On 6 September 2018 at 20:29, Grant Likely <grant.likely@xxxxxxx> wrote: > 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@xxxxxxx> > Reviewed-by: Alexander Graf <agraf@xxxxxxx> > Acked-by: Leif Lindholm <leif.lindholm@xxxxxxxxxx> > Acked-by: Olof Johansson <olof@xxxxxxxxx> > Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > Cc: Jonathan Corbet <corbet@xxxxxxx> Acked-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > --- > > Resending because original post included Arm corporate disclaimer. > > 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 > +CONFIGURATION TABLE. > + > +"dtb=" is processed in the same manner as the "initrd=" option that is > described above. > -- > 2.11.0 >
