uefi.rst 2.8 KB

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