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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
Heinrich Schuchardtdc6f3f42019-04-10 08:04:38 +020017The implementation of UEFI in U-Boot strives to reach the requirements described
18in the "Embedded Base Boot Requirements (EBBR) Specification - Release v1.0"
19[4]. The "Server Base Boot Requirements System Software on ARM Platforms" [5]
20describes a superset of the EBBR specification and may be used as further
21reference.
Heinrich Schuchardt9ba712d2019-03-28 08:09:16 +010022
23A full blown UEFI implementation would contradict the U-Boot design principle
24"keep it small".
25
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +010026## Building for UEFI
27
Heinrich Schuchardt4f3cb4d2018-12-30 12:54:36 +010028The UEFI standard supports only little-endian systems. The UEFI support can be
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +010029activated for ARM and x86 by specifying
30
31 CONFIG_CMD_BOOTEFI=y
32 CONFIG_EFI_LOADER=y
33
34in the .config file.
35
36Support for attaching virtual block devices, e.g. iSCSI drives connected by the
37loaded UEFI application [3], requires
38
39 CONFIG_BLK=y
40 CONFIG_PARTITIONS=y
41
42### Executing a UEFI binary
43
44The bootefi command is used to start UEFI applications or to install UEFI
45drivers. It takes two parameters
46
47 bootefi <image address> [fdt address]
48
49* image address - the memory address of the UEFI binary
50* fdt address - the memory address of the flattened device tree
51
52Below you find the output of an example session starting GRUB.
53
54 => load mmc 0:2 ${fdt_addr_r} boot/dtb
55 29830 bytes read in 14 ms (2 MiB/s)
56 => load mmc 0:1 ${kernel_addr_r} efi/debian/grubaa64.efi
57 reading efi/debian/grubaa64.efi
58 120832 bytes read in 7 ms (16.5 MiB/s)
59 => bootefi ${kernel_addr_r} ${fdt_addr_r}
60
61The environment variable 'bootargs' is passed as load options in the UEFI system
62table. The Linux kernel EFI stub uses the load options as command line
63arguments.
64
65### Executing the boot manager
66
Heinrich Schuchardt4f3cb4d2018-12-30 12:54:36 +010067The UEFI specification foresees to define boot entries and boot sequence via UEFI
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +010068variables. Booting according to these variables is possible via
69
70 bootefi bootmgr [fdt address]
71
72As of U-Boot v2018.03 UEFI variables are not persisted and cannot be set at
73runtime.
74
75### Executing the built in hello world application
76
77A hello world UEFI application can be built with
78
79 CONFIG_CMD_BOOTEFI_HELLO_COMPILE=y
80
81It can be embedded into the U-Boot binary with
82
83 CONFIG_CMD_BOOTEFI_HELLO=y
84
85The bootefi command is used to start the embedded hello world application.
86
87 bootefi hello [fdt address]
88
89Below you find the output of an example session.
90
91 => bootefi hello ${fdtcontroladdr}
92 ## Starting EFI application at 01000000 ...
93 WARNING: using memory device/image path, this may confuse some payloads!
94 Hello, world!
95 Running on UEFI 2.7
96 Have SMBIOS table
97 Have device tree
98 Load options: root=/dev/sdb3 init=/sbin/init rootwait ro
99 ## Application terminated, r = 0
100
101The environment variable fdtcontroladdr points to U-Boot's internal device tree
102(if available).
103
Heinrich Schuchardt4f3cb4d2018-12-30 12:54:36 +0100104### Executing the built-in self-test
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +0100105
Heinrich Schuchardt4f3cb4d2018-12-30 12:54:36 +0100106An UEFI self-test suite can be embedded in U-Boot by building with
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +0100107
108 CONFIG_CMD_BOOTEFI_SELFTEST=y
109
110For testing the UEFI implementation the bootefi command can be used to start the
Heinrich Schuchardt4f3cb4d2018-12-30 12:54:36 +0100111self-test.
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +0100112
113 bootefi selftest [fdt address]
114
115The environment variable 'efi_selftest' can be used to select a single test. If
116it is not provided all tests are executed except those marked as 'on request'.
117If the environment variable is set to 'list' a list of all tests is shown.
118
119Below you can find the output of an example session.
120
121 => setenv efi_selftest simple network protocol
122 => bootefi selftest
123 Testing EFI API implementation
124 Selected test: 'simple network protocol'
125 Setting up 'simple network protocol'
126 Setting up 'simple network protocol' succeeded
127 Executing 'simple network protocol'
128 DHCP Discover
129 DHCP reply received from 192.168.76.2 (52:55:c0:a8:4c:02)
130 as broadcast message.
131 Executing 'simple network protocol' succeeded
132 Tearing down 'simple network protocol'
133 Tearing down 'simple network protocol' succeeded
134 Boot services terminated
135 Summary: 0 failures
136 Preparing for reset. Press any key.
137
138## The UEFI life cycle
139
140After the U-Boot platform has been initialized the UEFI API provides two kinds
141of services
142
143* boot services and
144* runtime services.
145
146The API can be extended by loading UEFI drivers which come in two variants
147
148* boot drivers and
149* runtime drivers.
150
151UEFI drivers are installed with U-Boot's bootefi command. With the same command
152UEFI applications can be executed.
153
154Loaded images of UEFI drivers stay in memory after returning to U-Boot while
155loaded images of applications are removed from memory.
156
157An UEFI application (e.g. an operating system) that wants to take full control
158of the system calls ExitBootServices. After a UEFI application calls
159ExitBootServices
160
161* boot services are not available anymore
162* timer events are stopped
163* the memory used by U-Boot except for runtime services is released
164* the memory used by boot time drivers is released
165
166So this is a point of no return. Afterwards the UEFI application can only return
167to U-Boot by rebooting.
168
169## The UEFI object model
170
171UEFI offers a flexible and expandable object model. The objects in the UEFI API
172are devices, drivers, and loaded images. These objects are referenced by
173handles.
174
175The interfaces implemented by the objects are referred to as protocols. These
176are identified by GUIDs. They can be installed and uninstalled by calling the
177appropriate boot services.
178
179Handles are created by the InstallProtocolInterface or the
180InstallMultipleProtocolinterfaces service if NULL is passed as handle.
181
182Handles are deleted when the last protocol has been removed with the
183UninstallProtocolInterface or the UninstallMultipleProtocolInterfaces service.
184
185Devices offer the EFI_DEVICE_PATH_PROTOCOL. A device path is the concatenation
186of device nodes. By their device paths all devices of a system are arranged in a
187tree.
188
189Drivers offer the EFI_DRIVER_BINDING_PROTOCOL. This protocol is used to connect
190a driver to devices (which are referenced as controllers in this context).
191
192Loaded images offer the EFI_LOADED_IMAGE_PROTOCOL. This protocol provides meta
193information about the image and a pointer to the unload callback function.
194
195## The UEFI events
196
197In the UEFI terminology an event is a data object referencing a notification
198function which is queued for calling when the event is signaled. The following
199types of events exist:
200
201* periodic and single shot timer events
202* exit boot services events, triggered by calling the ExitBootServices() service
203* virtual address change events
204* memory map change events
205* read to boot events
206* reset system events
207* system table events
208* events that are only triggered programmatically
209
210Events can be created with the CreateEvent service and deleted with CloseEvent
211service.
212
213Events can be assigned to an event group. If any of the events in a group is
214signaled, all other events in the group are also set to the signaled state.
215
216## The UEFI driver model
217
218A driver is specific for a single protocol installed on a device. To install a
219driver on a device the ConnectController service is called. In this context
220controller refers to the device for which the driver is installed.
221
222The relevant drivers are identified using the EFI_DRIVER_BINDING_PROTOCOL. This
223protocol has has three functions:
224
225* supported - determines if the driver is compatible with the device
226* start - installs the driver by opening the relevant protocol with
227 attribute EFI_OPEN_PROTOCOL_BY_DRIVER
228* stop - uninstalls the driver
229
230The driver may create child controllers (child devices). E.g. a driver for block
231IO devices will create the device handles for the partitions. The child
232controllers will open the supported protocol with the attribute
233EFI_OPEN_PROTOCOL_BY_CHILD_CONTROLLER.
234
235A driver can be detached from a device using the DisconnectController service.
236
237## U-Boot devices mapped as UEFI devices
238
239Some of the U-Boot devices are mapped as UEFI devices
240
241* block IO devices
242* console
243* graphical output
244* network adapter
245
246As of U-Boot 2018.03 the logic for doing this is hard coded.
247
248The development target is to integrate the setup of these UEFI devices with the
249U-Boot driver model. So when a U-Boot device is discovered a handle should be
250created and the device path protocol and the relevant IO protocol should be
251installed. The UEFI driver then would be attached by calling ConnectController.
252When a U-Boot device is removed DisconnectController should be called.
253
254## UEFI devices mapped as U-Boot devices
255
256UEFI drivers binaries and applications may create new (virtual) devices, install
257a protocol and call the ConnectController service. Now the matching UEFI driver
258is determined by iterating over the implementations of the
259EFI_DRIVER_BINDING_PROTOCOL.
260
261It is the task of the UEFI driver to create a corresponding U-Boot device and to
262proxy calls for this U-Boot device to the controller.
263
264In U-Boot 2018.03 this has only been implemented for block IO devices.
265
266### UEFI uclass
267
268An UEFI uclass driver (lib/efi_driver/efi_uclass.c) has been created that
269takes care of initializing the UEFI drivers and providing the
270EFI_DRIVER_BINDING_PROTOCOL implementation for the UEFI drivers.
271
272A linker created list is used to keep track of the UEFI drivers. To create an
273entry in the list the UEFI driver uses the U_BOOT_DRIVER macro specifying
274UCLASS_EFI as the ID of its uclass, e.g.
275
276 /* Identify as UEFI driver */
277 U_BOOT_DRIVER(efi_block) = {
278 .name = "EFI block driver",
279 .id = UCLASS_EFI,
280 .ops = &driver_ops,
281 };
282
283The available operations are defined via the structure struct efi_driver_ops.
284
285 struct efi_driver_ops {
286 const efi_guid_t *protocol;
287 const efi_guid_t *child_protocol;
288 int (*bind)(efi_handle_t handle, void *interface);
289 };
290
291When the supported() function of the EFI_DRIVER_BINDING_PROTOCOL is called the
292uclass checks if the protocol GUID matches the protocol GUID of the UEFI driver.
293In the start() function the bind() function of the UEFI driver is called after
294checking the GUID.
295The stop() function of the EFI_DRIVER_BINDING_PROTOCOL disconnects the child
296controllers created by the UEFI driver and the UEFI driver. (In U-Boot v2013.03
297this is not yet completely implemented.)
298
299### UEFI block IO driver
300
301The UEFI block IO driver supports devices exposing the EFI_BLOCK_IO_PROTOCOL.
302
303When connected it creates a new U-Boot block IO device with interface type
304IF_TYPE_EFI, adds child controllers mapping the partitions, and installs the
305EFI_SIMPLE_FILE_SYSTEM_PROTOCOL on these. This can be used together with the
306software iPXE to boot from iSCSI network drives [3].
307
308This driver is only available if U-Boot is configured with
309
310 CONFIG_BLK=y
311 CONFIG_PARTITIONS=y
312
Heinrich Schuchardt98dc2602019-03-27 22:02:30 +0100313## TODOs as of U-Boot 2019.04
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +0100314
315* unimplemented or incompletely implemented boot services
316 * Exit - call unload function, unload applications only
Heinrich Schuchardt71cee4c2018-05-12 03:28:44 +0200317 * ProtocolRegisterNotify
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +0100318 * UnloadImage
319
Heinrich Schuchardt71cee4c2018-05-12 03:28:44 +0200320* unimplemented or incompletely implemented runtime services
321 * SetVariable() ignores attribute EFI_VARIABLE_APPEND_WRITE
Heinrich Schuchardt71cee4c2018-05-12 03:28:44 +0200322 * QueryVariableInfo is not implemented
323
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +0100324* unimplemented events
325 * EVT_RUNTIME
326 * EVT_SIGNAL_VIRTUAL_ADDRESS_CHANGE
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +0100327
328* data model
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +0100329 * manage configuration tables in a linked list
330
331* UEFI drivers
332 * support DisconnectController for UEFI block devices.
333
334* support for CONFIG_EFI_LOADER in the sandbox (CONFIG_SANDBOX=y)
335
336* UEFI variables
337 * persistence
338 * runtime support
339
Heinrich Schuchardt17394f92019-03-27 21:41:04 +0100340* incompletely implemented protocols
341 * support version 0x00020000 of the EFI file protocol
342
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +0100343## Links
344
345* [1](http://uefi.org/specifications)
346 http://uefi.org/specifications - UEFI specifications
347* [2](./driver-model/README.txt) doc/driver-model/README.txt - Driver model
348* [3](./README.iscsi) doc/README.iscsi - iSCSI booting with U-Boot and iPXE
Heinrich Schuchardtdc6f3f42019-04-10 08:04:38 +0200349* [4](https://github.com/ARM-software/ebbr/releases/download/v1.0/ebbr-v1.0.pdf)
350 Embedded Base Boot Requirements (EBBR) Specification - Release v1.0
351* [5](https://developer.arm.com/docs/den0044/latest/server-base-boot-requirements-system-software-on-arm-platforms-version-11)
Heinrich Schuchardt9ba712d2019-03-28 08:09:16 +0100352 Server Base Boot Requirements System Software on ARM Platforms - Version 1.1