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doc: efi-stub.txt updates for ARM

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Update efi-stub.txt documentation to be more general
and not x86 specific.  Add ARM only "dtb=" command
line option description.

Signed-off-by: Roy Franz <roy.franz@linaro.org>
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>
This commit is contained in:
Roy Franz 2013-09-28 08:44:21 -07:00 committed by Matt Fleming
parent adaf568784
commit 719e284369
1 changed files with 20 additions and 7 deletions
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27
Documentation/efi-stub.txt
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@ -1,13 +1,16 @@
The EFI Boot Stub
---------------------------
On the x86 platform, a bzImage can masquerade as a PE/COFF image,
thereby convincing EFI firmware loaders to load it as an EFI
executable. The code that modifies the bzImage header, along with the
EFI-specific entry point that the firmware loader jumps to are
collectively known as the "EFI boot stub", and live in
On the x86 and ARM platforms, a kernel zImage/bzImage can masquerade
as a PE/COFF image, thereby convincing EFI firmware loaders to load
it as an EFI executable. The code that modifies the bzImage header,
along with the EFI-specific entry point that the firmware loader
jumps to are collectively known as the "EFI boot stub", and live in
arch/x86/boot/header.S and arch/x86/boot/compressed/eboot.c,
respectively.
respectively. For ARM the EFI stub is implemented in
arch/arm/boot/compressed/efi-header.S and
arch/arm/boot/compressed/efi-stub.c. EFI stub code that is shared
between architectures is in drivers/firmware/efi/efi-stub-helper.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
@ -23,7 +26,9 @@ The bzImage located in arch/x86/boot/bzImage must be copied to the EFI
System Partition (ESP) and renamed with the extension ".efi". Without
the extension the EFI firmware loader will refuse to execute it. It's
not possible to execute bzImage.efi from the usual Linux file systems
because EFI firmware doesn't have support for them.
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.
**** Passing kernel parameters from the EFI shell
@ -63,3 +68,11 @@ Notice how bzImage.efi can be specified with a relative path. That's
because the image we're executing is interpreted by the EFI shell,
which understands relative paths, whereas the rest of the command line
is passed to bzImage.efi.
**** 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,
and is processed in the same manner as the "initrd=" option that is
described above.