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efi_stub: update documentation on dtb= parameter

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The dtb= parameter is no longer the primary mechanism for providing a
devicetree to the kernel. Now either firmware or the boot selector (ex.
Grub) should provide the devicetree and dtb= should only be used for
debug or when using firmware that doesn't understand DT.
Update the EFI stub documentation to reflect the current usage.

Signed-off-by: Grant Likely <grant.likely@arm.com>
Reviewed-by: Alexander Graf <agraf@suse.de>
Acked-by: Leif Lindholm <leif.lindholm@linaro.org>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Grant Likely 2018-09-06 19:29:27 +01:00 committed by Jonathan Corbet
parent 2f4830ef96
commit 9331e5e7b8
1 changed files with 14 additions and 3 deletions
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17
Documentation/efi-stub.txt
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@ -83,7 +83,18 @@ is passed to bzImage.efi.
The "dtb=" 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
For the ARM and arm64 architectures, a device tree must be provided to
the kernel. Normally firmware shall supply the device tree via the
EFI CONFIGURATION TABLE. However, the "dtb=" command line option can
be used to override the firmware supplied device tree, or to supply
one when firmware is unable to.
Please note: Firmware adds runtime configuration information to the
device tree before booting the kernel. If dtb= is used to override
the device tree, then any runtime data provided by firmware will be
lost. The dtb= option should only be used either as a debug tool, or
as a last resort when a device tree is not provided in the EFI
CONFIGURATION TABLE.
"dtb=" is processed in the same manner as the "initrd=" option that is
described above.