Change the UEFI documentation to Sphinx style and integrate it into the rest of the Sphinx generated documentation.
Remove the inaccurate TODO list in doc/uefi/uefi.rst.
Signed-off-by: Heinrich Schuchardt xypron.glpk@gmx.de --- MAINTAINERS | 4 +- doc/README.iscsi | 170 ------------------ doc/README.u-boot_on_efi | 252 -------------------------- doc/README.uefi | 352 ------------------------------------- doc/index.rst | 13 ++ doc/uefi/index.rst | 11 ++ doc/uefi/iscsi.rst | 180 +++++++++++++++++++ doc/uefi/u-boot_on_efi.rst | 235 +++++++++++++++++++++++++ doc/uefi/uefi.rst | 334 +++++++++++++++++++++++++++++++++++ 9 files changed, 774 insertions(+), 777 deletions(-) delete mode 100644 doc/README.iscsi delete mode 100644 doc/README.u-boot_on_efi delete mode 100644 doc/README.uefi create mode 100644 doc/uefi/index.rst create mode 100644 doc/uefi/iscsi.rst create mode 100644 doc/uefi/u-boot_on_efi.rst create mode 100644 doc/uefi/uefi.rst
diff --git a/MAINTAINERS b/MAINTAINERS index a72ccd0b58..12ad127adc 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -477,9 +477,7 @@ M: Heinrich Schuchardt xypron.glpk@gmx.de R: Alexander Graf agraf@csgraf.de S: Maintained T: git https://gitlab.denx.de/u-boot/custodians/u-boot-efi.git -F: doc/README.uefi -F: doc/README.iscsi -F: doc/efi.rst +F: doc/uefi/* F: include/capitalization.h F: include/charset.h F: include/cp1250.h diff --git a/doc/README.iscsi b/doc/README.iscsi deleted file mode 100644 index 3a12438f90..0000000000 --- a/doc/README.iscsi +++ /dev/null @@ -1,170 +0,0 @@ -# iSCSI booting with U-Boot and iPXE - -## Motivation - -U-Boot has only a reduced set of supported network protocols. The focus for -network booting has been on UDP based protocols. A TCP stack and HTTP support -are expected to be integrated in 2018 together with a wget command. - -For booting a diskless computer this leaves us with BOOTP or DHCP to get the -address of a boot script. TFTP or NFS can be used to load the boot script, the -operating system kernel and the initial file system (initrd). - -These protocols are insecure. The client cannot validate the authenticity -of the contacted servers. And the server cannot verify the identity of the -client. - -Furthermore the services providing the operating system loader or kernel are -not the ones that the operating system typically will use. Especially in a SAN -environment this makes updating the operating system a hassle. After installing -a new kernel version the boot files have to be copied to the TFTP server -directory. - -The HTTPS protocol provides certificate based validation of servers. Sensitive -data like passwords can be securely transmitted. - -The iSCSI protocol is used for connecting storage attached networks. It -provides mutual authentication using the CHAP protocol. It typically runs on -a TCP transport. - -Thus a better solution than DHCP/TFTP/NFS boot would be to load a boot script -via HTTPS and to download any other files needed for booting via iSCSI from the -same target where the operating system is installed. - -An alternative to implementing these protocols in U-Boot is to use an existing -software that can run on top of U-Boot. iPXE[1] is the "swiss army knife" of -network booting. It supports both HTTPS and iSCSI. It has a scripting engine for -fine grained control of the boot process and can provide a command shell. - -iPXE can be built as an EFI application (named snp.efi) which can be loaded and -run by U-Boot. - -## Boot sequence - -U-Boot loads the EFI application iPXE snp.efi using the bootefi command. This -application has network access via the simple network protocol offered by -U-Boot. - -iPXE executes its internal script. This script may optionally chain load a -secondary boot script via HTTPS or open a shell. - -For the further boot process iPXE connects to the iSCSI server. This includes -the mutual authentication using the CHAP protocol. After the authentication iPXE -has access to the iSCSI targets. - -For a selected iSCSI target iPXE sets up a handle with the block IO protocol. It -uses the ConnectController boot service of U-Boot to request U-Boot to connect a -file system driver. U-Boot reads from the iSCSI drive via the block IO protocol -offered by iPXE. It creates the partition handles and installs the simple file -protocol. Now iPXE can call the simple file protocol to load GRUB[2]. U-Boot -uses the block IO protocol offered by iPXE to fulfill the request. - -Once GRUB is started it uses the same block IO protocol to load Linux. Via -the EFI stub Linux is called as an EFI application:: - - +--------+ +--------+ - | | Runs | | - | U-Boot |========>| iPXE | - | EFI | | snp.efi| - +--------+ | | DHCP | | - | |<===|********|<========| | - | DHCP | | | Get IP | | - | Server | | | Address | | - | |===>|********|========>| | - +--------+ | | Response| | - | | | | - | | | | - +--------+ | | HTTPS | | - | |<===|********|<========| | - | HTTPS | | | Load | | - | Server | | | Script | | - | |===>|********|========>| | - +--------+ | | | | - | | | | - | | | | - +--------+ | | iSCSI | | - | |<===|********|<========| | - | iSCSI | | | Auth | | - | Server |===>|********|========>| | - | | | | | | - | | | | Loads | | - | |<===|********|<========| | +--------+ - | | | | GRUB | | Runs | | - | |===>|********|========>| |======>| GRUB | - | | | | | | | | - | | | | | | | | - | | | | | | Loads | | - | |<===|********|<========|********|<======| | +--------+ - | | | | | | Linux | | Runs | | - | |===>|********|========>|********|======>| |=====>| Linux | - | | | | | | | | | | - +--------+ +--------+ +--------+ +--------+ | | - | | - | | - | ~ ~ ~ ~| - -## Security - -The iSCSI protocol is not encrypted. The traffic could be secured using IPsec -but neither U-Boot nor iPXE does support this. So we should at least separate -the iSCSI traffic from all other network traffic. This can be achieved using a -virtual local area network (VLAN). - -## Configuration - -### iPXE - -For running iPXE on arm64 the bin-arm64-efi/snp.efi build target is needed:: - - git clone http://git.ipxe.org/ipxe.git - cd ipxe/src - make bin-arm64-efi/snp.efi -j6 EMBED=myscript.ipxe - -The available commands for the boot script are documented at: - -http://ipxe.org/cmd - -Credentials are managed as environment variables. These are described here: - -http://ipxe.org/cfg - -iPXE by default will put the CPU to rest when waiting for input. U-Boot does -not wake it up due to missing interrupt support. To avoid this behavior create -file src/config/local/nap.h:: - - /* nap.h */ - #undef NAP_EFIX86 - #undef NAP_EFIARM - #define NAP_NULL - -The supported commands in iPXE are controlled by an include, too. Putting the -following into src/config/local/general.h is sufficient for most use cases:: - - /* general.h */ - #define NSLOOKUP_CMD /* Name resolution command */ - #define PING_CMD /* Ping command */ - #define NTP_CMD /* NTP commands */ - #define VLAN_CMD /* VLAN commands */ - #define IMAGE_EFI /* EFI image support */ - #define DOWNLOAD_PROTO_HTTPS /* Secure Hypertext Transfer Protocol */ - #define DOWNLOAD_PROTO_FTP /* File Transfer Protocol */ - #define DOWNLOAD_PROTO_NFS /* Network File System Protocol */ - #define DOWNLOAD_PROTO_FILE /* Local file system access */ - -### Open-iSCSI - -When the root file system is on an iSCSI drive you should disable pings and set -the replacement timer to a high value [3]: - - node.conn[0].timeo.noop_out_interval = 0 - node.conn[0].timeo.noop_out_timeout = 0 - node.session.timeo.replacement_timeout = 86400 - -## Links - -* [1](https://ipxe.org) https://ipxe.org - iPXE open source boot firmware -* [2](https://www.gnu.org/software/grub/) https://www.gnu.org/software/grub/ - - GNU GRUB (Grand Unified Bootloader) -* [3](https://github.com/open-iscsi/open-iscsi/blob/master/README) - https://github.com/open-iscsi/open-iscsi/blob/master/README - - Open-iSCSI README diff --git a/doc/README.u-boot_on_efi b/doc/README.u-boot_on_efi deleted file mode 100644 index e12dd4e3e6..0000000000 --- a/doc/README.u-boot_on_efi +++ /dev/null @@ -1,252 +0,0 @@ -# SPDX-License-Identifier: GPL-2.0+ -# -# Copyright (C) 2015 Google, Inc - -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_app config (efi-x86_app_defconfig) is set up -for this. Just build U-Boot as normal, e.g. - - make efi-x86_app_defconfig - make - -To build U-Boot as an EFI payload (32-bit or 64-bit EFI can be used), enable -CONFIG_EFI, CONFIG_EFI_STUB, and select either CONFIG_EFI_STUB_32BIT or -CONFIG_EFI_STUB_64BIT. The efi-x86_payload configs (efi-x86_payload32_defconfig -and efi-x86_payload32_defconfig) are set up for this. Then build U-Boot as -normal, e.g. - - make efi-x86_payload32_defconfig (or efi-x86_payload64_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 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/cpu/efi - x86 support code for running as an EFI application and payload - -board/efi/efi-x86_app/efi.c - x86 board code for running as an EFI application - -board/efi/efi-x86_payload - generic x86 EFI payload board support code - -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/ diff --git a/doc/README.uefi b/doc/README.uefi deleted file mode 100644 index 1d1039a6ae..0000000000 --- a/doc/README.uefi +++ /dev/null @@ -1,352 +0,0 @@ -<!-- -SPDX-License-Identifier: GPL-2.0+ - -Copyright (c) 2018 Heinrich Schuchardt ---> - -# UEFI on U-Boot - -The Unified Extensible Firmware Interface Specification (UEFI) [1] has become -the default for booting on AArch64 and x86 systems. It provides a stable API for -the interaction of drivers and applications with the firmware. The API comprises -access to block storage, network, and console to name a few. The Linux kernel -and boot loaders like GRUB or the FreeBSD loader can be executed. - -## Development target - -The implementation of UEFI in U-Boot strives to reach the requirements described -in the "Embedded Base Boot Requirements (EBBR) Specification - Release v1.0" -[4]. The "Server Base Boot Requirements System Software on ARM Platforms" [5] -describes a superset of the EBBR specification and may be used as further -reference. - -A full blown UEFI implementation would contradict the U-Boot design principle -"keep it small". - -## Building for UEFI - -The UEFI standard supports only little-endian systems. The UEFI support can be -activated for ARM and x86 by specifying - - CONFIG_CMD_BOOTEFI=y - CONFIG_EFI_LOADER=y - -in the .config file. - -Support for attaching virtual block devices, e.g. iSCSI drives connected by the -loaded UEFI application [3], requires - - CONFIG_BLK=y - CONFIG_PARTITIONS=y - -### Executing a UEFI binary - -The bootefi command is used to start UEFI applications or to install UEFI -drivers. It takes two parameters - - bootefi <image address> [fdt address] - -* image address - the memory address of the UEFI binary -* fdt address - the memory address of the flattened device tree - -Below you find the output of an example session starting GRUB. - - => load mmc 0:2 ${fdt_addr_r} boot/dtb - 29830 bytes read in 14 ms (2 MiB/s) - => load mmc 0:1 ${kernel_addr_r} efi/debian/grubaa64.efi - reading efi/debian/grubaa64.efi - 120832 bytes read in 7 ms (16.5 MiB/s) - => bootefi ${kernel_addr_r} ${fdt_addr_r} - -The environment variable 'bootargs' is passed as load options in the UEFI system -table. The Linux kernel EFI stub uses the load options as command line -arguments. - -### Executing the boot manager - -The UEFI specification foresees to define boot entries and boot sequence via UEFI -variables. Booting according to these variables is possible via - - bootefi bootmgr [fdt address] - -As of U-Boot v2018.03 UEFI variables are not persisted and cannot be set at -runtime. - -### Executing the built in hello world application - -A hello world UEFI application can be built with - - CONFIG_CMD_BOOTEFI_HELLO_COMPILE=y - -It can be embedded into the U-Boot binary with - - CONFIG_CMD_BOOTEFI_HELLO=y - -The bootefi command is used to start the embedded hello world application. - - bootefi hello [fdt address] - -Below you find the output of an example session. - - => bootefi hello ${fdtcontroladdr} - ## Starting EFI application at 01000000 ... - WARNING: using memory device/image path, this may confuse some payloads! - Hello, world! - Running on UEFI 2.7 - Have SMBIOS table - Have device tree - Load options: root=/dev/sdb3 init=/sbin/init rootwait ro - ## Application terminated, r = 0 - -The environment variable fdtcontroladdr points to U-Boot's internal device tree -(if available). - -### Executing the built-in self-test - -An UEFI self-test suite can be embedded in U-Boot by building with - - CONFIG_CMD_BOOTEFI_SELFTEST=y - -For testing the UEFI implementation the bootefi command can be used to start the -self-test. - - bootefi selftest [fdt address] - -The environment variable 'efi_selftest' can be used to select a single test. If -it is not provided all tests are executed except those marked as 'on request'. -If the environment variable is set to 'list' a list of all tests is shown. - -Below you can find the output of an example session. - - => setenv efi_selftest simple network protocol - => bootefi selftest - Testing EFI API implementation - Selected test: 'simple network protocol' - Setting up 'simple network protocol' - Setting up 'simple network protocol' succeeded - Executing 'simple network protocol' - DHCP Discover - DHCP reply received from 192.168.76.2 (52:55:c0:a8:4c:02) - as broadcast message. - Executing 'simple network protocol' succeeded - Tearing down 'simple network protocol' - Tearing down 'simple network protocol' succeeded - Boot services terminated - Summary: 0 failures - Preparing for reset. Press any key. - -## The UEFI life cycle - -After the U-Boot platform has been initialized the UEFI API provides two kinds -of services - -* boot services and -* runtime services. - -The API can be extended by loading UEFI drivers which come in two variants - -* boot drivers and -* runtime drivers. - -UEFI drivers are installed with U-Boot's bootefi command. With the same command -UEFI applications can be executed. - -Loaded images of UEFI drivers stay in memory after returning to U-Boot while -loaded images of applications are removed from memory. - -An UEFI application (e.g. an operating system) that wants to take full control -of the system calls ExitBootServices. After a UEFI application calls -ExitBootServices - -* boot services are not available anymore -* timer events are stopped -* the memory used by U-Boot except for runtime services is released -* the memory used by boot time drivers is released - -So this is a point of no return. Afterwards the UEFI application can only return -to U-Boot by rebooting. - -## The UEFI object model - -UEFI offers a flexible and expandable object model. The objects in the UEFI API -are devices, drivers, and loaded images. These objects are referenced by -handles. - -The interfaces implemented by the objects are referred to as protocols. These -are identified by GUIDs. They can be installed and uninstalled by calling the -appropriate boot services. - -Handles are created by the InstallProtocolInterface or the -InstallMultipleProtocolinterfaces service if NULL is passed as handle. - -Handles are deleted when the last protocol has been removed with the -UninstallProtocolInterface or the UninstallMultipleProtocolInterfaces service. - -Devices offer the EFI_DEVICE_PATH_PROTOCOL. A device path is the concatenation -of device nodes. By their device paths all devices of a system are arranged in a -tree. - -Drivers offer the EFI_DRIVER_BINDING_PROTOCOL. This protocol is used to connect -a driver to devices (which are referenced as controllers in this context). - -Loaded images offer the EFI_LOADED_IMAGE_PROTOCOL. This protocol provides meta -information about the image and a pointer to the unload callback function. - -## The UEFI events - -In the UEFI terminology an event is a data object referencing a notification -function which is queued for calling when the event is signaled. The following -types of events exist: - -* periodic and single shot timer events -* exit boot services events, triggered by calling the ExitBootServices() service -* virtual address change events -* memory map change events -* read to boot events -* reset system events -* system table events -* events that are only triggered programmatically - -Events can be created with the CreateEvent service and deleted with CloseEvent -service. - -Events can be assigned to an event group. If any of the events in a group is -signaled, all other events in the group are also set to the signaled state. - -## The UEFI driver model - -A driver is specific for a single protocol installed on a device. To install a -driver on a device the ConnectController service is called. In this context -controller refers to the device for which the driver is installed. - -The relevant drivers are identified using the EFI_DRIVER_BINDING_PROTOCOL. This -protocol has has three functions: - -* supported - determines if the driver is compatible with the device -* start - installs the driver by opening the relevant protocol with - attribute EFI_OPEN_PROTOCOL_BY_DRIVER -* stop - uninstalls the driver - -The driver may create child controllers (child devices). E.g. a driver for block -IO devices will create the device handles for the partitions. The child -controllers will open the supported protocol with the attribute -EFI_OPEN_PROTOCOL_BY_CHILD_CONTROLLER. - -A driver can be detached from a device using the DisconnectController service. - -## U-Boot devices mapped as UEFI devices - -Some of the U-Boot devices are mapped as UEFI devices - -* block IO devices -* console -* graphical output -* network adapter - -As of U-Boot 2018.03 the logic for doing this is hard coded. - -The development target is to integrate the setup of these UEFI devices with the -U-Boot driver model. So when a U-Boot device is discovered a handle should be -created and the device path protocol and the relevant IO protocol should be -installed. The UEFI driver then would be attached by calling ConnectController. -When a U-Boot device is removed DisconnectController should be called. - -## UEFI devices mapped as U-Boot devices - -UEFI drivers binaries and applications may create new (virtual) devices, install -a protocol and call the ConnectController service. Now the matching UEFI driver -is determined by iterating over the implementations of the -EFI_DRIVER_BINDING_PROTOCOL. - -It is the task of the UEFI driver to create a corresponding U-Boot device and to -proxy calls for this U-Boot device to the controller. - -In U-Boot 2018.03 this has only been implemented for block IO devices. - -### UEFI uclass - -An UEFI uclass driver (lib/efi_driver/efi_uclass.c) has been created that -takes care of initializing the UEFI drivers and providing the -EFI_DRIVER_BINDING_PROTOCOL implementation for the UEFI drivers. - -A linker created list is used to keep track of the UEFI drivers. To create an -entry in the list the UEFI driver uses the U_BOOT_DRIVER macro specifying -UCLASS_EFI as the ID of its uclass, e.g. - - /* Identify as UEFI driver */ - U_BOOT_DRIVER(efi_block) = { - .name = "EFI block driver", - .id = UCLASS_EFI, - .ops = &driver_ops, - }; - -The available operations are defined via the structure struct efi_driver_ops. - - struct efi_driver_ops { - const efi_guid_t *protocol; - const efi_guid_t *child_protocol; - int (*bind)(efi_handle_t handle, void *interface); - }; - -When the supported() function of the EFI_DRIVER_BINDING_PROTOCOL is called the -uclass checks if the protocol GUID matches the protocol GUID of the UEFI driver. -In the start() function the bind() function of the UEFI driver is called after -checking the GUID. -The stop() function of the EFI_DRIVER_BINDING_PROTOCOL disconnects the child -controllers created by the UEFI driver and the UEFI driver. (In U-Boot v2013.03 -this is not yet completely implemented.) - -### UEFI block IO driver - -The UEFI block IO driver supports devices exposing the EFI_BLOCK_IO_PROTOCOL. - -When connected it creates a new U-Boot block IO device with interface type -IF_TYPE_EFI, adds child controllers mapping the partitions, and installs the -EFI_SIMPLE_FILE_SYSTEM_PROTOCOL on these. This can be used together with the -software iPXE to boot from iSCSI network drives [3]. - -This driver is only available if U-Boot is configured with - - CONFIG_BLK=y - CONFIG_PARTITIONS=y - -## TODOs as of U-Boot 2019.04 - -* unimplemented or incompletely implemented boot services - * Exit - call unload function, unload applications only - * ProtocolRegisterNotify - * UnloadImage - -* unimplemented or incompletely implemented runtime services - * SetVariable() ignores attribute EFI_VARIABLE_APPEND_WRITE - * QueryVariableInfo is not implemented - -* unimplemented events - * EVT_RUNTIME - * EVT_SIGNAL_VIRTUAL_ADDRESS_CHANGE - -* data model - * manage configuration tables in a linked list - -* UEFI drivers - * support DisconnectController for UEFI block devices. - -* support for CONFIG_EFI_LOADER in the sandbox (CONFIG_SANDBOX=y) - -* UEFI variables - * persistence - * runtime support - -* incompletely implemented protocols - * support version 0x00020000 of the EFI file protocol - -## Links - -* [1](http://uefi.org/specifications) - http://uefi.org/specifications - UEFI specifications -* [2](./driver-model/README.txt) doc/driver-model/README.txt - Driver model -* [3](./README.iscsi) doc/README.iscsi - iSCSI booting with U-Boot and iPXE -* [4](https://github.com/ARM-software/ebbr/releases/download/v1.0/ebbr-v1.0.pdf) - Embedded Base Boot Requirements (EBBR) Specification - Release v1.0 -* [5](https://developer.arm.com/docs/den0044/latest/server-base-boot-requirements-...) - Server Base Boot Requirements System Software on ARM Platforms - Version 1.1 diff --git a/doc/index.rst b/doc/index.rst index 9ae2e167bc..458f0d2d0e 100644 --- a/doc/index.rst +++ b/doc/index.rst @@ -15,8 +15,21 @@ if you want to help out. .. toctree:: :maxdepth: 2
+Unified Extensible Firmware (UEFI) +---------------------------------- + +U-Boot provides an implementation of the UEFI API allowing to run UEFI +compliant software like Linux, GRUB, and iPXE. Furthermore U-Boot itself +can be run an UEFI payload. + +.. toctree:: + :maxdepth: 2 + + uefi/index + Driver-Model documentation -------------------------- + The following holds information on the U-Boot device driver framework: driver-model, including the design details of itself and several driver subsystems. diff --git a/doc/uefi/index.rst b/doc/uefi/index.rst new file mode 100644 index 0000000000..b790a91f17 --- /dev/null +++ b/doc/uefi/index.rst @@ -0,0 +1,11 @@ +.. SPDX-License-Identifier: GPL-2.0+ + +Unified Extensible Firmware (UEFI) +================================== + +.. toctree:: + :maxdepth: 2 + + uefi.rst + u-boot_on_efi.rst + iscsi.rst diff --git a/doc/uefi/iscsi.rst b/doc/uefi/iscsi.rst new file mode 100644 index 0000000000..aa844a7cc3 --- /dev/null +++ b/doc/uefi/iscsi.rst @@ -0,0 +1,180 @@ +.. SPDX-License-Identifier: GPL-2.0+ +.. Copyright (c) 2018 Heinrich Schuchardt + +iSCSI booting with U-Boot and iPXE +================================== + +Motivation +---------- + +U-Boot has only a reduced set of supported network protocols. The focus for +network booting has been on UDP based protocols. A TCP stack and HTTP support +are expected to be integrated in 2018 together with a wget command. + +For booting a diskless computer this leaves us with BOOTP or DHCP to get the +address of a boot script. TFTP or NFS can be used to load the boot script, the +operating system kernel and the initial file system (initrd). + +These protocols are insecure. The client cannot validate the authenticity +of the contacted servers. And the server cannot verify the identity of the +client. + +Furthermore the services providing the operating system loader or kernel are +not the ones that the operating system typically will use. Especially in a SAN +environment this makes updating the operating system a hassle. After installing +a new kernel version the boot files have to be copied to the TFTP server +directory. + +The HTTPS protocol provides certificate based validation of servers. Sensitive +data like passwords can be securely transmitted. + +The iSCSI protocol is used for connecting storage attached networks. It +provides mutual authentication using the CHAP protocol. It typically runs on +a TCP transport. + +Thus a better solution than DHCP/TFTP/NFS boot would be to load a boot script +via HTTPS and to download any other files needed for booting via iSCSI from the +same target where the operating system is installed. + +An alternative to implementing these protocols in U-Boot is to use an existing +software that can run on top of U-Boot. iPXE[1] is the "swiss army knife" of +network booting. It supports both HTTPS and iSCSI. It has a scripting engine for +fine grained control of the boot process and can provide a command shell. + +iPXE can be built as an EFI application (named snp.efi) which can be loaded and +run by U-Boot. + +Boot sequence +------------- + +U-Boot loads the EFI application iPXE snp.efi using the bootefi command. This +application has network access via the simple network protocol offered by +U-Boot. + +iPXE executes its internal script. This script may optionally chain load a +secondary boot script via HTTPS or open a shell. + +For the further boot process iPXE connects to the iSCSI server. This includes +the mutual authentication using the CHAP protocol. After the authentication iPXE +has access to the iSCSI targets. + +For a selected iSCSI target iPXE sets up a handle with the block IO protocol. It +uses the ConnectController boot service of U-Boot to request U-Boot to connect a +file system driver. U-Boot reads from the iSCSI drive via the block IO protocol +offered by iPXE. It creates the partition handles and installs the simple file +protocol. Now iPXE can call the simple file protocol to load GRUB[2]. U-Boot +uses the block IO protocol offered by iPXE to fulfill the request. + +Once GRUB is started it uses the same block IO protocol to load Linux. Via +the EFI stub Linux is called as an EFI application:: + + +--------+ +--------+ + | | Runs | | + | U-Boot |========>| iPXE | + | EFI | | snp.efi| + +--------+ | | DHCP | | + | |<===|********|<========| | + | DHCP | | | Get IP | | + | Server | | | Address | | + | |===>|********|========>| | + +--------+ | | Response| | + | | | | + | | | | + +--------+ | | HTTPS | | + | |<===|********|<========| | + | HTTPS | | | Load | | + | Server | | | Script | | + | |===>|********|========>| | + +--------+ | | | | + | | | | + | | | | + +--------+ | | iSCSI | | + | |<===|********|<========| | + | iSCSI | | | Auth | | + | Server |===>|********|========>| | + | | | | | | + | | | | Loads | | + | |<===|********|<========| | +--------+ + | | | | GRUB | | Runs | | + | |===>|********|========>| |======>| GRUB | + | | | | | | | | + | | | | | | | | + | | | | | | Loads | | + | |<===|********|<========|********|<======| | +--------+ + | | | | | | Linux | | Runs | | + | |===>|********|========>|********|======>| |=====>| Linux | + | | | | | | | | | | + +--------+ +--------+ +--------+ +--------+ | | + | | + | | + | ~ ~ ~ ~| + +Security +-------- + +The iSCSI protocol is not encrypted. The traffic could be secured using IPsec +but neither U-Boot nor iPXE does support this. So we should at least separate +the iSCSI traffic from all other network traffic. This can be achieved using a +virtual local area network (VLAN). + +Configuration +------------- + +iPXE +~~~~ + +For running iPXE on arm64 the bin-arm64-efi/snp.efi build target is needed:: + + git clone http://git.ipxe.org/ipxe.git + cd ipxe/src + make bin-arm64-efi/snp.efi -j6 EMBED=myscript.ipxe + +The available commands for the boot script are documented at: + +http://ipxe.org/cmd + +Credentials are managed as environment variables. These are described here: + +http://ipxe.org/cfg + +iPXE by default will put the CPU to rest when waiting for input. U-Boot does +not wake it up due to missing interrupt support. To avoid this behavior create +file src/config/local/nap.h:: + + /* nap.h */ + #undef NAP_EFIX86 + #undef NAP_EFIARM + #define NAP_NULL + +The supported commands in iPXE are controlled by an include, too. Putting the +following into src/config/local/general.h is sufficient for most use cases:: + + /* general.h */ + #define NSLOOKUP_CMD /* Name resolution command */ + #define PING_CMD /* Ping command */ + #define NTP_CMD /* NTP commands */ + #define VLAN_CMD /* VLAN commands */ + #define IMAGE_EFI /* EFI image support */ + #define DOWNLOAD_PROTO_HTTPS /* Secure Hypertext Transfer Protocol */ + #define DOWNLOAD_PROTO_FTP /* File Transfer Protocol */ + #define DOWNLOAD_PROTO_NFS /* Network File System Protocol */ + #define DOWNLOAD_PROTO_FILE /* Local file system access */ + +Open-iSCSI +~~~~~~~~~~ + +When the root file system is on an iSCSI drive you should disable pings and set +the replacement timer to a high value [3]: + + node.conn[0].timeo.noop_out_interval = 0 + node.conn[0].timeo.noop_out_timeout = 0 + node.session.timeo.replacement_timeout = 86400 + +Links +----- + +* [1] https://ipxe.org - iPXE open source boot firmware +* [2] https://www.gnu.org/software/grub/ - + GNU GRUB (Grand Unified Bootloader) +* [3] https://github.com/open-iscsi/open-iscsi/blob/master/README - + Open-iSCSI README diff --git a/doc/uefi/u-boot_on_efi.rst b/doc/uefi/u-boot_on_efi.rst new file mode 100644 index 0000000000..139173bc7a --- /dev/null +++ b/doc/uefi/u-boot_on_efi.rst @@ -0,0 +1,235 @@ +.. SPDX-License-Identifier: GPL-2.0+ +.. Copyright (C) 2015 Google, Inc + +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. + + +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_app config (efi-x86_app_defconfig) is set up +for this. Just build U-Boot as normal, e.g. + + make efi-x86_app_defconfig + make + +To build U-Boot as an EFI payload (32-bit or 64-bit EFI can be used), enable +CONFIG_EFI, CONFIG_EFI_STUB, and select either CONFIG_EFI_STUB_32BIT or +CONFIG_EFI_STUB_64BIT. The efi-x86_payload configs (efi-x86_payload32_defconfig +and efi-x86_payload32_defconfig) are set up for this. Then build U-Boot as +normal, e.g. + + make efi-x86_payload32_defconfig (or efi-x86_payload64_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 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/cpu/efi + x86 support code for running as an EFI application and payload + +board/efi/efi-x86_app/efi.c + x86 board code for running as an EFI application + +board/efi/efi-x86_payload + generic x86 EFI payload board support code + +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/ diff --git a/doc/uefi/uefi.rst b/doc/uefi/uefi.rst new file mode 100644 index 0000000000..476117bfc5 --- /dev/null +++ b/doc/uefi/uefi.rst @@ -0,0 +1,334 @@ +.. SPDX-License-Identifier: GPL-2.0+ +.. Copyright (c) 2018 Heinrich Schuchardt + +UEFI on U-Boot +============== + +The Unified Extensible Firmware Interface Specification (UEFI) [1] has become +the default for booting on AArch64 and x86 systems. It provides a stable API for +the interaction of drivers and applications with the firmware. The API comprises +access to block storage, network, and console to name a few. The Linux kernel +and boot loaders like GRUB or the FreeBSD loader can be executed. + +Development target +------------------ + +The implementation of UEFI in U-Boot strives to reach the requirements described +in the "Embedded Base Boot Requirements (EBBR) Specification - Release v1.0" +[4]. The "Server Base Boot Requirements System Software on ARM Platforms" [5] +describes a superset of the EBBR specification and may be used as further +reference. + +A full blown UEFI implementation would contradict the U-Boot design principle +"keep it small". + +Building U-Boot for UEFI +------------------------ + +The UEFI standard supports only little-endian systems. The UEFI support can be +activated for ARM and x86 by specifying:: + + CONFIG_CMD_BOOTEFI=y + CONFIG_EFI_LOADER=y + +in the .config file. + +Support for attaching virtual block devices, e.g. iSCSI drives connected by the +loaded UEFI application [3], requires:: + + CONFIG_BLK=y + CONFIG_PARTITIONS=y + +Executing a UEFI binary +~~~~~~~~~~~~~~~~~~~~~~~ + +The bootefi command is used to start UEFI applications or to install UEFI +drivers. It takes two parameters:: + + bootefi <image address> [fdt address] + +* image address - the memory address of the UEFI binary +* fdt address - the memory address of the flattened device tree + +Below you find the output of an example session starting GRUB:: + + => load mmc 0:2 ${fdt_addr_r} boot/dtb + 29830 bytes read in 14 ms (2 MiB/s) + => load mmc 0:1 ${kernel_addr_r} efi/debian/grubaa64.efi + reading efi/debian/grubaa64.efi + 120832 bytes read in 7 ms (16.5 MiB/s) + => bootefi ${kernel_addr_r} ${fdt_addr_r} + +The environment variable 'bootargs' is passed as load options in the UEFI system +table. The Linux kernel EFI stub uses the load options as command line +arguments. + +Executing the boot manager +~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The UEFI specification foresees to define boot entries and boot sequence via UEFI +variables. Booting according to these variables is possible via:: + + bootefi bootmgr [fdt address] + +As of U-Boot v2018.03 UEFI variables are not persisted and cannot be set at +runtime. + +Executing the built in hello world application +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +A hello world UEFI application can be built with:: + + CONFIG_CMD_BOOTEFI_HELLO_COMPILE=y + +It can be embedded into the U-Boot binary with:: + + CONFIG_CMD_BOOTEFI_HELLO=y + +The bootefi command is used to start the embedded hello world application:: + + bootefi hello [fdt address] + +Below you find the output of an example session:: + + => bootefi hello ${fdtcontroladdr} + ## Starting EFI application at 01000000 ... + WARNING: using memory device/image path, this may confuse some payloads! + Hello, world! + Running on UEFI 2.7 + Have SMBIOS table + Have device tree + Load options: root=/dev/sdb3 init=/sbin/init rootwait ro + ## Application terminated, r = 0 + +The environment variable fdtcontroladdr points to U-Boot's internal device tree +(if available). + +Executing the built-in self-test +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +An UEFI self-test suite can be embedded in U-Boot by building with:: + + CONFIG_CMD_BOOTEFI_SELFTEST=y + +For testing the UEFI implementation the bootefi command can be used to start the +self-test:: + + bootefi selftest [fdt address] + +The environment variable 'efi_selftest' can be used to select a single test. If +it is not provided all tests are executed except those marked as 'on request'. +If the environment variable is set to 'list' a list of all tests is shown. + +Below you can find the output of an example session:: + + => setenv efi_selftest simple network protocol + => bootefi selftest + Testing EFI API implementation + Selected test: 'simple network protocol' + Setting up 'simple network protocol' + Setting up 'simple network protocol' succeeded + Executing 'simple network protocol' + DHCP Discover + DHCP reply received from 192.168.76.2 (52:55:c0:a8:4c:02) + as broadcast message. + Executing 'simple network protocol' succeeded + Tearing down 'simple network protocol' + Tearing down 'simple network protocol' succeeded + Boot services terminated + Summary: 0 failures + Preparing for reset. Press any key. + +The UEFI life cycle +------------------- + +After the U-Boot platform has been initialized the UEFI API provides two kinds +of services + +* boot services and +* runtime services. + +The API can be extended by loading UEFI drivers which come in two variants + +* boot drivers and +* runtime drivers. + +UEFI drivers are installed with U-Boot's bootefi command. With the same command +UEFI applications can be executed. + +Loaded images of UEFI drivers stay in memory after returning to U-Boot while +loaded images of applications are removed from memory. + +An UEFI application (e.g. an operating system) that wants to take full control +of the system calls ExitBootServices. After a UEFI application calls +ExitBootServices + +* boot services are not available anymore +* timer events are stopped +* the memory used by U-Boot except for runtime services is released +* the memory used by boot time drivers is released + +So this is a point of no return. Afterwards the UEFI application can only return +to U-Boot by rebooting. + +The UEFI object model +--------------------- + +UEFI offers a flexible and expandable object model. The objects in the UEFI API +are devices, drivers, and loaded images. These objects are referenced by +handles. + +The interfaces implemented by the objects are referred to as protocols. These +are identified by GUIDs. They can be installed and uninstalled by calling the +appropriate boot services. + +Handles are created by the InstallProtocolInterface or the +InstallMultipleProtocolinterfaces service if NULL is passed as handle. + +Handles are deleted when the last protocol has been removed with the +UninstallProtocolInterface or the UninstallMultipleProtocolInterfaces service. + +Devices offer the EFI_DEVICE_PATH_PROTOCOL. A device path is the concatenation +of device nodes. By their device paths all devices of a system are arranged in a +tree. + +Drivers offer the EFI_DRIVER_BINDING_PROTOCOL. This protocol is used to connect +a driver to devices (which are referenced as controllers in this context). + +Loaded images offer the EFI_LOADED_IMAGE_PROTOCOL. This protocol provides meta +information about the image and a pointer to the unload callback function. + +The UEFI events +--------------- + +In the UEFI terminology an event is a data object referencing a notification +function which is queued for calling when the event is signaled. The following +types of events exist: + +* periodic and single shot timer events +* exit boot services events, triggered by calling the ExitBootServices() service +* virtual address change events +* memory map change events +* read to boot events +* reset system events +* system table events +* events that are only triggered programmatically + +Events can be created with the CreateEvent service and deleted with CloseEvent +service. + +Events can be assigned to an event group. If any of the events in a group is +signaled, all other events in the group are also set to the signaled state. + +The UEFI driver model +--------------------- + +A driver is specific for a single protocol installed on a device. To install a +driver on a device the ConnectController service is called. In this context +controller refers to the device for which the driver is installed. + +The relevant drivers are identified using the EFI_DRIVER_BINDING_PROTOCOL. This +protocol has has three functions: + +* supported - determines if the driver is compatible with the device +* start - installs the driver by opening the relevant protocol with + attribute EFI_OPEN_PROTOCOL_BY_DRIVER +* stop - uninstalls the driver + +The driver may create child controllers (child devices). E.g. a driver for block +IO devices will create the device handles for the partitions. The child +controllers will open the supported protocol with the attribute +EFI_OPEN_PROTOCOL_BY_CHILD_CONTROLLER. + +A driver can be detached from a device using the DisconnectController service. + +U-Boot devices mapped as UEFI devices +------------------------------------- + +Some of the U-Boot devices are mapped as UEFI devices + +* block IO devices +* console +* graphical output +* network adapter + +As of U-Boot 2018.03 the logic for doing this is hard coded. + +The development target is to integrate the setup of these UEFI devices with the +U-Boot driver model. So when a U-Boot device is discovered a handle should be +created and the device path protocol and the relevant IO protocol should be +installed. The UEFI driver then would be attached by calling ConnectController. +When a U-Boot device is removed DisconnectController should be called. + +UEFI devices mapped as U-Boot devices +------------------------------------- + +UEFI drivers binaries and applications may create new (virtual) devices, install +a protocol and call the ConnectController service. Now the matching UEFI driver +is determined by iterating over the implementations of the +EFI_DRIVER_BINDING_PROTOCOL. + +It is the task of the UEFI driver to create a corresponding U-Boot device and to +proxy calls for this U-Boot device to the controller. + +In U-Boot 2018.03 this has only been implemented for block IO devices. + +UEFI uclass +~~~~~~~~~~~ + +An UEFI uclass driver (lib/efi_driver/efi_uclass.c) has been created that +takes care of initializing the UEFI drivers and providing the +EFI_DRIVER_BINDING_PROTOCOL implementation for the UEFI drivers. + +A linker created list is used to keep track of the UEFI drivers. To create an +entry in the list the UEFI driver uses the U_BOOT_DRIVER macro specifying +UCLASS_EFI as the ID of its uclass, e.g:: + + /* Identify as UEFI driver */ + U_BOOT_DRIVER(efi_block) = { + .name = "EFI block driver", + .id = UCLASS_EFI, + .ops = &driver_ops, + }; + +The available operations are defined via the structure struct efi_driver_ops:: + + struct efi_driver_ops { + const efi_guid_t *protocol; + const efi_guid_t *child_protocol; + int (*bind)(efi_handle_t handle, void *interface); + }; + +When the supported() function of the EFI_DRIVER_BINDING_PROTOCOL is called the +uclass checks if the protocol GUID matches the protocol GUID of the UEFI driver. +In the start() function the bind() function of the UEFI driver is called after +checking the GUID. +The stop() function of the EFI_DRIVER_BINDING_PROTOCOL disconnects the child +controllers created by the UEFI driver and the UEFI driver. (In U-Boot v2013.03 +this is not yet completely implemented.) + +UEFI block IO driver +~~~~~~~~~~~~~~~~~~~~ + +The UEFI block IO driver supports devices exposing the EFI_BLOCK_IO_PROTOCOL. + +When connected it creates a new U-Boot block IO device with interface type +IF_TYPE_EFI, adds child controllers mapping the partitions, and installs the +EFI_SIMPLE_FILE_SYSTEM_PROTOCOL on these. This can be used together with the +software iPXE to boot from iSCSI network drives [3]. + +This driver is only available if U-Boot is configured with + + CONFIG_BLK=y + CONFIG_PARTITIONS=y + +Links +----- + +* [1] http://uefi.org/specifications - UEFI specifications +* [2] :doc:`../driver-model/index` +* [3] :doc:`iscsi` +* [4] https://github.com/ARM-software/ebbr/releases/download/v1.0/ebbr-v1.0.pdf - + Embedded Base Boot Requirements (EBBR) Specification - Release v1.0 +* [5] https://developer.arm.com/docs/den0044/latest/server-base-boot-requirements-... - + Server Base Boot Requirements System Software on ARM Platforms - Version 1.1 -- 2.20.1