This patch provides documentation of the [U]EFI runtime services and configuration features. Cc: linux-doc@xxxxxxxxxxxxxxx Signed-off-by: Leif Lindholm <leif.lindholm@xxxxxxxxxx> Acked-by: Rob Landley <rob@xxxxxxxxxxx> --- Documentation/arm/00-INDEX | 3 +++ Documentation/arm/uefi.txt | 47 ++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 50 insertions(+) create mode 100644 Documentation/arm/uefi.txt diff --git a/Documentation/arm/00-INDEX b/Documentation/arm/00-INDEX index 4978456..87e01d1 100644 --- a/Documentation/arm/00-INDEX +++ b/Documentation/arm/00-INDEX @@ -36,3 +36,6 @@ nwfpe/ - NWFPE floating point emulator documentation swp_emulation - SWP/SWPB emulation handler/logging description + +uefi.txt + - [U]EFI configuration and runtime services documentation diff --git a/Documentation/arm/uefi.txt b/Documentation/arm/uefi.txt new file mode 100644 index 0000000..e6e4d41 --- /dev/null +++ b/Documentation/arm/uefi.txt @@ -0,0 +1,47 @@ +UEFI, the Unified Extensible Firmware Interface is a speifcication +governing the behaviours of compatible firmware interfaces. It is +maintained by the UEFI Forum - http://www.uefi.org/. + +Since UEFI is an evolution of its predecessor 'EFI', the terms EFI and +UEFI are used somewhat interchangeably in this document and associated +source code. + +The implementation depends on receiving the UEFI runtime memory map and a +pointer to the System Table in a Flattened Device Tree - so is only available +with CONFIG_OF. + +It parses the FDT /chosen node for the following parameters: +- 'linux,efi-system-table': + Physical address of the system table. (required) + 64-bit value since an ARMv7 plattform may support LPAE, and to facilitate + code sharing with arm64. Top 32 bits will be ignored, since UEFI specification + mandates a 1:1 mapping of all RAM. +- 'linux,efi-mmap': + The EFI memory map as an embedded property. (required) + An array of type EFI_MEMORY_DESCRIPTOR as described by the UEFI + specification, current version described in Linux by efi_memory_desc_t. + The memory map is represented in little-endian, not DT, byte order. + This map needs to contain at least the regions to be preserved for runtime + services, but would normally just be the map retreieved by calling UEFI + GetMemoryMap() immediately before ExitBootServices(). +- 'linux,efi-mmap-desc-size': + Size of each descriptor in the memory map. (override default) +- 'linux,efi-mmap-desc-ver': + Memory descriptor format version. (override default) + +It also depends on early_memremap() to parse the UEFI configuration tables. + +For actually enabling [U]EFI support, enable: +- CONFIG_EFI=y +- CONFIG_EFI_VARS=y or m + +After the kernel has mapped the required regions into its address space, +a SetVirtualAddressMap() call is made into UEFI in order to update +relocations. This call must be performed with all the code in a 1:1 +mapping. This implementation achieves this by temporarily disabling the +MMU for the duration of this call. This can only be done safely: +- before secondary CPUs are brought online. +- after early_initcalls have completed, since it uses setup_mm_for_reboot(). + +For verbose debug messages, specify 'uefi_debug' on the kernel command +line. -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
