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authorGrant Likely <grant.likely@arm.com>2018-09-06 19:29:27 +0100
committerJonathan Corbet <corbet@lwn.net>2018-09-09 14:46:44 -0600
commit9331e5e7b848edfced6b35547888eae913e3e189 (patch)
treeb7094b1bb308f5c6c2a7ab85c3073cc6fc80a697 /Documentation/efi-stub.txt
parent2f4830ef96d21e144b742c394eb12888b0e233cc (diff)
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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 <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>
Diffstat (limited to 'Documentation/efi-stub.txt')
-rw-r--r--Documentation/efi-stub.txt17
1 files 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
+CONFIGURATION TABLE.
+
+"dtb=" is processed in the same manner as the "initrd=" option that is
described above.