u-boot/doc/README.efi

9   1  U-Boot on EFI
23   2  EFI on U-Boot
29 U-Boot on EFI
31 This document provides information about U-Boot running on top of EFI, either
32 as an application or just as a means of getting U-Boot onto a new platform.
39 - You have EFI running on a board but U-Boot does not natively support it
40 fully yet. You can boot into U-Boot from EFI and use that until U-Boot is
46 - You plan to use coreboot to boot into U-Boot but coreboot support does
47 not currently exist for your platform. In the meantime you can use U-Boot
48 on EFI and then move to U-Boot on coreboot when ready
50 - You use EFI but want to experiment with a simpler alternative like U-Boot
59 U-Boot supports running as an EFI application for 32-bit EFI only. This is
63 More usefully, U-Boot supports building itself as a payload for either 32-bit
64 or 64-bit EFI. U-Boot is packaged up and loaded in its entirety by EFI. Once
65 started, U-Boot changes to 32-bit mode (currently) and takes over the
66 machine. You can use devices, boot a kernel, etc.
75 To build U-Boot as an EFI application (32-bit EFI required), enable CONFIG_EFI
77 Just build U-Boot as normal, e.g.
82 To build U-Boot as an EFI payload (32-bit or 64-bit EFI can be used), adjust an
85 boolean Kconfig options. Then build U-Boot as normal, e.g.
92    u-boot-app.efi      - U-Boot EFI application
93    u-boot-payload.efi  - U-Boot EFI payload application
103    cp /path/to/u-boot*.efi /tmp/efi
107 type 'fs0:u-boot-payload.efi' to run the payload or 'fs0:u-boot-app.efi' to
111 To try it on real hardware, put u-boot-app.efi on a suitable boot medium,
114    fs0:u-boot-payload.efi
116 (or fs0:u-boot-app.efi for the application)
118 This will start the payload, copy U-Boot into RAM and start U-Boot. Note
134 For the application the whole of U-Boot is built as a shared library. The
136 functions with efi_init(), sets up U-Boot global_data, allocates memory for
137 U-Boot's malloc(), etc. and enters the normal init sequence (board_init_f()
140 Since U-Boot limits its memory access to the allocated regions very little
146 'boot services' to send and receive characters. Although it is implemented
148 boot EFI with video output then the 'serial' device will operate on your
151 consoles will be active. Even though U-Boot does the same thing normally,
152 These are features of EFI, not U-Boot.
155 U-Boot is highly portable. Most of the difficulty is in modifying the
166 U-Boot exactly as normal for your target board, then adding the entire
172 function is called by EFI. It is responsible for copying U-Boot from its
173 original location into memory, disabling EFI boot services and starting
174 U-Boot. U-Boot then starts as normal, relocates, starts all drivers, etc.
180 used by U-Boot (the payload). In fact when U-Boot starts it has all of the
186 The payload can pass information to U-Boot in the form of EFI tables. At
189 display this list. U-Boot uses the list to work out where to relocate
192 Although U-Boot can use any memory it likes, EFI marks some memory as used
193 by 'run-time services', code that hangs around while U-Boot is running and
196 fan speed. U-Boot uses only 'conventional' memory, in EFI terminology. It
202 U-Boot drivers typically don't use interrupts. Since EFI enables interrupts
203 it is possible that an interrupt will fire that U-Boot cannot handle. This
204 seems to cause problems. For this reason the U-Boot payload runs with
215 Everything else is built as a normal U-Boot, so is always 32-bit on x86 at
237 - Avoid turning off boot services in the stub. Instead allow U-Boot to make
238 use of boot services in case it wants to. It is unclear what it might want
269 EFI on U-Boot
272 In addition to support for running U-Boot as a UEFI application, U-Boot itself
280 kernel, grub2 or gummiboot) on U-Boot. This dramatically simplifies boot loader
281 configuration, as U-Boot based systems now look and feel (almost) the same way
287 EFI support for 32bit ARM and AArch64 is already included in U-Boot. All you
294 an efi application as well as snippet in the default distro boot script that
303 When enabled, the resulting U-Boot binary only grows by ~10KB, so it's very
308 Removable media booting (search for /efi/boot/boota{a64,arm}.efi) is supported.
317 You can run a simple 'hello world' EFI program in U-Boot.
320 Then you can boot into U-Boot and type: