Describe how a device tree and an initial RAM disk can be passed to the EFI Boot Stub. Signed-off-by: Heinrich Schuchardt <xypron.glpk@xxxxxx> --- Documentation/admin-guide/efi-stub.rst | 35 ++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) diff --git a/Documentation/admin-guide/efi-stub.rst b/Documentation/admin-guide/efi-stub.rst index 833edb0d0bc4..86f50a33884c 100644 --- a/Documentation/admin-guide/efi-stub.rst +++ b/Documentation/admin-guide/efi-stub.rst @@ -38,6 +38,34 @@ arch/arm/boot/zImage should be copied to the system partition, and it may not need to be renamed. Similarly for arm64, arch/arm64/boot/Image should be copied but not necessarily renamed. +Passing an initial RAM disk to the EFI Boot Stub +------------------------------------------------ + +The following means sorted by decreasing priority can be used to provide an +initial RAM disk to the EFI Boot Stub: + +* The firmware may provide a UEFI Load File 2 Protocol. The stub will try to + load the RAM disk by calling the LoadFile() service of the protocol using + a vendor device path with the vendor GUID + 5568e427-0x68fc-4f3d-ac74-ca555231cc68. +* Next the EFI stub will try to load the file indicated by the "initrd=" command + line parameter. +* The prior boot stage may pass the location of the initial RAM disk via the + "linux,initrd-start" and "linux,initrd-end" properties of the "/chosen" node + of the device-tree. + +The first two items are inhibited by the "noinitrd" command line parameter. + +Passing a device-tree to the EFI Boot Stub +------------------------------------------ + +A device-tree can be passed to the EFI Boot Stub in decreasing priority using + +* command line option dtb= +* a UEFI configuration table with GUID b1b621d5-f19c-41a5-830b-d9152c69aae0. + +The command line option is only available if CONFIG_EFI_ARMSTUB_DTB_LOADER=y +and secure boot is disabled. Passing kernel parameters from the EFI shell -------------------------------------------- @@ -46,6 +74,10 @@ Arguments to the kernel can be passed after bzImage.efi, e.g.:: fs0:> bzImage.efi console=ttyS0 root=/dev/sda4 +The "noinitrd" option +--------------------- + +The "noinitrd" option stops the EFI stub from loading an initial RAM disk. The "initrd=" option -------------------- @@ -98,3 +130,6 @@ CONFIGURATION TABLE. "dtb=" is processed in the same manner as the "initrd=" option that is described above. + +This option is only available if CONFIG_EFI_ARMSTUB_DTB_LOADER=y and secure +boot is disabled. -- 2.28.0
