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Documentation / arm / uefi.txt




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Based on kernel version 3.16. Page generated on 2014-08-06 21:36 EST.

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