kernel-ark/Documentation/arm/uefi.txt
Linus Torvalds 2dc10ad81f arm64 updates for 4.4:
- "genirq: Introduce generic irq migration for cpu hotunplugged" patch
   merged from tip/irq/for-arm to allow the arm64-specific part to be
   upstreamed via the arm64 tree
 
 - CPU feature detection reworked to cope with heterogeneous systems
   where CPUs may not have exactly the same features. The features
   reported by the kernel via internal data structures or ELF_HWCAP are
   delayed until all the CPUs are up (and before user space starts)
 
 - Support for 16KB pages, with the additional bonus of a 36-bit VA
   space, though the latter only depending on EXPERT
 
 - Implement native {relaxed, acquire, release} atomics for arm64
 
 - New ASID allocation algorithm which avoids IPI on roll-over, together
   with TLB invalidation optimisations (using local vs global where
   feasible)
 
 - KASan support for arm64
 
 - EFI_STUB clean-up and isolation for the kernel proper (required by
   KASan)
 
 - copy_{to,from,in}_user optimisations (sharing the memcpy template)
 
 - perf: moving arm64 to the arm32/64 shared PMU framework
 
 - L1_CACHE_BYTES increased to 128 to accommodate Cavium hardware
 
 - Support for the contiguous PTE hint on kernel mapping (16 consecutive
   entries may be able to use a single TLB entry)
 
 - Generic CONFIG_HZ now used on arm64
 
 - defconfig updates
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Merge tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux

Pull arm64 updates from Catalin Marinas:

 - "genirq: Introduce generic irq migration for cpu hotunplugged" patch
   merged from tip/irq/for-arm to allow the arm64-specific part to be
   upstreamed via the arm64 tree

 - CPU feature detection reworked to cope with heterogeneous systems
   where CPUs may not have exactly the same features.  The features
   reported by the kernel via internal data structures or ELF_HWCAP are
   delayed until all the CPUs are up (and before user space starts)

 - Support for 16KB pages, with the additional bonus of a 36-bit VA
   space, though the latter only depending on EXPERT

 - Implement native {relaxed, acquire, release} atomics for arm64

 - New ASID allocation algorithm which avoids IPI on roll-over, together
   with TLB invalidation optimisations (using local vs global where
   feasible)

 - KASan support for arm64

 - EFI_STUB clean-up and isolation for the kernel proper (required by
   KASan)

 - copy_{to,from,in}_user optimisations (sharing the memcpy template)

 - perf: moving arm64 to the arm32/64 shared PMU framework

 - L1_CACHE_BYTES increased to 128 to accommodate Cavium hardware

 - Support for the contiguous PTE hint on kernel mapping (16 consecutive
   entries may be able to use a single TLB entry)

 - Generic CONFIG_HZ now used on arm64

 - defconfig updates

* tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux: (91 commits)
  arm64/efi: fix libstub build under CONFIG_MODVERSIONS
  ARM64: Enable multi-core scheduler support by default
  arm64/efi: move arm64 specific stub C code to libstub
  arm64: page-align sections for DEBUG_RODATA
  arm64: Fix build with CONFIG_ZONE_DMA=n
  arm64: Fix compat register mappings
  arm64: Increase the max granular size
  arm64: remove bogus TASK_SIZE_64 check
  arm64: make Timer Interrupt Frequency selectable
  arm64/mm: use PAGE_ALIGNED instead of IS_ALIGNED
  arm64: cachetype: fix definitions of ICACHEF_* flags
  arm64: cpufeature: declare enable_cpu_capabilities as static
  genirq: Make the cpuhotplug migration code less noisy
  arm64: Constify hwcap name string arrays
  arm64/kvm: Make use of the system wide safe values
  arm64/debug: Make use of the system wide safe value
  arm64: Move FP/ASIMD hwcap handling to common code
  arm64/HWCAP: Use system wide safe values
  arm64/capabilities: Make use of system wide safe value
  arm64: Delay cpu feature capability checks
  ...
2015-11-04 14:47:13 -08:00

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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_EFI_VARS=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.
--------------------------------------------------------------------------------