doc/uefi/uefi.rst - platform/external/u-boot - Gitiles

 .. 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"
 [2]. The "Server Base Boot Requirements System Software on ARM Platforms" [3]
 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 [4], 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.

 Launching a UEFI binary from a FIT image
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 A signed FIT image can be used to securely boot a UEFI image via the
 bootm command. This feature is available if U-Boot is configured with::

     CONFIG_BOOTM_EFI=y

 A sample configuration is provided as file doc/uImage.FIT/uefi.its.

 Below you find the output of an example session starting GRUB::

     => load mmc 0:1 ${kernel_addr_r} image.fit
     4620426 bytes read in 83 ms (53.1 MiB/s)
     => bootm ${kernel_addr_r}#config-grub-nofdt
     ## Loading kernel from FIT Image at 40400000 ...
        Using 'config-grub-nofdt' configuration
        Verifying Hash Integrity ... sha256,rsa2048:dev+ OK
        Trying 'efi-grub' kernel subimage
          Description:  GRUB EFI Firmware
          Created:      2019-11-20   8:18:16 UTC
          Type:         Kernel Image (no loading done)
          Compression:  uncompressed
          Data Start:   0x404000d0
          Data Size:    450560 Bytes = 440 KiB
          Hash algo:    sha256
          Hash value:   4dbee00021112df618f58b3f7cf5e1595533d543094064b9ce991e8b054a9eec
        Verifying Hash Integrity ... sha256+ OK
        XIP Kernel Image (no loading done)
     ## Transferring control to EFI (at address 404000d0) ...
     Welcome to GRUB!

 See doc/uImage.FIT/howto.txt for an introduction to FIT images.

 Configuring UEFI secure boot
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 UEFI specification[1] defines a secure way of executing UEFI images
 by verifying a signature (or message digest) of image with certificates.
 This feature on U-Boot is enabled with::

     CONFIG_UEFI_SECURE_BOOT=y

 To make the boot sequence safe, you need to establish a chain of trust;
 In UEFI secure boot, you can make it with the UEFI variables, "PK"
 (Platform Key), "KEK" (Key Exchange Keys), "db" (white list database)
 and "dbx" (black list database).

 There are many online documents that describe what UEFI secure boot is
 and how it works. Please consult some of them for details.

 Here is a simple example that you can follow for your initial attempt
 (Please note that the actual steps would absolutely depend on your system
 and environment.):

 1. Install utility commands on your host
     * openssl
     * efitools
     * sbsigntool

 2. Create signing keys and key database files on your host
     for PK::

         $ openssl req -x509 -sha256 -newkey rsa:2048 -subj /CN=TEST_PK/ \
                 -keyout PK.key -out PK.crt -nodes -days 365
         $ cert-to-efi-sig-list -g 11111111-2222-3333-4444-123456789abc \
                 PK.crt PK.esl;
         $ sign-efi-sig-list -c PK.crt -k PK.key PK PK.esl PK.auth

     for KEK::

         $ openssl req -x509 -sha256 -newkey rsa:2048 -subj /CN=TEST_KEK/ \
                 -keyout KEK.key -out KEK.crt -nodes -days 365
         $ cert-to-efi-sig-list -g 11111111-2222-3333-4444-123456789abc \
                 KEK.crt KEK.esl
         $ sign-efi-sig-list -c PK.crt -k PK.key KEK KEK.esl KEK.auth

     for db::

         $ openssl req -x509 -sha256 -newkey rsa:2048 -subj /CN=TEST_db/ \
                 -keyout db.key -out db.crt -nodes -days 365
         $ cert-to-efi-sig-list -g 11111111-2222-3333-4444-123456789abc \
                 db.crt db.esl
         $ sign-efi-sig-list -c KEK.crt -k KEK.key db db.esl db.auth

     Copy \*.auth to media, say mmc, that is accessible from U-Boot.

 3. Sign an image with one key in "db" on your host::

     $ sbsign --key db.key --cert db.crt helloworld.efi

 4. Install keys on your board::

     ==> fatload mmc 0:1 <tmpaddr> PK.auth
     ==> setenv -e -nv -bs -rt -at -i <tmpaddr>,$filesize PK
     ==> fatload mmc 0:1 <tmpaddr> KEK.auth
     ==> setenv -e -nv -bs -rt -at -i <tmpaddr>,$filesize KEK
     ==> fatload mmc 0:1 <tmpaddr> db.auth
     ==> setenv -e -nv -bs -rt -at -i <tmpaddr>,$filesize db

 5. Set up boot parameters on your board::

     ==> efidebug boot add 1 HELLO mmc 0:1 /helloworld.efi.signed ""

 Then your board runs that image from Boot manager (See below).
 You can also try this sequence by running Pytest, test_efi_secboot,
 on sandbox::

     $ cd <U-Boot source directory>
     $ pytest.py test/py/tests/test_efi_secboot/test_signed.py --bd sandbox

 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
 * runtime services

 The API can be extended by loading UEFI drivers which come in two variants:

 * boot drivers
 * 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 [5]. 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 [4].

 This driver is only available if U-Boot is configured with::

     CONFIG_BLK=y
     CONFIG_PARTITIONS=y

 Miscellaneous
 -------------

 Load file 2 protocol
 ~~~~~~~~~~~~~~~~~~~~

 The load file 2 protocol can be used by the Linux kernel to load the initial
 RAM disk. U-Boot can be configured to provide an implementation with::

     EFI_LOAD_FILE2_INITRD=y
     EFI_INITRD_FILESPEC=interface dev:part path_to_initrd

 Links
 -----

 * [1] http://uefi.org/specifications - UEFI specifications
 * [2] https://github.com/ARM-software/ebbr/releases/download/v1.0/ebbr-v1.0.pdf -
   Embedded Base Boot Requirements (EBBR) Specification - Release v1.0
 * [3] https://developer.arm.com/docs/den0044/latest/server-base-boot-requirements-system-software-on-arm-platforms-version-11 -
   Server Base Boot Requirements System Software on ARM Platforms - Version 1.1
 * [4] :doc:`iscsi`
 * [5] :doc:`../driver-model/index`
	.. 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"
	[2]. The "Server Base Boot Requirements System Software on ARM Platforms" [3]
	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 [4], 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.

	Launching a UEFI binary from a FIT image
	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	A signed FIT image can be used to securely boot a UEFI image via the
	bootm command. This feature is available if U-Boot is configured with::

	CONFIG_BOOTM_EFI=y

	A sample configuration is provided as file doc/uImage.FIT/uefi.its.

	Below you find the output of an example session starting GRUB::

	=> load mmc 0:1 ${kernel_addr_r} image.fit
	4620426 bytes read in 83 ms (53.1 MiB/s)
	=> bootm ${kernel_addr_r}#config-grub-nofdt
	## Loading kernel from FIT Image at 40400000 ...
	Using 'config-grub-nofdt' configuration
	Verifying Hash Integrity ... sha256,rsa2048:dev+ OK
	Trying 'efi-grub' kernel subimage
	Description: GRUB EFI Firmware
	Created: 2019-11-20 8:18:16 UTC
	Type: Kernel Image (no loading done)
	Compression: uncompressed
	Data Start: 0x404000d0
	Data Size: 450560 Bytes = 440 KiB
	Hash algo: sha256
	Hash value: 4dbee00021112df618f58b3f7cf5e1595533d543094064b9ce991e8b054a9eec
	Verifying Hash Integrity ... sha256+ OK
	XIP Kernel Image (no loading done)
	## Transferring control to EFI (at address 404000d0) ...
	Welcome to GRUB!

	See doc/uImage.FIT/howto.txt for an introduction to FIT images.

	Configuring UEFI secure boot
	~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	UEFI specification[1] defines a secure way of executing UEFI images
	by verifying a signature (or message digest) of image with certificates.
	This feature on U-Boot is enabled with::

	CONFIG_UEFI_SECURE_BOOT=y

	To make the boot sequence safe, you need to establish a chain of trust;
	In UEFI secure boot, you can make it with the UEFI variables, "PK"
	(Platform Key), "KEK" (Key Exchange Keys), "db" (white list database)
	and "dbx" (black list database).

	There are many online documents that describe what UEFI secure boot is
	and how it works. Please consult some of them for details.

	Here is a simple example that you can follow for your initial attempt
	(Please note that the actual steps would absolutely depend on your system
	and environment.):

	1. Install utility commands on your host
	* openssl
	* efitools
	* sbsigntool

	2. Create signing keys and key database files on your host
	for PK::

	$ openssl req -x509 -sha256 -newkey rsa:2048 -subj /CN=TEST_PK/ \
	-keyout PK.key -out PK.crt -nodes -days 365
	$ cert-to-efi-sig-list -g 11111111-2222-3333-4444-123456789abc \
	PK.crt PK.esl;
	$ sign-efi-sig-list -c PK.crt -k PK.key PK PK.esl PK.auth

	for KEK::

	$ openssl req -x509 -sha256 -newkey rsa:2048 -subj /CN=TEST_KEK/ \
	-keyout KEK.key -out KEK.crt -nodes -days 365
	$ cert-to-efi-sig-list -g 11111111-2222-3333-4444-123456789abc \
	KEK.crt KEK.esl
	$ sign-efi-sig-list -c PK.crt -k PK.key KEK KEK.esl KEK.auth

	for db::

	$ openssl req -x509 -sha256 -newkey rsa:2048 -subj /CN=TEST_db/ \
	-keyout db.key -out db.crt -nodes -days 365
	$ cert-to-efi-sig-list -g 11111111-2222-3333-4444-123456789abc \
	db.crt db.esl
	$ sign-efi-sig-list -c KEK.crt -k KEK.key db db.esl db.auth

	Copy \*.auth to media, say mmc, that is accessible from U-Boot.

	3. Sign an image with one key in "db" on your host::

	$ sbsign --key db.key --cert db.crt helloworld.efi

	4. Install keys on your board::

	==> fatload mmc 0:1 <tmpaddr> PK.auth
	==> setenv -e -nv -bs -rt -at -i <tmpaddr>,$filesize PK
	==> fatload mmc 0:1 <tmpaddr> KEK.auth
	==> setenv -e -nv -bs -rt -at -i <tmpaddr>,$filesize KEK
	==> fatload mmc 0:1 <tmpaddr> db.auth
	==> setenv -e -nv -bs -rt -at -i <tmpaddr>,$filesize db

	5. Set up boot parameters on your board::

	==> efidebug boot add 1 HELLO mmc 0:1 /helloworld.efi.signed ""

	Then your board runs that image from Boot manager (See below).
	You can also try this sequence by running Pytest, test_efi_secboot,
	on sandbox::

	$ cd <U-Boot source directory>
	$ pytest.py test/py/tests/test_efi_secboot/test_signed.py --bd sandbox

	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
	* runtime services

	The API can be extended by loading UEFI drivers which come in two variants:

	* boot drivers
	* 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 [5]. 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 [4].

	This driver is only available if U-Boot is configured with::

	CONFIG_BLK=y
	CONFIG_PARTITIONS=y

	Miscellaneous
	-------------

	Load file 2 protocol
	~~~~~~~~~~~~~~~~~~~~

	The load file 2 protocol can be used by the Linux kernel to load the initial
	RAM disk. U-Boot can be configured to provide an implementation with::

	EFI_LOAD_FILE2_INITRD=y
	EFI_INITRD_FILESPEC=interface dev:part path_to_initrd

	Links
	-----

	* [1] http://uefi.org/specifications - UEFI specifications
	* [2] https://github.com/ARM-software/ebbr/releases/download/v1.0/ebbr-v1.0.pdf -
	Embedded Base Boot Requirements (EBBR) Specification - Release v1.0
	* [3] https://developer.arm.com/docs/den0044/latest/server-base-boot-requirements-system-software-on-arm-platforms-version-11 -
	Server Base Boot Requirements System Software on ARM Platforms - Version 1.1
	* [4] :doc:`iscsi`
	* [5] :doc:`../driver-model/index`