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Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +01001<!--
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Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +01003
Tom Rinif739fcd2018-05-07 17:02:21 -04004Copyright (c) 2018 Heinrich Schuchardt
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +01005-->
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
15## Building for UEFI
16
17The UEFI standard supports only little endian systems. The UEFI support can be
18activated for ARM and x86 by specifying
19
20 CONFIG_CMD_BOOTEFI=y
21 CONFIG_EFI_LOADER=y
22
23in the .config file.
24
25Support for attaching virtual block devices, e.g. iSCSI drives connected by the
26loaded UEFI application [3], requires
27
28 CONFIG_BLK=y
29 CONFIG_PARTITIONS=y
30
31### Executing a UEFI binary
32
33The bootefi command is used to start UEFI applications or to install UEFI
34drivers. It takes two parameters
35
36 bootefi <image address> [fdt address]
37
38* image address - the memory address of the UEFI binary
39* fdt address - the memory address of the flattened device tree
40
41Below you find the output of an example session starting GRUB.
42
43 => load mmc 0:2 ${fdt_addr_r} boot/dtb
44 29830 bytes read in 14 ms (2 MiB/s)
45 => load mmc 0:1 ${kernel_addr_r} efi/debian/grubaa64.efi
46 reading efi/debian/grubaa64.efi
47 120832 bytes read in 7 ms (16.5 MiB/s)
48 => bootefi ${kernel_addr_r} ${fdt_addr_r}
49
50The environment variable 'bootargs' is passed as load options in the UEFI system
51table. The Linux kernel EFI stub uses the load options as command line
52arguments.
53
54### Executing the boot manager
55
56The UEFI specfication foresees to define boot entries and boot sequence via UEFI
57variables. Booting according to these variables is possible via
58
59 bootefi bootmgr [fdt address]
60
61As of U-Boot v2018.03 UEFI variables are not persisted and cannot be set at
62runtime.
63
64### Executing the built in hello world application
65
66A hello world UEFI application can be built with
67
68 CONFIG_CMD_BOOTEFI_HELLO_COMPILE=y
69
70It can be embedded into the U-Boot binary with
71
72 CONFIG_CMD_BOOTEFI_HELLO=y
73
74The bootefi command is used to start the embedded hello world application.
75
76 bootefi hello [fdt address]
77
78Below you find the output of an example session.
79
80 => bootefi hello ${fdtcontroladdr}
81 ## Starting EFI application at 01000000 ...
82 WARNING: using memory device/image path, this may confuse some payloads!
83 Hello, world!
84 Running on UEFI 2.7
85 Have SMBIOS table
86 Have device tree
87 Load options: root=/dev/sdb3 init=/sbin/init rootwait ro
88 ## Application terminated, r = 0
89
90The environment variable fdtcontroladdr points to U-Boot's internal device tree
91(if available).
92
93### Executing the built-in selftest
94
95An UEFI selftest suite can be embedded in U-Boot by building with
96
97 CONFIG_CMD_BOOTEFI_SELFTEST=y
98
99For testing the UEFI implementation the bootefi command can be used to start the
100selftest.
101
102 bootefi selftest [fdt address]
103
104The environment variable 'efi_selftest' can be used to select a single test. If
105it is not provided all tests are executed except those marked as 'on request'.
106If the environment variable is set to 'list' a list of all tests is shown.
107
108Below you can find the output of an example session.
109
110 => setenv efi_selftest simple network protocol
111 => bootefi selftest
112 Testing EFI API implementation
113 Selected test: 'simple network protocol'
114 Setting up 'simple network protocol'
115 Setting up 'simple network protocol' succeeded
116 Executing 'simple network protocol'
117 DHCP Discover
118 DHCP reply received from 192.168.76.2 (52:55:c0:a8:4c:02)
119 as broadcast message.
120 Executing 'simple network protocol' succeeded
121 Tearing down 'simple network protocol'
122 Tearing down 'simple network protocol' succeeded
123 Boot services terminated
124 Summary: 0 failures
125 Preparing for reset. Press any key.
126
127## The UEFI life cycle
128
129After the U-Boot platform has been initialized the UEFI API provides two kinds
130of services
131
132* boot services and
133* runtime services.
134
135The API can be extended by loading UEFI drivers which come in two variants
136
137* boot drivers and
138* runtime drivers.
139
140UEFI drivers are installed with U-Boot's bootefi command. With the same command
141UEFI applications can be executed.
142
143Loaded images of UEFI drivers stay in memory after returning to U-Boot while
144loaded images of applications are removed from memory.
145
146An UEFI application (e.g. an operating system) that wants to take full control
147of the system calls ExitBootServices. After a UEFI application calls
148ExitBootServices
149
150* boot services are not available anymore
151* timer events are stopped
152* the memory used by U-Boot except for runtime services is released
153* the memory used by boot time drivers is released
154
155So this is a point of no return. Afterwards the UEFI application can only return
156to U-Boot by rebooting.
157
158## The UEFI object model
159
160UEFI offers a flexible and expandable object model. The objects in the UEFI API
161are devices, drivers, and loaded images. These objects are referenced by
162handles.
163
164The interfaces implemented by the objects are referred to as protocols. These
165are identified by GUIDs. They can be installed and uninstalled by calling the
166appropriate boot services.
167
168Handles are created by the InstallProtocolInterface or the
169InstallMultipleProtocolinterfaces service if NULL is passed as handle.
170
171Handles are deleted when the last protocol has been removed with the
172UninstallProtocolInterface or the UninstallMultipleProtocolInterfaces service.
173
174Devices offer the EFI_DEVICE_PATH_PROTOCOL. A device path is the concatenation
175of device nodes. By their device paths all devices of a system are arranged in a
176tree.
177
178Drivers offer the EFI_DRIVER_BINDING_PROTOCOL. This protocol is used to connect
179a driver to devices (which are referenced as controllers in this context).
180
181Loaded images offer the EFI_LOADED_IMAGE_PROTOCOL. This protocol provides meta
182information about the image and a pointer to the unload callback function.
183
184## The UEFI events
185
186In the UEFI terminology an event is a data object referencing a notification
187function which is queued for calling when the event is signaled. The following
188types of events exist:
189
190* periodic and single shot timer events
191* exit boot services events, triggered by calling the ExitBootServices() service
192* virtual address change events
193* memory map change events
194* read to boot events
195* reset system events
196* system table events
197* events that are only triggered programmatically
198
199Events can be created with the CreateEvent service and deleted with CloseEvent
200service.
201
202Events can be assigned to an event group. If any of the events in a group is
203signaled, all other events in the group are also set to the signaled state.
204
205## The UEFI driver model
206
207A driver is specific for a single protocol installed on a device. To install a
208driver on a device the ConnectController service is called. In this context
209controller refers to the device for which the driver is installed.
210
211The relevant drivers are identified using the EFI_DRIVER_BINDING_PROTOCOL. This
212protocol has has three functions:
213
214* supported - determines if the driver is compatible with the device
215* start - installs the driver by opening the relevant protocol with
216 attribute EFI_OPEN_PROTOCOL_BY_DRIVER
217* stop - uninstalls the driver
218
219The driver may create child controllers (child devices). E.g. a driver for block
220IO devices will create the device handles for the partitions. The child
221controllers will open the supported protocol with the attribute
222EFI_OPEN_PROTOCOL_BY_CHILD_CONTROLLER.
223
224A driver can be detached from a device using the DisconnectController service.
225
226## U-Boot devices mapped as UEFI devices
227
228Some of the U-Boot devices are mapped as UEFI devices
229
230* block IO devices
231* console
232* graphical output
233* network adapter
234
235As of U-Boot 2018.03 the logic for doing this is hard coded.
236
237The development target is to integrate the setup of these UEFI devices with the
238U-Boot driver model. So when a U-Boot device is discovered a handle should be
239created and the device path protocol and the relevant IO protocol should be
240installed. The UEFI driver then would be attached by calling ConnectController.
241When a U-Boot device is removed DisconnectController should be called.
242
243## UEFI devices mapped as U-Boot devices
244
245UEFI drivers binaries and applications may create new (virtual) devices, install
246a protocol and call the ConnectController service. Now the matching UEFI driver
247is determined by iterating over the implementations of the
248EFI_DRIVER_BINDING_PROTOCOL.
249
250It is the task of the UEFI driver to create a corresponding U-Boot device and to
251proxy calls for this U-Boot device to the controller.
252
253In U-Boot 2018.03 this has only been implemented for block IO devices.
254
255### UEFI uclass
256
257An UEFI uclass driver (lib/efi_driver/efi_uclass.c) has been created that
258takes care of initializing the UEFI drivers and providing the
259EFI_DRIVER_BINDING_PROTOCOL implementation for the UEFI drivers.
260
261A linker created list is used to keep track of the UEFI drivers. To create an
262entry in the list the UEFI driver uses the U_BOOT_DRIVER macro specifying
263UCLASS_EFI as the ID of its uclass, e.g.
264
265 /* Identify as UEFI driver */
266 U_BOOT_DRIVER(efi_block) = {
267 .name = "EFI block driver",
268 .id = UCLASS_EFI,
269 .ops = &driver_ops,
270 };
271
272The available operations are defined via the structure struct efi_driver_ops.
273
274 struct efi_driver_ops {
275 const efi_guid_t *protocol;
276 const efi_guid_t *child_protocol;
277 int (*bind)(efi_handle_t handle, void *interface);
278 };
279
280When the supported() function of the EFI_DRIVER_BINDING_PROTOCOL is called the
281uclass checks if the protocol GUID matches the protocol GUID of the UEFI driver.
282In the start() function the bind() function of the UEFI driver is called after
283checking the GUID.
284The stop() function of the EFI_DRIVER_BINDING_PROTOCOL disconnects the child
285controllers created by the UEFI driver and the UEFI driver. (In U-Boot v2013.03
286this is not yet completely implemented.)
287
288### UEFI block IO driver
289
290The UEFI block IO driver supports devices exposing the EFI_BLOCK_IO_PROTOCOL.
291
292When connected it creates a new U-Boot block IO device with interface type
293IF_TYPE_EFI, adds child controllers mapping the partitions, and installs the
294EFI_SIMPLE_FILE_SYSTEM_PROTOCOL on these. This can be used together with the
295software iPXE to boot from iSCSI network drives [3].
296
297This driver is only available if U-Boot is configured with
298
299 CONFIG_BLK=y
300 CONFIG_PARTITIONS=y
301
302## TODOs as of U-Boot 2018.03
303
304* unimplemented or incompletely implemented boot services
305 * Exit - call unload function, unload applications only
306 * ReinstallProtocolInterface
307 * UnloadImage
308
309* unimplemented events
310 * EVT_RUNTIME
311 * EVT_SIGNAL_VIRTUAL_ADDRESS_CHANGE
312 * event groups
313
314* data model
315 * manage events in a linked list
316 * manage configuration tables in a linked list
317
318* UEFI drivers
319 * support DisconnectController for UEFI block devices.
320
321* support for CONFIG_EFI_LOADER in the sandbox (CONFIG_SANDBOX=y)
322
323* UEFI variables
324 * persistence
325 * runtime support
326
Heinrich Schuchardtc5249972018-04-11 00:41:52 +0200327* support bootefi booting ARMv7 in non-secure mode (CONFIG_ARMV7_NONSEC=y)
328
Heinrich Schuchardt1914e5b2018-03-02 19:58:50 +0100329## Links
330
331* [1](http://uefi.org/specifications)
332 http://uefi.org/specifications - UEFI specifications
333* [2](./driver-model/README.txt) doc/driver-model/README.txt - Driver model
334* [3](./README.iscsi) doc/README.iscsi - iSCSI booting with U-Boot and iPXE