From 9331e5e7b848edfced6b35547888eae913e3e189 Mon Sep 17 00:00:00 2001 From: Grant Likely <grant.likely@arm.com> Date: Thu, 6 Sep 2018 19:29:27 +0100 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 <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> --- 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 41df801f9a507..833edb0d0bc4a 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. -- GitLab