# SPDX-License-Identifier: GPL-2.0+
#
-=========== Table of Contents ===========
-
- 1 U-Boot on EFI
- 1.1 In God's Name, Why?
- 1.2 Status
- 1.3 Build Instructions
- 1.4 Trying it out
- 1.5 Inner workings
- 1.6 EFI Application
- 1.7 EFI Payload
- 1.8 Tables
- 1.9 Interrupts
- 1.10 32/64-bit
- 1.11 Future work
- 1.12 Where is the code?
-
- 2 EFI on U-Boot
- 2.1 In God's Name, Why?
- 2.2 How do I get it?
- 2.3 Status
- 2.4 Future work
-
-U-Boot on EFI
+EFI on U-Boot
=============
-This document provides information about U-Boot running on top of EFI, either
-as an application or just as a means of getting U-Boot onto a new platform.
-
-
-In God's Name, Why?
--------------------
-This is useful in several situations:
-
-- You have EFI running on a board but U-Boot does not natively support it
-fully yet. You can boot into U-Boot from EFI and use that until U-Boot is
-fully ported
-
-- You need to use an EFI implementation (e.g. UEFI) because your vendor
-requires it in order to provide support
+This document provides information about the implementation of the UEFI API [1]
+in U-Boot.
-- You plan to use coreboot to boot into U-Boot but coreboot support does
-not currently exist for your platform. In the meantime you can use U-Boot
-on EFI and then move to U-Boot on coreboot when ready
-
-- You use EFI but want to experiment with a simpler alternative like U-Boot
+=========== Table of Contents ===========
+Motivation
+How do I get it?
Status
-------
-Only x86 is supported at present. If you are using EFI on another architecture
-you may want to reconsider. However, much of the code is generic so could be
-ported.
-
-U-Boot supports running as an EFI application for 32-bit EFI only. This is
-not very useful since only a serial port is provided. You can look around at
-memory and type 'help' but that is about it.
-
-More usefully, U-Boot supports building itself as a payload for either 32-bit
-or 64-bit EFI. U-Boot is packaged up and loaded in its entirety by EFI. Once
-started, U-Boot changes to 32-bit mode (currently) and takes over the
-machine. You can use devices, boot a kernel, etc.
-
-
-Build Instructions
-------------------
-First choose a board that has EFI support and obtain an EFI implementation
-for that board. It will be either 32-bit or 64-bit. Alternatively, you can
-opt for using QEMU [1] and the OVMF [2], as detailed below.
-
-To build U-Boot as an EFI application (32-bit EFI required), enable CONFIG_EFI
-and CONFIG_EFI_APP. The efi-x86 config (efi-x86_defconfig) is set up for this.
-Just build U-Boot as normal, e.g.
-
- make efi-x86_defconfig
- make
-
-To build U-Boot as an EFI payload (32-bit or 64-bit EFI can be used), adjust an
-existing config (like qemu-x86_defconfig) to enable CONFIG_EFI, CONFIG_EFI_STUB
-and either CONFIG_EFI_STUB_32BIT or CONFIG_EFI_STUB_64BIT. All of these are
-boolean Kconfig options. Then build U-Boot as normal, e.g.
-
- make qemu-x86_defconfig
- make
-
-You will end up with one of these files depending on what you build for:
-
- u-boot-app.efi - U-Boot EFI application
- u-boot-payload.efi - U-Boot EFI payload application
-
-
-Trying it out
--------------
-QEMU is an emulator and it can emulate an x86 machine. Please make sure your
-QEMU version is 2.3.0 or above to test this. You can run the payload with
-something like this:
-
- mkdir /tmp/efi
- cp /path/to/u-boot*.efi /tmp/efi
- qemu-system-x86_64 -bios bios.bin -hda fat:/tmp/efi/
-
-Add -nographic if you want to use the terminal for output. Once it starts
-type 'fs0:u-boot-payload.efi' to run the payload or 'fs0:u-boot-app.efi' to
-run the application. 'bios.bin' is the EFI 'BIOS'. Check [2] to obtain a
-prebuilt EFI BIOS for QEMU or you can build one from source as well.
-
-To try it on real hardware, put u-boot-app.efi on a suitable boot medium,
-such as a USB stick. Then you can type something like this to start it:
-
- fs0:u-boot-payload.efi
-
-(or fs0:u-boot-app.efi for the application)
-
-This will start the payload, copy U-Boot into RAM and start U-Boot. Note
-that EFI does not support booting a 64-bit application from a 32-bit
-EFI (or vice versa). Also it will often fail to print an error message if
-you get this wrong.
-
-
-Inner workings
-==============
-Here follow a few implementation notes for those who want to fiddle with
-this and perhaps contribute patches.
-
-The application and payload approaches sound similar but are in fact
-implemented completely differently.
-
-EFI Application
----------------
-For the application the whole of U-Boot is built as a shared library. The
-efi_main() function is in lib/efi/efi_app.c. It sets up some basic EFI
-functions with efi_init(), sets up U-Boot global_data, allocates memory for
-U-Boot's malloc(), etc. and enters the normal init sequence (board_init_f()
-and board_init_r()).
-
-Since U-Boot limits its memory access to the allocated regions very little
-special code is needed. The CONFIG_EFI_APP option controls a few things
-that need to change so 'git grep CONFIG_EFI_APP' may be instructive.
-The CONFIG_EFI option controls more general EFI adjustments.
-
-The only available driver is the serial driver. This calls back into EFI
-'boot services' to send and receive characters. Although it is implemented
-as a serial driver the console device is not necessarilly serial. If you
-boot EFI with video output then the 'serial' device will operate on your
-target devices's display instead and the device's USB keyboard will also
-work if connected. If you have both serial and video output, then both
-consoles will be active. Even though U-Boot does the same thing normally,
-These are features of EFI, not U-Boot.
-
-Very little code is involved in implementing the EFI application feature.
-U-Boot is highly portable. Most of the difficulty is in modifying the
-Makefile settings to pass the right build flags. In particular there is very
-little x86-specific code involved - you can find most of it in
-arch/x86/cpu. Porting to ARM (which can also use EFI if you are brave
-enough) should be straightforward.
-
-Use the 'reset' command to get back to EFI.
-
-EFI Payload
------------
-The payload approach is a different kettle of fish. It works by building
-U-Boot exactly as normal for your target board, then adding the entire
-image (including device tree) into a small EFI stub application responsible
-for booting it. The stub application is built as a normal EFI application
-except that it has a lot of data attached to it.
-
-The stub application is implemented in lib/efi/efi_stub.c. The efi_main()
-function is called by EFI. It is responsible for copying U-Boot from its
-original location into memory, disabling EFI boot services and starting
-U-Boot. U-Boot then starts as normal, relocates, starts all drivers, etc.
-
-The stub application is architecture-dependent. At present it has some
-x86-specific code and a comment at the top of efi_stub.c describes this.
-
-While the stub application does allocate some memory from EFI this is not
-used by U-Boot (the payload). In fact when U-Boot starts it has all of the
-memory available to it and can operate as it pleases (but see the next
-section).
-
-Tables
-------
-The payload can pass information to U-Boot in the form of EFI tables. At
-present this feature is used to pass the EFI memory map, an inordinately
-large list of memory regions. You can use the 'efi mem all' command to
-display this list. U-Boot uses the list to work out where to relocate
-itself.
-
-Although U-Boot can use any memory it likes, EFI marks some memory as used
-by 'run-time services', code that hangs around while U-Boot is running and
-is even present when Linux is running. This is common on x86 and provides
-a way for Linux to call back into the firmware to control things like CPU
-fan speed. U-Boot uses only 'conventional' memory, in EFI terminology. It
-will relocate itself to the top of the largest block of memory it can find
-below 4GB.
-
-Interrupts
-----------
-U-Boot drivers typically don't use interrupts. Since EFI enables interrupts
-it is possible that an interrupt will fire that U-Boot cannot handle. This
-seems to cause problems. For this reason the U-Boot payload runs with
-interrupts disabled at present.
-
-32/64-bit
----------
-While the EFI application can in principle be built as either 32- or 64-bit,
-only 32-bit is currently supported. This means that the application can only
-be used with 32-bit EFI.
-
-The payload stub can be build as either 32- or 64-bits. Only a small amount
-of code is built this way (see the extra- line in lib/efi/Makefile).
-Everything else is built as a normal U-Boot, so is always 32-bit on x86 at
-present.
-
Future work
------------
-This work could be extended in a number of ways:
-
-- Add a generic x86 EFI payload configuration. At present you need to modify
-an existing one, but mostly the low-level x86 code is disabled when booting
-on EFI anyway, so a generic 'EFI' board could be created with a suitable set
-of drivers enabled.
-- Add ARM support
-- Add 64-bit application support
-
-- Figure out how to solve the interrupt problem
-
-- Add more drivers to the application side (e.g. video, block devices, USB,
-environment access). This would mostly be an academic exercise as a strong
-use case is not readily apparent, but it might be fun.
-
-- Avoid turning off boot services in the stub. Instead allow U-Boot to make
-use of boot services in case it wants to. It is unclear what it might want
-though.
-
-Where is the code?
-------------------
-lib/efi
- payload stub, application, support code. Mostly arch-neutral
-
-arch/x86/lib/efi
- helper functions for the fake DRAM init, etc. These can be used by
- any board that runs as a payload.
-
-arch/x86/cpu/efi
- x86 support code for running as an EFI application
-
-board/efi/efi-x86/efi.c
- x86 board code for running as an EFI application
-
-common/cmd_efi.c
- the 'efi' command
-
---
-Ben Stoltz, Simon Glass
-Google, Inc
-July 2015
-
-[1] http://www.qemu.org
-[2] http://www.tianocore.org/ovmf/
-
--------------------------------------------------------------------------------
-
-EFI on U-Boot
-=============
-
-In addition to support for running U-Boot as a UEFI application, U-Boot itself
-can also expose the UEFI interfaces and thus allow UEFI payloads to run under
-it.
-
-In God's Name, Why?
--------------------
+Motivation
+----------
-With this support in place, you can run any UEFI payload (such as the Linux
+With this API support in place, you can run any UEFI payload (such as the Linux
kernel, grub2 or gummiboot) on U-Boot. This dramatically simplifies boot loader
configuration, as U-Boot based systems now look and feel (almost) the same way
as TianoCore based systems.
- Network device support
- Support for payload exit
- Payload Watchdog support
+
+[1] http://uefi.org/
--- /dev/null
+#
+# Copyright (C) 2015 Google, Inc
+#
+# SPDX-License-Identifier: GPL-2.0+
+#
+
+U-Boot on EFI
+=============
+This document provides information about U-Boot running on top of EFI, either
+as an application or just as a means of getting U-Boot onto a new platform.
+
+
+=========== Table of Contents ===========
+
+Motivation
+Status
+Build Instructions
+Trying it out
+Inner workings
+EFI Application
+EFI Payload
+Tables
+Interrupts
+32/64-bit
+Future work
+Where is the code?
+
+
+Motivation
+----------
+Running U-Boot on EFI is useful in several situations:
+
+- You have EFI running on a board but U-Boot does not natively support it
+fully yet. You can boot into U-Boot from EFI and use that until U-Boot is
+fully ported
+
+- You need to use an EFI implementation (e.g. UEFI) because your vendor
+requires it in order to provide support
+
+- You plan to use coreboot to boot into U-Boot but coreboot support does
+not currently exist for your platform. In the meantime you can use U-Boot
+on EFI and then move to U-Boot on coreboot when ready
+
+- You use EFI but want to experiment with a simpler alternative like U-Boot
+
+
+Status
+------
+Only x86 is supported at present. If you are using EFI on another architecture
+you may want to reconsider. However, much of the code is generic so could be
+ported.
+
+U-Boot supports running as an EFI application for 32-bit EFI only. This is
+not very useful since only a serial port is provided. You can look around at
+memory and type 'help' but that is about it.
+
+More usefully, U-Boot supports building itself as a payload for either 32-bit
+or 64-bit EFI. U-Boot is packaged up and loaded in its entirety by EFI. Once
+started, U-Boot changes to 32-bit mode (currently) and takes over the
+machine. You can use devices, boot a kernel, etc.
+
+
+Build Instructions
+------------------
+First choose a board that has EFI support and obtain an EFI implementation
+for that board. It will be either 32-bit or 64-bit. Alternatively, you can
+opt for using QEMU [1] and the OVMF [2], as detailed below.
+
+To build U-Boot as an EFI application (32-bit EFI required), enable CONFIG_EFI
+and CONFIG_EFI_APP. The efi-x86 config (efi-x86_defconfig) is set up for this.
+Just build U-Boot as normal, e.g.
+
+ make efi-x86_defconfig
+ make
+
+To build U-Boot as an EFI payload (32-bit or 64-bit EFI can be used), adjust an
+existing config (like qemu-x86_defconfig) to enable CONFIG_EFI, CONFIG_EFI_STUB
+and either CONFIG_EFI_STUB_32BIT or CONFIG_EFI_STUB_64BIT. All of these are
+boolean Kconfig options. Then build U-Boot as normal, e.g.
+
+ make qemu-x86_defconfig
+ make
+
+You will end up with one of these files depending on what you build for:
+
+ u-boot-app.efi - U-Boot EFI application
+ u-boot-payload.efi - U-Boot EFI payload application
+
+
+Trying it out
+-------------
+QEMU is an emulator and it can emulate an x86 machine. Please make sure your
+QEMU version is 2.3.0 or above to test this. You can run the payload with
+something like this:
+
+ mkdir /tmp/efi
+ cp /path/to/u-boot*.efi /tmp/efi
+ qemu-system-x86_64 -bios bios.bin -hda fat:/tmp/efi/
+
+Add -nographic if you want to use the terminal for output. Once it starts
+type 'fs0:u-boot-payload.efi' to run the payload or 'fs0:u-boot-app.efi' to
+run the application. 'bios.bin' is the EFI 'BIOS'. Check [2] to obtain a
+prebuilt EFI BIOS for QEMU or you can build one from source as well.
+
+To try it on real hardware, put u-boot-app.efi on a suitable boot medium,
+such as a USB stick. Then you can type something like this to start it:
+
+ fs0:u-boot-payload.efi
+
+(or fs0:u-boot-app.efi for the application)
+
+This will start the payload, copy U-Boot into RAM and start U-Boot. Note
+that EFI does not support booting a 64-bit application from a 32-bit
+EFI (or vice versa). Also it will often fail to print an error message if
+you get this wrong.
+
+
+Inner workings
+==============
+Here follow a few implementation notes for those who want to fiddle with
+this and perhaps contribute patches.
+
+The application and payload approaches sound similar but are in fact
+implemented completely differently.
+
+EFI Application
+---------------
+For the application the whole of U-Boot is built as a shared library. The
+efi_main() function is in lib/efi/efi_app.c. It sets up some basic EFI
+functions with efi_init(), sets up U-Boot global_data, allocates memory for
+U-Boot's malloc(), etc. and enters the normal init sequence (board_init_f()
+and board_init_r()).
+
+Since U-Boot limits its memory access to the allocated regions very little
+special code is needed. The CONFIG_EFI_APP option controls a few things
+that need to change so 'git grep CONFIG_EFI_APP' may be instructive.
+The CONFIG_EFI option controls more general EFI adjustments.
+
+The only available driver is the serial driver. This calls back into EFI
+'boot services' to send and receive characters. Although it is implemented
+as a serial driver the console device is not necessarilly serial. If you
+boot EFI with video output then the 'serial' device will operate on your
+target devices's display instead and the device's USB keyboard will also
+work if connected. If you have both serial and video output, then both
+consoles will be active. Even though U-Boot does the same thing normally,
+These are features of EFI, not U-Boot.
+
+Very little code is involved in implementing the EFI application feature.
+U-Boot is highly portable. Most of the difficulty is in modifying the
+Makefile settings to pass the right build flags. In particular there is very
+little x86-specific code involved - you can find most of it in
+arch/x86/cpu. Porting to ARM (which can also use EFI if you are brave
+enough) should be straightforward.
+
+Use the 'reset' command to get back to EFI.
+
+EFI Payload
+-----------
+The payload approach is a different kettle of fish. It works by building
+U-Boot exactly as normal for your target board, then adding the entire
+image (including device tree) into a small EFI stub application responsible
+for booting it. The stub application is built as a normal EFI application
+except that it has a lot of data attached to it.
+
+The stub application is implemented in lib/efi/efi_stub.c. The efi_main()
+function is called by EFI. It is responsible for copying U-Boot from its
+original location into memory, disabling EFI boot services and starting
+U-Boot. U-Boot then starts as normal, relocates, starts all drivers, etc.
+
+The stub application is architecture-dependent. At present it has some
+x86-specific code and a comment at the top of efi_stub.c describes this.
+
+While the stub application does allocate some memory from EFI this is not
+used by U-Boot (the payload). In fact when U-Boot starts it has all of the
+memory available to it and can operate as it pleases (but see the next
+section).
+
+Tables
+------
+The payload can pass information to U-Boot in the form of EFI tables. At
+present this feature is used to pass the EFI memory map, an inordinately
+large list of memory regions. You can use the 'efi mem all' command to
+display this list. U-Boot uses the list to work out where to relocate
+itself.
+
+Although U-Boot can use any memory it likes, EFI marks some memory as used
+by 'run-time services', code that hangs around while U-Boot is running and
+is even present when Linux is running. This is common on x86 and provides
+a way for Linux to call back into the firmware to control things like CPU
+fan speed. U-Boot uses only 'conventional' memory, in EFI terminology. It
+will relocate itself to the top of the largest block of memory it can find
+below 4GB.
+
+Interrupts
+----------
+U-Boot drivers typically don't use interrupts. Since EFI enables interrupts
+it is possible that an interrupt will fire that U-Boot cannot handle. This
+seems to cause problems. For this reason the U-Boot payload runs with
+interrupts disabled at present.
+
+32/64-bit
+---------
+While the EFI application can in principle be built as either 32- or 64-bit,
+only 32-bit is currently supported. This means that the application can only
+be used with 32-bit EFI.
+
+The payload stub can be build as either 32- or 64-bits. Only a small amount
+of code is built this way (see the extra- line in lib/efi/Makefile).
+Everything else is built as a normal U-Boot, so is always 32-bit on x86 at
+present.
+
+Future work
+-----------
+This work could be extended in a number of ways:
+
+- Add a generic x86 EFI payload configuration. At present you need to modify
+an existing one, but mostly the low-level x86 code is disabled when booting
+on EFI anyway, so a generic 'EFI' board could be created with a suitable set
+of drivers enabled.
+
+- Add ARM support
+
+- Add 64-bit application support
+
+- Figure out how to solve the interrupt problem
+
+- Add more drivers to the application side (e.g. video, block devices, USB,
+environment access). This would mostly be an academic exercise as a strong
+use case is not readily apparent, but it might be fun.
+
+- Avoid turning off boot services in the stub. Instead allow U-Boot to make
+use of boot services in case it wants to. It is unclear what it might want
+though.
+
+Where is the code?
+------------------
+lib/efi
+ payload stub, application, support code. Mostly arch-neutral
+
+arch/x86/lib/efi
+ helper functions for the fake DRAM init, etc. These can be used by
+ any board that runs as a payload.
+
+arch/x86/cpu/efi
+ x86 support code for running as an EFI application
+
+board/efi/efi-x86/efi.c
+ x86 board code for running as an EFI application
+
+common/cmd_efi.c
+ the 'efi' command
+
+--
+Ben Stoltz, Simon Glass
+Google, Inc
+July 2015
+
+[1] http://www.qemu.org
+[2] http://www.tianocore.org/ovmf/
projects / u-boot.git / commitdiff
