x86: Add a 64-bit 'coreboot64' build

Coreboot is a first-stage bootloader mostly used on x86 devices as an
alternative to UEFI. Coreboot runs in 32-bit mode.

U-Boot currently supports booting from coreboot as a second-stage
bootloader, also in 32-bit mode. However it is useful to be able to run
U-Boot in 64-bit mode. To do this we can have a 32-bit SPL which switches
over the CPU and jumps to a 64-bit U-Boot proper.

Add a new 'coreboot64' board for running 64-bit U-Boot from coreboot. This
uses binman to create an image with a 32-bit SPL and a 64-bit U-Boot.

This allows running 64-bit EFI images on x86, for example, without needing
a native U-Boot port for a board.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/doc/board/coreboot/coreboot.rst b/doc/board/coreboot/coreboot.rst
index fd974229eb4..9c44c025a48 100644
--- a/doc/board/coreboot/coreboot.rst
+++ b/doc/board/coreboot/coreboot.rst
@@ -40,3 +40,13 @@ To enable video you must enable these options in coreboot:
 At present it seems that for Minnowboard Max, coreboot does not pass through
 the video information correctly (it always says the resolution is 0x0). This
 works correctly for link though.
+
+64-bit U-Boot
+-------------
+
+In addition to the 32-bit 'coreboot' build there is a 'coreboot64' build. This
+produces an image which can be booted from coreboot (32-bit). Internally it
+works by using a 32-bit SPL binary to switch to 64-bit for running U-Boot. It
+can be useful for running UEFI applications, for example.
+
+This has only been lightly tested.