Update Linux to v5.4.2
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+================================================
+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_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.
+========================== ====== ===========================================