doc: integrate UEFI documentation into Sphinx toctree

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>

4 files changed, 764 insertions, 0 deletions

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..51d38cde24
--- /dev/null
+++ b/doc/uefi/iscsi.rst
@@ -0,0 +1,184 @@
+.. 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:
+
+.. code-block:: c
+
+    /* 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:
+
+.. code-block:: c
+
+    /* 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 in the configuration file [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..c9a41bc919
--- /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..db942df694
--- /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"
+[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.
+
+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
+
+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`