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Diffstat (limited to 'doc')
| -rw-r--r-- | doc/arch/x86.rst | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/doc/arch/x86.rst b/doc/arch/x86.rst index a441738ad13..c6b70ce61a3 100644 --- a/doc/arch/x86.rst +++ b/doc/arch/x86.rst @@ -712,6 +712,34 @@ to load a 'u-boot-payload.efi', see below test logs on QEMU. See :doc:`../uefi/u-boot_on_efi` and :doc:`../uefi/uefi` for details of EFI support in U-Boot. +Chain-loading +------------- +U-Boot can be chain-loaded from another bootloader, such as coreboot or +Slim Bootloader. Typically this is done by building for targets 'coreboot' or +'slimbootloader'. + +For example, at present we have a 'coreboot' target but this runs very +different code from the bare-metal targets, such as coral. There is very little +in common between them. + +It is useful to be able to boot the same U-Boot on a device, with or without a +first-stage bootloader. For example, with chromebook_coral, it is helpful for +testing to be able to boot the same U-Boot (complete with FSP) on bare metal +and from coreboot. It allows checking of things like CPU speed, comparing +registers, ACPI tables and the like. + +To do this you can use ll_boot_init() in appropriate places to skip init that +has already been done by the previous stage. This works by setting a +GD_FLG_NO_LL_INIT flag when U-Boot detects that it is running from another +bootloader. + +With this feature, you can build a bare-metal target and boot it from +coreboot, for example. + +Note that this is a development feature only. It is not intended for use in +production environments. Also it is not currently part of the automated tests +so may break in the future. + TODO List --------- - Audio |