ARM: simplify handover from UEFI to decompressor

Hello Russell,

As discussed in the context of Geert's reverted v6 of the DTB memory node discovery patch [0], EFI boot is one possible workaround for systems where the base of memory is not a round multiple of 128 MB. U-boot today supports the bootefi command out of the box, so this does not require any special firmware.

So please pull the changes below for v5.8

[0] https://lore.kernel.org/linux-arm-kernel/[email protected]/

The following changes since commit a780e485b5768e78aef087502499714901b68cc4:

ARM: 8971/1: replace the sole use of a symbol with its definition (2020-04-29 13:30:20 +0100)

are available in the Git repository at:

git://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git tags/efi-arm-no-relocate-for-rmk

for you to fetch changes up to d0f9ca9be11f25ef4151195eab7ea36d136084f6:

ARM: decompressor: run decompressor in place if loaded via UEFI (2020-05-19 18:23:22 +0200)

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Simplify EFI handover to decompressor

The EFI stub in the ARM kernel runs in the context of the firmware, which means it usually runs with the caches and MMU on. Currently, we relocate the zImage so it appears in the first 128 MiB, disable the MMU and caches and invoke the decompressor via its ordinary entry point. However, since we can pass the base of DRAM directly, there is no need to relocate the zImage, which also means there is no need to disable and re-enable the caches and create new page tables etc.

This also allows systems whose DRAM start address is not a round multiple of 128 MB to decompress the kernel proper to the base of memory, ensuring that all memory is usable at runtime.

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Ard Biesheuvel (5):
ARM: decompressor: move headroom variable out of LC0
ARM: decompressor: split off _edata and stack base into separate object
ARM: decompressor: defer loading of the contents of the LC0 structure
ARM: decompressor: move GOT into .data for EFI enabled builds
ARM: decompressor: run decompressor in place if loaded via UEFI

 arch/arm/boot/compressed/head.S           | 79 +++++++++++++------------------
 arch/arm/boot/compressed/vmlinux.lds.S    |  5 ++
 drivers/firmware/efi/libstub/arm32-stub.c | 45 +++---------------
 3 files changed, 43 insertions(+), 86 deletions(-)