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Subject[PATCH] efi_stub: update documentation on dtb= parameter
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 <>
Cc: Ard Biesheuvel <>
Cc: Jonathan Corbet <>
Documentation/efi-stub.txt | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/Documentation/efi-stub.txt b/Documentation/efi-stub.txt
index 41df801f9a50..833edb0d0bc4 100644
--- a/Documentation/efi-stub.txt
+++ b/Documentation/efi-stub.txt
@@ -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
+"dtb=" is processed in the same manner as the "initrd=" option that is
described above.
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