD_BOOTEFI=y
  36   CONFIG_EFI_LOADER=y
  37
  38 in your .config file and you will automatically get a bootefi command to run
  39 an efi application as well as snippet in the default distro boot script that
  40 scans for removable media efi binaries as fallback.
  41
  42 Status
  43 ------
  44
  45 I am successfully able to run grub2 and Linux EFI binaries with this code on
  46 ARMv7 as well as AArch64 systems.
  47
  48 When enabled, the resulting U-Boot binary only grows by ~10KB, so it's very
  49 light weight.
  50
  51 All storage devices are directly accessible from the uEFI payload
  52
  53 Removable media booting (search for /efi/boot/boota{a64,arm}.efi) is supported.
  54
  55 Simple use cases like "Plug this SD card into my ARM device and it just
  56 boots into grub which boots into Linux", work very well.
  57
  58
  59 Running HelloWord.efi
  60 ---------------------
  61
  62 You can run a simple 'hello world' EFI program in U-Boot.
  63 Enable the option CONFIG_CMD_BOOTEFI_HELLO.
  64
  65 Then you can boot into U-Boot and type:
  66
  67    > bootefi hello
  68
  69 The 'hello world EFI' program will then run, print a message and exit.
  70
  71
  72 Future work
  73 -----------
  74
  75 Of course, there are still a few things one could do on top:
  76
  77    - Improve disk media detection (don't scan, use what information we
  78 have)
  79    - Add EFI variable support using NVRAM
  80    - Add GFX support
  81    - Make EFI Shell work
  82    - Network device support
  83    - Support for payload exit
  84    - Payload Watchdog support
  85
  86 [1] http://uefi.org/