diff options
author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
---|---|---|
committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/arm/uefi.rst | |
parent | Initial commit. (diff) | |
download | linux-upstream/5.10.209.tar.xz linux-upstream/5.10.209.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | Documentation/arm/uefi.rst | 67 |
1 files changed, 67 insertions, 0 deletions
diff --git a/Documentation/arm/uefi.rst b/Documentation/arm/uefi.rst new file mode 100644 index 000000000..f732f9574 --- /dev/null +++ b/Documentation/arm/uefi.rst @@ -0,0 +1,67 @@ +================================================ +The Unified Extensible Firmware Interface (UEFI) +================================================ + +UEFI, the Unified Extensible Firmware Interface, is a specification +governing the behaviours of compatible firmware interfaces. It is +maintained by the UEFI Forum - http://www.uefi.org/. + +UEFI is an evolution of its predecessor 'EFI', so the terms EFI and +UEFI are used somewhat interchangeably in this document and associated +source code. As a rule, anything new uses 'UEFI', whereas 'EFI' refers +to legacy code or specifications. + +UEFI support in Linux +===================== +Booting on a platform with firmware compliant with the UEFI specification +makes it possible for the kernel to support additional features: + +- UEFI Runtime Services +- Retrieving various configuration information through the standardised + interface of UEFI configuration tables. (ACPI, SMBIOS, ...) + +For actually enabling [U]EFI support, enable: + +- CONFIG_EFI=y +- CONFIG_EFIVAR_FS=y or m + +The implementation depends on receiving information about the UEFI environment +in a Flattened Device Tree (FDT) - so is only available with CONFIG_OF. + +UEFI stub +========= +The "stub" is a feature that extends the Image/zImage into a valid UEFI +PE/COFF executable, including a loader application that makes it possible to +load the kernel directly from the UEFI shell, boot menu, or one of the +lightweight bootloaders like Gummiboot or rEFInd. + +The kernel image built with stub support remains a valid kernel image for +booting in non-UEFI environments. + +UEFI kernel support on ARM +========================== +UEFI kernel support on the ARM architectures (arm and arm64) is only available +when boot is performed through the stub. + +When booting in UEFI mode, the stub deletes any memory nodes from a provided DT. +Instead, the kernel reads the UEFI memory map. + +The stub populates the FDT /chosen node with (and the kernel scans for) the +following parameters: + +========================== ====== =========================================== +Name Size Description +========================== ====== =========================================== +linux,uefi-system-table 64-bit Physical address of the UEFI System Table. + +linux,uefi-mmap-start 64-bit Physical address of the UEFI memory map, + populated by the UEFI GetMemoryMap() call. + +linux,uefi-mmap-size 32-bit Size in bytes of the UEFI memory map + pointed to in previous entry. + +linux,uefi-mmap-desc-size 32-bit Size in bytes of each entry in the UEFI + memory map. + +linux,uefi-mmap-desc-ver 32-bit Version of the mmap descriptor format. +========================== ====== =========================================== |