projects / people / ms / linux.git / blame
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|---|---|---|
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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: | |
| dc7a12bd MCC |
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. | |
| 6329d73d HS |
67 | |
| 68 | linux,initrd-start 64-bit Physical start address of an initrd | |
| 69 | ||
| 70 | linux,initrd-end 64-bit Physical end address of an initrd | |
| 71 | ||
| 72 | kaslr-seed 64-bit Entropy used to randomize the kernel image | |
| 73 | base address location. | |
| dc7a12bd | 74 | ========================== ====== =========================================== |