README.efi describes two different concepts: * U-Boot exposing the UEFI API * U-Boot running on top of UEFI.
This patch splits the document in two. Religious references are removed.
The separation of the concepts makes sense before detailing the internals of U-Boot exposing the UEFI API in a future patch.
Signed-off-by: Heinrich Schuchardt xypron.glpk@gmx.de --- v2 Do not set maintainer for README.u-boot_on_efi --- MAINTAINERS | 1 + doc/README.efi | 275 ++--------------------------------------------- doc/README.u-boot_on_efi | 259 ++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 271 insertions(+), 264 deletions(-) create mode 100644 doc/README.u-boot_on_efi
diff --git a/MAINTAINERS b/MAINTAINERS index 0aecc18a6c..6d4f335d4a 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -289,6 +289,7 @@ EFI PAYLOAD M: Alexander Graf agraf@suse.de S: Maintained T: git git://github.com/agraf/u-boot.git +F: doc/README.efi F: doc/README.iscsi F: include/efi* F: lib/efi*/ diff --git a/doc/README.efi b/doc/README.efi index 66259f3e26..956f5bfa0c 100644 --- a/doc/README.efi +++ b/doc/README.efi @@ -4,279 +4,24 @@ # 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. @@ -337,3 +82,5 @@ have) - Network device support - Support for payload exit - Payload Watchdog support + +[1] http://uefi.org/ diff --git a/doc/README.u-boot_on_efi b/doc/README.u-boot_on_efi new file mode 100644 index 0000000000..298b94e342 --- /dev/null +++ b/doc/README.u-boot_on_efi @@ -0,0 +1,259 @@ +# +# 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/