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6
7# UEFI on U-Boot
8
9The Unified Extensible Firmware Interface Specification (UEFI) [1] has become
10the default for booting on AArch64 and x86 systems. It provides a stable API for
11the interaction of drivers and applications with the firmware. The API comprises
12access to block storage, network, and console to name a few. The Linux kernel
13and boot loaders like GRUB or the FreeBSD loader can be executed.
14
Heinrich Schuchardt9ba712d2019-03-28 08:09:16 +010015## Development target
16
17The implementation of UEFI in U-Boot strives to reach the minimum requirements
18described in "Server Base Boot Requirements System Software on ARM Platforms -
19Version 1.1" [4].
20
21A full blown UEFI implementation would contradict the U-Boot design principle
22"keep it small".
23
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +010024## Building for UEFI
25
Heinrich Schuchardt4f3cb4d2018-12-30 12:54:36 +010026The UEFI standard supports only little-endian systems. The UEFI support can be
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +010027activated for ARM and x86 by specifying
28
29 CONFIG_CMD_BOOTEFI=y
30 CONFIG_EFI_LOADER=y
31
32in the .config file.
33
34Support for attaching virtual block devices, e.g. iSCSI drives connected by the
35loaded UEFI application [3], requires
36
37 CONFIG_BLK=y
38 CONFIG_PARTITIONS=y
39
40### Executing a UEFI binary
41
42The bootefi command is used to start UEFI applications or to install UEFI
43drivers. It takes two parameters
44
45 bootefi <image address> [fdt address]
46
47* image address - the memory address of the UEFI binary
48* fdt address - the memory address of the flattened device tree
49
50Below you find the output of an example session starting GRUB.
51
52 => load mmc 0:2 ${fdt_addr_r} boot/dtb
53 29830 bytes read in 14 ms (2 MiB/s)
54 => load mmc 0:1 ${kernel_addr_r} efi/debian/grubaa64.efi
55 reading efi/debian/grubaa64.efi
56 120832 bytes read in 7 ms (16.5 MiB/s)
57 => bootefi ${kernel_addr_r} ${fdt_addr_r}
58
59The environment variable 'bootargs' is passed as load options in the UEFI system
60table. The Linux kernel EFI stub uses the load options as command line
61arguments.
62
63### Executing the boot manager
64
Heinrich Schuchardt4f3cb4d2018-12-30 12:54:36 +010065The UEFI specification foresees to define boot entries and boot sequence via UEFI
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +010066variables. Booting according to these variables is possible via
67
68 bootefi bootmgr [fdt address]
69
70As of U-Boot v2018.03 UEFI variables are not persisted and cannot be set at
71runtime.
72
73### Executing the built in hello world application
74
75A hello world UEFI application can be built with
76
77 CONFIG_CMD_BOOTEFI_HELLO_COMPILE=y
78
79It can be embedded into the U-Boot binary with
80
81 CONFIG_CMD_BOOTEFI_HELLO=y
82
83The bootefi command is used to start the embedded hello world application.
84
85 bootefi hello [fdt address]
86
87Below you find the output of an example session.
88
89 => bootefi hello ${fdtcontroladdr}
90 ## Starting EFI application at 01000000 ...
91 WARNING: using memory device/image path, this may confuse some payloads!
92 Hello, world!
93 Running on UEFI 2.7
94 Have SMBIOS table
95 Have device tree
96 Load options: root=/dev/sdb3 init=/sbin/init rootwait ro
97 ## Application terminated, r = 0
98
99The environment variable fdtcontroladdr points to U-Boot's internal device tree
100(if available).
101
Heinrich Schuchardt4f3cb4d2018-12-30 12:54:36 +0100102### Executing the built-in self-test
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +0100103
Heinrich Schuchardt4f3cb4d2018-12-30 12:54:36 +0100104An UEFI self-test suite can be embedded in U-Boot by building with
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +0100105
106 CONFIG_CMD_BOOTEFI_SELFTEST=y
107
108For testing the UEFI implementation the bootefi command can be used to start the
Heinrich Schuchardt4f3cb4d2018-12-30 12:54:36 +0100109self-test.
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +0100110
111 bootefi selftest [fdt address]
112
113The environment variable 'efi_selftest' can be used to select a single test. If
114it is not provided all tests are executed except those marked as 'on request'.
115If the environment variable is set to 'list' a list of all tests is shown.
116
117Below you can find the output of an example session.
118
119 => setenv efi_selftest simple network protocol
120 => bootefi selftest
121 Testing EFI API implementation
122 Selected test: 'simple network protocol'
123 Setting up 'simple network protocol'
124 Setting up 'simple network protocol' succeeded
125 Executing 'simple network protocol'
126 DHCP Discover
127 DHCP reply received from 192.168.76.2 (52:55:c0:a8:4c:02)
128 as broadcast message.
129 Executing 'simple network protocol' succeeded
130 Tearing down 'simple network protocol'
131 Tearing down 'simple network protocol' succeeded
132 Boot services terminated
133 Summary: 0 failures
134 Preparing for reset. Press any key.
135
136## The UEFI life cycle
137
138After the U-Boot platform has been initialized the UEFI API provides two kinds
139of services
140
141* boot services and
142* runtime services.
143
144The API can be extended by loading UEFI drivers which come in two variants
145
146* boot drivers and
147* runtime drivers.
148
149UEFI drivers are installed with U-Boot's bootefi command. With the same command
150UEFI applications can be executed.
151
152Loaded images of UEFI drivers stay in memory after returning to U-Boot while
153loaded images of applications are removed from memory.
154
155An UEFI application (e.g. an operating system) that wants to take full control
156of the system calls ExitBootServices. After a UEFI application calls
157ExitBootServices
158
159* boot services are not available anymore
160* timer events are stopped
161* the memory used by U-Boot except for runtime services is released
162* the memory used by boot time drivers is released
163
164So this is a point of no return. Afterwards the UEFI application can only return
165to U-Boot by rebooting.
166
167## The UEFI object model
168
169UEFI offers a flexible and expandable object model. The objects in the UEFI API
170are devices, drivers, and loaded images. These objects are referenced by
171handles.
172
173The interfaces implemented by the objects are referred to as protocols. These
174are identified by GUIDs. They can be installed and uninstalled by calling the
175appropriate boot services.
176
177Handles are created by the InstallProtocolInterface or the
178InstallMultipleProtocolinterfaces service if NULL is passed as handle.
179
180Handles are deleted when the last protocol has been removed with the
181UninstallProtocolInterface or the UninstallMultipleProtocolInterfaces service.
182
183Devices offer the EFI_DEVICE_PATH_PROTOCOL. A device path is the concatenation
184of device nodes. By their device paths all devices of a system are arranged in a
185tree.
186
187Drivers offer the EFI_DRIVER_BINDING_PROTOCOL. This protocol is used to connect
188a driver to devices (which are referenced as controllers in this context).
189
190Loaded images offer the EFI_LOADED_IMAGE_PROTOCOL. This protocol provides meta
191information about the image and a pointer to the unload callback function.
192
193## The UEFI events
194
195In the UEFI terminology an event is a data object referencing a notification
196function which is queued for calling when the event is signaled. The following
197types of events exist:
198
199* periodic and single shot timer events
200* exit boot services events, triggered by calling the ExitBootServices() service
201* virtual address change events
202* memory map change events
203* read to boot events
204* reset system events
205* system table events
206* events that are only triggered programmatically
207
208Events can be created with the CreateEvent service and deleted with CloseEvent
209service.
210
211Events can be assigned to an event group. If any of the events in a group is
212signaled, all other events in the group are also set to the signaled state.
213
214## The UEFI driver model
215
216A driver is specific for a single protocol installed on a device. To install a
217driver on a device the ConnectController service is called. In this context
218controller refers to the device for which the driver is installed.
219
220The relevant drivers are identified using the EFI_DRIVER_BINDING_PROTOCOL. This
221protocol has has three functions:
222
223* supported - determines if the driver is compatible with the device
224* start - installs the driver by opening the relevant protocol with
225 attribute EFI_OPEN_PROTOCOL_BY_DRIVER
226* stop - uninstalls the driver
227
228The driver may create child controllers (child devices). E.g. a driver for block
229IO devices will create the device handles for the partitions. The child
230controllers will open the supported protocol with the attribute
231EFI_OPEN_PROTOCOL_BY_CHILD_CONTROLLER.
232
233A driver can be detached from a device using the DisconnectController service.
234
235## U-Boot devices mapped as UEFI devices
236
237Some of the U-Boot devices are mapped as UEFI devices
238
239* block IO devices
240* console
241* graphical output
242* network adapter
243
244As of U-Boot 2018.03 the logic for doing this is hard coded.
245
246The development target is to integrate the setup of these UEFI devices with the
247U-Boot driver model. So when a U-Boot device is discovered a handle should be
248created and the device path protocol and the relevant IO protocol should be
249installed. The UEFI driver then would be attached by calling ConnectController.
250When a U-Boot device is removed DisconnectController should be called.
251
252## UEFI devices mapped as U-Boot devices
253
254UEFI drivers binaries and applications may create new (virtual) devices, install
255a protocol and call the ConnectController service. Now the matching UEFI driver
256is determined by iterating over the implementations of the
257EFI_DRIVER_BINDING_PROTOCOL.
258
259It is the task of the UEFI driver to create a corresponding U-Boot device and to
260proxy calls for this U-Boot device to the controller.
261
262In U-Boot 2018.03 this has only been implemented for block IO devices.
263
264### UEFI uclass
265
266An UEFI uclass driver (lib/efi_driver/efi_uclass.c) has been created that
267takes care of initializing the UEFI drivers and providing the
268EFI_DRIVER_BINDING_PROTOCOL implementation for the UEFI drivers.
269
270A linker created list is used to keep track of the UEFI drivers. To create an
271entry in the list the UEFI driver uses the U_BOOT_DRIVER macro specifying
272UCLASS_EFI as the ID of its uclass, e.g.
273
274 /* Identify as UEFI driver */
275 U_BOOT_DRIVER(efi_block) = {
276 .name = "EFI block driver",
277 .id = UCLASS_EFI,
278 .ops = &driver_ops,
279 };
280
281The available operations are defined via the structure struct efi_driver_ops.
282
283 struct efi_driver_ops {
284 const efi_guid_t *protocol;
285 const efi_guid_t *child_protocol;
286 int (*bind)(efi_handle_t handle, void *interface);
287 };
288
289When the supported() function of the EFI_DRIVER_BINDING_PROTOCOL is called the
290uclass checks if the protocol GUID matches the protocol GUID of the UEFI driver.
291In the start() function the bind() function of the UEFI driver is called after
292checking the GUID.
293The stop() function of the EFI_DRIVER_BINDING_PROTOCOL disconnects the child
294controllers created by the UEFI driver and the UEFI driver. (In U-Boot v2013.03
295this is not yet completely implemented.)
296
297### UEFI block IO driver
298
299The UEFI block IO driver supports devices exposing the EFI_BLOCK_IO_PROTOCOL.
300
301When connected it creates a new U-Boot block IO device with interface type
302IF_TYPE_EFI, adds child controllers mapping the partitions, and installs the
303EFI_SIMPLE_FILE_SYSTEM_PROTOCOL on these. This can be used together with the
304software iPXE to boot from iSCSI network drives [3].
305
306This driver is only available if U-Boot is configured with
307
308 CONFIG_BLK=y
309 CONFIG_PARTITIONS=y
310
Heinrich Schuchardt98dc2602019-03-27 22:02:30 +0100311## TODOs as of U-Boot 2019.04
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +0100312
313* unimplemented or incompletely implemented boot services
314 * Exit - call unload function, unload applications only
Heinrich Schuchardt71cee4c2018-05-12 03:28:44 +0200315 * ProtocolRegisterNotify
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +0100316 * UnloadImage
317
Heinrich Schuchardt71cee4c2018-05-12 03:28:44 +0200318* unimplemented or incompletely implemented runtime services
319 * SetVariable() ignores attribute EFI_VARIABLE_APPEND_WRITE
Heinrich Schuchardt71cee4c2018-05-12 03:28:44 +0200320 * QueryVariableInfo is not implemented
321
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +0100322* unimplemented events
323 * EVT_RUNTIME
324 * EVT_SIGNAL_VIRTUAL_ADDRESS_CHANGE
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +0100325
326* data model
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +0100327 * manage configuration tables in a linked list
328
329* UEFI drivers
330 * support DisconnectController for UEFI block devices.
331
332* support for CONFIG_EFI_LOADER in the sandbox (CONFIG_SANDBOX=y)
333
334* UEFI variables
335 * persistence
336 * runtime support
337
Heinrich Schuchardt17394f92019-03-27 21:41:04 +0100338* incompletely implemented protocols
339 * support version 0x00020000 of the EFI file protocol
340
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +0100341## Links
342
343* [1](http://uefi.org/specifications)
344 http://uefi.org/specifications - UEFI specifications
345* [2](./driver-model/README.txt) doc/driver-model/README.txt - Driver model
346* [3](./README.iscsi) doc/README.iscsi - iSCSI booting with U-Boot and iPXE
Heinrich Schuchardt9ba712d2019-03-28 08:09:16 +0100347* [4](https://developer.arm.com/docs/den0044/latest/server-base-boot-requirements-system-software-on-arm-platforms-version-11)
348 Server Base Boot Requirements System Software on ARM Platforms - Version 1.1