1*4882a593Smuzhiyun================================================ 2*4882a593SmuzhiyunThe Unified Extensible Firmware Interface (UEFI) 3*4882a593Smuzhiyun================================================ 4*4882a593Smuzhiyun 5*4882a593SmuzhiyunUEFI, the Unified Extensible Firmware Interface, is a specification 6*4882a593Smuzhiyungoverning the behaviours of compatible firmware interfaces. It is 7*4882a593Smuzhiyunmaintained by the UEFI Forum - http://www.uefi.org/. 8*4882a593Smuzhiyun 9*4882a593SmuzhiyunUEFI is an evolution of its predecessor 'EFI', so the terms EFI and 10*4882a593SmuzhiyunUEFI are used somewhat interchangeably in this document and associated 11*4882a593Smuzhiyunsource code. As a rule, anything new uses 'UEFI', whereas 'EFI' refers 12*4882a593Smuzhiyunto legacy code or specifications. 13*4882a593Smuzhiyun 14*4882a593SmuzhiyunUEFI support in Linux 15*4882a593Smuzhiyun===================== 16*4882a593SmuzhiyunBooting on a platform with firmware compliant with the UEFI specification 17*4882a593Smuzhiyunmakes it possible for the kernel to support additional features: 18*4882a593Smuzhiyun 19*4882a593Smuzhiyun- UEFI Runtime Services 20*4882a593Smuzhiyun- Retrieving various configuration information through the standardised 21*4882a593Smuzhiyun interface of UEFI configuration tables. (ACPI, SMBIOS, ...) 22*4882a593Smuzhiyun 23*4882a593SmuzhiyunFor actually enabling [U]EFI support, enable: 24*4882a593Smuzhiyun 25*4882a593Smuzhiyun- CONFIG_EFI=y 26*4882a593Smuzhiyun- CONFIG_EFIVAR_FS=y or m 27*4882a593Smuzhiyun 28*4882a593SmuzhiyunThe implementation depends on receiving information about the UEFI environment 29*4882a593Smuzhiyunin a Flattened Device Tree (FDT) - so is only available with CONFIG_OF. 30*4882a593Smuzhiyun 31*4882a593SmuzhiyunUEFI stub 32*4882a593Smuzhiyun========= 33*4882a593SmuzhiyunThe "stub" is a feature that extends the Image/zImage into a valid UEFI 34*4882a593SmuzhiyunPE/COFF executable, including a loader application that makes it possible to 35*4882a593Smuzhiyunload the kernel directly from the UEFI shell, boot menu, or one of the 36*4882a593Smuzhiyunlightweight bootloaders like Gummiboot or rEFInd. 37*4882a593Smuzhiyun 38*4882a593SmuzhiyunThe kernel image built with stub support remains a valid kernel image for 39*4882a593Smuzhiyunbooting in non-UEFI environments. 40*4882a593Smuzhiyun 41*4882a593SmuzhiyunUEFI kernel support on ARM 42*4882a593Smuzhiyun========================== 43*4882a593SmuzhiyunUEFI kernel support on the ARM architectures (arm and arm64) is only available 44*4882a593Smuzhiyunwhen boot is performed through the stub. 45*4882a593Smuzhiyun 46*4882a593SmuzhiyunWhen booting in UEFI mode, the stub deletes any memory nodes from a provided DT. 47*4882a593SmuzhiyunInstead, the kernel reads the UEFI memory map. 48*4882a593Smuzhiyun 49*4882a593SmuzhiyunThe stub populates the FDT /chosen node with (and the kernel scans for) the 50*4882a593Smuzhiyunfollowing parameters: 51*4882a593Smuzhiyun 52*4882a593Smuzhiyun========================== ====== =========================================== 53*4882a593SmuzhiyunName Size Description 54*4882a593Smuzhiyun========================== ====== =========================================== 55*4882a593Smuzhiyunlinux,uefi-system-table 64-bit Physical address of the UEFI System Table. 56*4882a593Smuzhiyun 57*4882a593Smuzhiyunlinux,uefi-mmap-start 64-bit Physical address of the UEFI memory map, 58*4882a593Smuzhiyun populated by the UEFI GetMemoryMap() call. 59*4882a593Smuzhiyun 60*4882a593Smuzhiyunlinux,uefi-mmap-size 32-bit Size in bytes of the UEFI memory map 61*4882a593Smuzhiyun pointed to in previous entry. 62*4882a593Smuzhiyun 63*4882a593Smuzhiyunlinux,uefi-mmap-desc-size 32-bit Size in bytes of each entry in the UEFI 64*4882a593Smuzhiyun memory map. 65*4882a593Smuzhiyun 66*4882a593Smuzhiyunlinux,uefi-mmap-desc-ver 32-bit Version of the mmap descriptor format. 67*4882a593Smuzhiyun========================== ====== =========================================== 68