doc: arm64: add description of EFI stub support
Add explanation of arm64 EFI stub and kernel image header changes
needed to masquerade as a PE/COFF application.
Signed-off-by: Mark Salter <msalter@redhat.com>
Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
Acked-by: Grant Likely <grant.likely@linaro.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
diff --git a/Documentation/efi-stub.txt b/Documentation/efi-stub.txt
index 26be7b0..7747024 100644
--- a/Documentation/efi-stub.txt
+++ b/Documentation/efi-stub.txt
@@ -12,6 +12,11 @@
arch/arm/boot/compressed/efi-stub.c. EFI stub code that is shared
between architectures is in drivers/firmware/efi/efi-stub-helper.c.
+For arm64, there is no compressed kernel support, so the Image itself
+masquerades as a PE/COFF image and the EFI stub is linked into the
+kernel. The arm64 EFI stub lives in arch/arm64/kernel/efi-entry.S
+and arch/arm64/kernel/efi-stub.c.
+
By using the EFI boot stub it's possible to boot a Linux kernel
without the use of a conventional EFI boot loader, such as grub or
elilo. Since the EFI boot stub performs the jobs of a boot loader, in
@@ -28,7 +33,8 @@
not possible to execute bzImage.efi from the usual Linux file systems
because EFI firmware doesn't have support for them. For ARM the
arch/arm/boot/zImage should be copied to the system partition, and it
-may not need to be renamed.
+may not need to be renamed. Similarly for arm64, arch/arm64/boot/Image
+should be copied but not necessarily renamed.
**** Passing kernel parameters from the EFI shell
@@ -72,7 +78,7 @@
**** The "dtb=" option
-For the ARM architecture, we also need to be able to provide a device
-tree to the kernel. This is done with the "dtb=" command line option,
+For the ARM and arm64 architectures, we also need to be able to provide a
+device tree to the kernel. This is done with the "dtb=" command line option,
and is processed in the same manner as the "initrd=" option that is
described above.