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1 | ================================================ |
2 | The Unified Extensible Firmware Interface (UEFI) | |
3 | ================================================ | |
4 | ||
e1977464 LL |
5 | UEFI, the Unified Extensible Firmware Interface, is a specification |
6 | governing the behaviours of compatible firmware interfaces. It is | |
7 | maintained by the UEFI Forum - http://www.uefi.org/. | |
8 | ||
9 | UEFI is an evolution of its predecessor 'EFI', so the terms EFI and | |
10 | UEFI are used somewhat interchangeably in this document and associated | |
11 | source code. As a rule, anything new uses 'UEFI', whereas 'EFI' refers | |
12 | to legacy code or specifications. | |
13 | ||
14 | UEFI support in Linux | |
15 | ===================== | |
16 | Booting on a platform with firmware compliant with the UEFI specification | |
17 | makes it possible for the kernel to support additional features: | |
dc7a12bd | 18 | |
e1977464 LL |
19 | - UEFI Runtime Services |
20 | - Retrieving various configuration information through the standardised | |
21 | interface of UEFI configuration tables. (ACPI, SMBIOS, ...) | |
22 | ||
23 | For actually enabling [U]EFI support, enable: | |
dc7a12bd | 24 | |
e1977464 | 25 | - CONFIG_EFI=y |
963fabf3 | 26 | - CONFIG_EFIVAR_FS=y or m |
e1977464 LL |
27 | |
28 | The implementation depends on receiving information about the UEFI environment | |
29 | in a Flattened Device Tree (FDT) - so is only available with CONFIG_OF. | |
30 | ||
31 | UEFI stub | |
32 | ========= | |
33 | The "stub" is a feature that extends the Image/zImage into a valid UEFI | |
34 | PE/COFF executable, including a loader application that makes it possible to | |
35 | load the kernel directly from the UEFI shell, boot menu, or one of the | |
36 | lightweight bootloaders like Gummiboot or rEFInd. | |
37 | ||
38 | The kernel image built with stub support remains a valid kernel image for | |
39 | booting in non-UEFI environments. | |
40 | ||
41 | UEFI kernel support on ARM | |
42 | ========================== | |
43 | UEFI kernel support on the ARM architectures (arm and arm64) is only available | |
44 | when boot is performed through the stub. | |
45 | ||
46 | When booting in UEFI mode, the stub deletes any memory nodes from a provided DT. | |
47 | Instead, the kernel reads the UEFI memory map. | |
48 | ||
49 | The stub populates the FDT /chosen node with (and the kernel scans for) the | |
50 | following parameters: | |
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51 | |
52 | ========================== ====== =========================================== | |
53 | Name Size Description | |
54 | ========================== ====== =========================================== | |
55 | linux,uefi-system-table 64-bit Physical address of the UEFI System Table. | |
56 | ||
57 | linux,uefi-mmap-start 64-bit Physical address of the UEFI memory map, | |
58 | populated by the UEFI GetMemoryMap() call. | |
59 | ||
60 | linux,uefi-mmap-size 32-bit Size in bytes of the UEFI memory map | |
61 | pointed to in previous entry. | |
62 | ||
63 | linux,uefi-mmap-desc-size 32-bit Size in bytes of each entry in the UEFI | |
64 | memory map. | |
65 | ||
66 | linux,uefi-mmap-desc-ver 32-bit Version of the mmap descriptor format. | |
67 | ========================== ====== =========================================== |